HomeMy WebLinkAbout08 Final Draft Drainage Memo with AttachmentsA16.0187.00 7 April 2017
FINAL DRAFT SUBMITTAL
Strander Grade Separation Phase 3
Stormwater System Conceptual
Design Report
Submitted to
City of Tukwila
Tukwila, Washington
Final Draft Submittal
Stormwater System Conceptual Design Report
Strander Grade Separation Phase 3
Submitted to
City of Tukwila
Tukwila, Washington
7 April 2017
Submitted by
BergerABAM
33301 Ninth Avenue South, Suite 300
Federal Way, Washington 98003
A16.0187.00, Task 015
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page ii of xiii
FINAL DRAFT SUBMITTAL
Stormwater System Conceptual Design Report
Strander Grade Separation Phase 3
TABLE OF CONTENTS
SECTION PAGE Executive Summary ......................................................................................................................... vi
Introduction ......................................................................................................................... vi
Existing Conditions and Key Design Constraints ................................................................ vi
Anticipated Flow Rates and Pumping Capacities .............................................................. vii
Storm System Design Concepts ........................................................................................ viii
Conclusions and Recommendations ................................................................................... xi
1.0 Introduction and Purpose .................................................................................................... 1
1.1 Introduction ............................................................................................................. 1
1.2 Project Background................................................................................................. 1
1.3 Purpose of Study...................................................................................................... 2
2.0 Existing Conditions.............................................................................................................. 4
2.1 Existing Phase 1 and Phase 2 Roadway Sections................................................... 4
2.2 Existing Phase 2 Stormwater System ..................................................................... 5
2.3 Summary of Soil Conditions .................................................................................... 5
2.4 BNSF Bridge Foundation ......................................................................................... 6
2.5 Groundwater Chemical Composition ....................................................................... 7
2.6 Wetlands ............................................................................................................... 11
3.0 Phase 3 Groundwater Volumes ......................................................................................... 14
3.1 Introduction ........................................................................................................... 14
3.2 Overview of Conceptual Site Model....................................................................... 14
3.3 Flow Model Development and Calibration ............................................................ 17
3.4 Predictive Simulations........................................................................................... 19
3.5 Flow Mitigation Options ........................................................................................ 20
3.6 Preliminary Recommended Design Flows for an Unsealed (non-watertight)
Underpass.............................................................................................................. 24
4.0 Implications of New Stormwater Standards ...................................................................... 26
4.1 Wetland Hydroperiod Criteria ................................................................................ 26
4.2 Mandatory Flow Control Best Management Practices ......................................... 27
4.3 LID Performance Standard .................................................................................... 28
5.0 Overview of Stormwater System Components .................................................................. 29
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page iii of xiii
5.1 Pump Station System(s) Options ........................................................................... 29
5.1.1 Introduction ............................................................................................... 29
5.1.2 Existing Pump Station ............................................................................... 30
5.1.3 Separated Groundwater and Stormwater Flows........................................ 31
5.1.4 Combined Groundwater and Stormwater Flows ........................................ 33
5.1.5 Evaluation of Pump Station Options .......................................................... 34
5.2 Water Quality ......................................................................................................... 34
5.2.1 Treatment Requirements........................................................................... 34
5.2.2 Sizing and Flow Rate Considerations ........................................................ 35
5.2.3 Wet Biofiltration Swale ............................................................................. 35
5.2.4 Constructed Stormwater Wetland ............................................................. 36
5.2.5 Bioretention Pond with Underdrain ........................................................... 37
5.2.6 Evaluation of Water Quality Treatment Options ........................................ 38
5.3 Detention Facility .................................................................................................. 39
5.3.1 Detention Pond with Walls ........................................................................ 39
5.3.2 Detention Pond with 3H:1V Side Slopes.................................................... 40
5.3.3 Constructed Combined Wetland Pond ...................................................... 40
5.3.4 Evaluation of Treatment Options ............................................................... 41
5.4 Outfall Location ..................................................................................................... 41
5.4.1 Northern Outfall near Green River Bridge ................................................. 42
5.4.2 Southern Outfall Southwest of Substation ................................................ 43
5.4.3 Evaluation of Outfall Locations ................................................................. 43
5.5 Discharge Route .................................................................................................... 44
5.5.1 Force Main Discharge Route within Strander Boulevard Right-of-Way..... 44
5.5.2 Gravity-Fed Discharge Route within Easements ....................................... 46
5.5.3 Evaluation of Discharge Routes ................................................................ 48
6.0 Storm System Build Alternatives ....................................................................................... 49
6.1 Storm System Build Alternative No. 1 ................................................................... 49
6.2 Storm System Build Alternative No. 2 ................................................................... 51
6.3 Storm System Build Alternative No. 3 ................................................................... 53
6.4 Storm System Build Alternative No. 4 ................................................................... 55
6.5 Storm System Build Alternative No. 5 ................................................................... 57
6.6 Storm System Build Alternative No. 6 ................................................................... 59
6.7 Pump Station Cost Summary................................................................................. 62
7.0 Conclusions and Recommendations ................................................................................. 63
7.1 Need for a Watertight Underpass .......................................................................... 63
7.2 Preferred Treatment and Detention Alternative .................................................... 64
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page iv of xiii
7.3 Opinion of Probable Project Cost .......................................................................... 67
7.4 Recommendations for Future Work ...................................................................... 67
7.4.1 Outreach to Property Owners regarding Required Easements.................. 67
7.4.2 Confirm Use of Temporary Tiebacks for Walls........................................... 67
7.4.3 Confirm South Outfall Location ................................................................. 67
7.4.4 Model Wetland Q/R Inundation ................................................................ 67
7.4.5 Update Groundwater Model ...................................................................... 67
7.4.6 Obtain Flow Metering Data Upstream of Existing Pump Station .............. 68
8.0 List of Acronyms and Abbreviations .................................................................................. 69
LIST OF TABLES
Table 1. Water Budget for Stormwater Pond – Phase 3 Base Case.............................................. 19
Table 2. Estimated Water Budget for Phase 3 Mitigation Cases .................................................. 21
Table 3. Pump Station Cost Summary ........................................................................................... 62
Table 4. Project Flow Rates........................................................................................................... 63
LIST OF FIGURES
Figure 1. Project Phasing ................................................................................................................ 3
Figure 2. Typical Section of Phase 2 Roadway Underpass.............................................................. 4
Figure 3. Overexcavation for BNSF Bridge Foundation ................................................................... 7
Figure 4. Construction Dewatering Pipes........................................................................................ 8
Figure 5. Underdrain System Cleanout............................................................................................ 9
Figure 6. Underdrain Water Sample ................................................................................................ 9
Figure 7. Underdrain Water Sample Settling ................................................................................ 10
Figure 8. Storm System Water Sample ......................................................................................... 10
Figure 9. Wetlands Q/R, A, B, and portions of C (Wetlands D and E to south not shown) ............ 12
Figure 10. Springbrook Creek Wetland and Habitat Mitigation Bank .......................................... 13
Figure 11. Conceptual Water Budget for Phase 2 System ............................................................ 16
Figure 12. Transient Calibration Results – Phase 2 Underdrain Groundwater Inflow .................. 18
Figure 13. Model-Predicted Groundwater Inflow to Phase 3 Underdrain System ......................... 22
Figure 14. Model-Predicted Overflow from Phase 3 Stormwater Pond ......................................... 23
Figure 15. Schematic of Existing Pump Station System ............................................................... 31
Figure 16. Groundwater and Upgraded Stormwater Pump Stations ............................................. 32
Figure 17. Energy Dissipator ......................................................................................................... 33
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page v of xiii
Figure 18. Single Structure Configuration to Provide Energy Dissipation and Serve as
Flow Splitter ................................................................................................................ 34
Figure 19. Biofiltration Swale Section .......................................................................................... 36
Figure 20. Constructed Stormwater Wetland Section .................................................................. 37
Figure 21. Bioretention Pond Section ........................................................................................... 38
Figure 22. Detention Pond with Walls Section.............................................................................. 40
Figure 23. Detention Pond Section ............................................................................................... 40
Figure 24. Combined Water Quality and Detention Pond Section ................................................ 40
Figure 25. Tideflex Valve ............................................................................................................... 42
Figure 26. Northern Outfall............................................................................................................ 43
Figure 27. Southern Outfall ........................................................................................................... 43
Figure 28. Discharge Routes within Strander Boulevard Right-of-Way......................................... 45
Figure 29. Secondary Discharge Pump Station (Shown with groundwater and stormwater
combined. Separated flows would be similar.) ............................................................ 46
Figure 30. Discharge Routes within Easements ........................................................................... 47
Figure 31. Schematic Configuration of Alternative No. 1 ............................................................. 50
Figure 32. Schematic Configuration of Alternative No. 2 ............................................................. 52
Figure 33. Schematic Configuration of Alternative No. 3 ............................................................. 54
Figure 34. Schematic Configuration of Alternative No. 4 ............................................................. 56
Figure 35. Off-Site Constructed Wetland Section ......................................................................... 57
Figure 36. Schematic Configuration of Alternative No. 5 ............................................................. 58
Figure 37. Off-Site Bioretention Section ....................................................................................... 60
Figure 38. Schematic Configuration of Alternative No. 6 ............................................................. 61
Figure 39. Alternative No. 4 - Preferred Treatment and Detention Alternative ............................. 66
LIST OF APPENDICES
Appendix A. Draft Hydrogeologic Study by Shannon & Wilson, Inc.
Appendix B. Wetland Technical Memorandum by David Evans and Associates
Appendix C. Phase 3 Potential Impacts Exhibit
Appendix D. Existing Outfall Conditions Memorandum by Widener & Associates
Appendix E. Project Footprint Areas
Appendix F. Opinion of Probable Project Costs
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page vi of xiii
EXECUTIVE SUMMARY
Introduction
A key issue for the design of the full buildout of Strander Boulevard is to determine if the
project would need to be watertight as originally envisioned. The cost of making the underpass
watertight is estimated to be $10 million. This report describes the results of geotechnical
investigations, groundwater modeling, and design development of stormwater system concepts
required to determine if the project should be watertight and to provide the basis for the final
design of the project.
Existing Conditions and Key Design Constraints
In order to reduce the cost of the initial construction phases of the project, an underpass of the
BNSF railroad was completed by installing a pump station to pump both stormwater and
groundwater entering the roadway excavation from the surrounding area. The volume of
groundwater was anticipated to be small enough that it could be combined with the
stormwater, which was to be treated in wetpond and discharged to adjoining wetland. This was
envisioned as an interim condition until construction of a full, four-lane arterial connection of
Strander Boulevard to Southwest 27th Street. The full buildout was anticipated to require the
construction of watertight walls and a bottom seal for the underpasses, effectively eliminating
the groundwater inflows.
A summary of experience acquired during construction of the BNSF underpass and a summary
of existing conditions that will constrain the design of the next phase of the project is provided
in Section 2.0 of this report. One of the key constraints are the numerous wetlands in the project
vicinity. David Evans and Associates prepared a Wetland Technical Memorandum for the City
of Renton in November 2007. The main body of the above-mentioned memo is located in
Appendix B.
Providing the correct discharge to adjacent wetlands proved difficult with the currently
constructed interim project. Because the King County Surface Water Design Manual
(KCSWDM) has recently been updated to conform to the 2014 Washington State Department of
Ecology (Ecology) Stormwater Management Manual of Western Washington, and KCSWDM
has been preliminarily approved by Ecology, the completed project will need to comply with
this manual. Meeting the new KCSWDM wetland hydroperiod criteria is the most significant
challenge for design of the stormwater system for the project.
Because hydrology is one of most important determinant of the establishment and maintenance
of specific types of wetlands and wetland processes, changes to a wetland’s hydroperiod
resulting from the construction of the project need to be controlled and minimized. The new
standard accomplishes this in a different manner than the previous standard as described in
Section 4.0 of this report. Because of these changes, the project cannot discharge all of the
stormwater flows to the adjacent wetlands and will require that an alternative outfall location
be used. Potential outfall locations are discussed in Section 5.0 of this report.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page vii of xiii
One of the other important characteristics of the site is the presence of dissolved iron in the
groundwater. Dissolved iron is abundant in the groundwater at the site. Siderophilic bacteria
are microorganisms in the soil that obtain energy by oxidizing dissolved iron, which is a
chemical reaction similar to forming rust. The by-product of the oxidation process is insoluble
iron that precipitates out of water as a rust colored, gelatinous insoluble iron or an oily sheen.
The orange water does not pose a health concern and is a source of nutrients for plants but is
aesthetically unappealing to the general public who may not understand the source of the
coloration. Discharging this water into the nearby Green River could create visibly detectable
plumes, depending on the volume of the discharge. It is difficult to predict what a detectable
volume of discharge would be and whether this would lead to community concerns. The
discharge would be constant throughout the rainy season and correcting it after construction is
completed may be difficult. The insoluble iron can also coat the walls of pipes and pump
systems, causing long-term maintenance concerns. During construction, the inside pipes of the
dewatering pump system became partially clogged with this material as described in
Section 2.0.
Anticipated Flow Rates and Pumping Capacities
Shannon & Wilson performed subsurface explorations and installed groundwater observation
instruments to evaluate the subsurface conditions and provide permanent dewatering and
stormwater pumping requirements for the planned extension of the Strander Boulevard project
in the city of Tukwila, Washington. To support the stormwater system design, Shannon &
Wilson also developed a 3-D groundwater flow model to estimate groundwater inflows to the
planned underdrain system. The model was calibrated to existing inflows determined from the
pumping data available from the existing pump station. The development of this model is
described in Section 3.0 of this report. Overall, the model adequately reproduced the observed
pumping and discharge data obtained from the existing facility. Appendix A contains
additional detailed information about the model development and calibration.
The model predicts that the groundwater inflow to the underdrains of an unsealed underpass
would be between 150 gallons per minute (gpm) (average annual conditions) and 355 gpm (wet
winter conditions). Assuming that the total inflow to the pump station is conveyed to the
stormwater pond, the estimated overflow from the pond to the wetlands and channel is
expected to be between 130 gpm (average annual conditions) and 405 gpm (wet winter
conditions). A significant source of this inflow is the excavation for the construction of the
foundation for the BNSF railroad bridge. This excavation could be sealed with grout to reduce
the inflow of groundwater.
Note that the peak roadway runoff during storm events is much larger than these seasonal
averages. Peak runoff, combined with the limitations of storage volume in the wet well for the
pump system, results in a required pumping capacities of approximately 6,600 gpm in the
100-year storm event, as described in Section 5.0 of this report.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page viii of xiii
Although the groundwater inflows for an unsealed underpass are small, relative to the peak
storm events, they are relatively constant and there is some uncertainty predicting the design
flow for the project if it were to be constructed without a watertight bottom seal and walls.
Those uncertainties are primarily related to the following issues.
1. Variations in actual, in-situ, soil properties from those assumed in the groundwater
model.
2. Effectiveness of any grouting of the BNSF foundation excavation performed to seal the
excavation.
3. Uncertainties in predicting the combination of winter weather and peak storm events that
should be used.
For the purpose of this study, a groundwater inflow of 355 gpm was used for an unsealed
underpass. Designing for 355 gpm provides adequate system reserve capacity should more
permeable subsurface soils be encountered and/or more extreme weather events occur and/or
the grouting of the “window” through the He layer is not 100 percent effective. Alternatively, a
more rigorous, probability-related analysis would need to be performed during final design to
arrive at a design flow.
An estimate of groundwater flow for a sealed underpass has not been made, but based on
previous experience from the watertight underpass at South 180th Street, the groundwater
flows will likely be around 25 gpm.
Storm System Design Concepts
The project is bounded to the south by Wetland Q/R. There is approximately 2.5 acres available
between the southern limits of the project and the wetland to construct both the water quality
and detention facilities. This limits what treatment and detention facilities can be incorporated
into the project. There are five main components to the stormwater system. They are
1. Pump Station System(s)
2. Water Quality Facility
3. Detention Facility
4. Outfall Location
5. Discharge Route to the Green River
There are multiple options for each of the components and they can be combined in many ways.
The options for each component have been used to develop the build alternatives summarized
below and described in greater detail in Section 5.0. Section 6.0 of this report describes the
various ways the component options can be combined into build alternatives.
Pump Station(s) - The configuration of pump station system options is dependent on whether
the groundwater and stormwater flows will be pumped separately or combined. If the flows are
pumped separately, an additional new small pump system will be required for the
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page ix of xiii
groundwater. However, this additional groundwater pump station will not be large and will be
the same whether the underpass is sealed or not. Keeping the groundwater separate from the
stormwater will also simplify the design of the detention and treatment systems because the
actual volume of groundwater inflows, and its seasonal variation, cannot be known with
certainty until after the facility is constructed. These risks are discussed further in Section 7.0.
In either case, the existing pump station will need to be upgraded to convey approximately
6,600 gpm of stormwater, required to convey the 100-year storm event and have 100 percent
redundancy. The existing rated firm pumping capacity, with 100 percent redundancy, by a
secondary pump, is approximately 3,300 gpm. The existing total pumping capacity, with no
redundancy, is approximately 6,000 gpm.
Water Quality - Per Section 1.2.8.1 of the KCSWDM, if 50 percent or more of the runoff directed
to a water quality facility is from a roadway with an expected average daily traffic count of
2,000 or more vehicles, then enhanced water quality is required. Enhanced treatment is also
required if a project discharges to a wetland.
However, per the last paragraph on page 1-72 of the KCSWDM, projects that drain entirely by
pipe to major receiving waters may revert to the basic water quality treatment standard as long
as it is not an impaired waterbody. This project will discharge by pipe to the Green River.
However, the project also discharges to a wetland; therefore, enhanced treatment is required.
If groundwater is combined with stormwater, meeting flow control requirements for the
adjacent wetland will be more difficult, particularly because the exact rate of groundwater flow,
and its seasonal variation, will not be known until the facility is constructed and been in
operation for at least a year. Post-construction adjustments to orifices and flow control devices
may be required.
The three types of water quality facilities considered for use on this project were a wet
biofiltration swale, a constructed wetland, and a biofiltration pond. Each of these is described in
more detail in Section 5.0.
Detention - If a project can outfall to a major body of water, the project is exempt from
providing detention, also known as flow control exempt. The project will be discharging to the
Green River. The Green/Duwamish River is flow control exempt downstream of River Mile 6.
The project will discharge upstream of this location; therefore, it is not flow control exempt. The
detention facilities will conform to a Level 2 flow control standard. This standard matches
developed discharge durations to predeveloped durations for the range of the predeveloped
discharge rates from 50 percent of the two-year peak flow up to the full 50-year peak flow. The
detention facility will detain up to the 100-year storm event. The predeveloped condition shall
be considered forested.
All of the detention facilities considered provide the same level of detention and are all
considered a wetpond. The difference is their geometry and whether there is sufficient space to
construct them using expensive concrete retaining walls.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page x of xiii
Outfall Location - There are two existing outfalls within the project vicinity that could be
upgraded to serve the Strander Boulevard project. Either outfall will need to be upgraded,
which will require additional permitting. The Nationwide Permit 7 is required for waters of the
United States. Washington Department of Fish and Wildlife will require Hydraulic Permit
Approval. A City of Tukwila Critical Area Permit will also be required.
The northern outfall is a corrugated metal pipe, located just south of the Strander Boulevard
Bridge that crosses the Green River. The southern outfall is located on the west side of West
Valley Highway, approximately 150 feet southwest of the Puget Sound Energy substation. The
outfall is approximately 25 feet downhill from the roadway. See Appendix D for the Existing
Outfall Conditions Memorandum.
The northern outfall will require an upgraded outfall pipe with a Tideflex duckbill to prevent
fish passage up the pipe. This pipe is below the ordinary high water level; therefore, any
construction activities will need to occur within a fish window. The southern outfall appears to
be above the ordinary high water level. The southern outfall will also require a Tideflex
duckbill, but construction activities that will need to be performed on this outfall may not be
constrained by a fish window. Therefore, the southern outfall location is tentatively consider the
preferred outfall location.
Discharge Route - There are two potential discharge routes to the Green River that are
compatible with either outfall. One route follows the proposed extension of Strander Boulevard
under the Union Pacific Railroad (UPRR), remaining within the project’s right-of-way until it
rises up again in the vicinity of West Valley Highway. The other route crosses under the UPRR
south of Strander.
The route to the south could be gravity fed and would require the City acquire three easements
to construct the discharge pipe using the northern outfall or four easements to construct a
discharge pipe to the southern outfall. The route to the north, that stays within the project right-
of-way as it crosses under UPRR, will require a secondary discharge pump station for the
stormwater and groundwater. Only one easement would be required if the northern outfall is
used. Three easements are required if the southern outfall is used.
Routing the discharge within the existing Strander Boulevard right-of-way minimizes property
acquisition costs but requires a secondary pump station at a capital cost of $1.5 million. The
secondary pump station will also increase operation and maintenance costs and life-cycle costs.
Therefore, this route is undesirable.
The alternative, southern, discharge route eliminates the need of a secondary pump station and
conveys water to the west under the UPRR embankment. As discussed above, this route
requires additional easements but the costs are significantly offset by the lack of a secondary
pump station. A gravity system appears to be feasible but survey information is required to
verify that the grades will be acceptable. Assuming the grades are acceptable, this route would
be the preferred discharge route.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page xi of xiii
Conclusions and Recommendations
Need for a Watertight Underpass - The original planning of the project envisioned that Phase 3
of the project would construct a watertight bottom seal and wall system for the entire length of
the existing Phase 2 project, as well as the Phase 3 extension. The cost of sealing the underpass
is approximately $10 million. This cost is high relative to the reduction in groundwater design
flows achieved. Groundwater inflows for an unsealed underpass are expected to be between
115 gpm to 295 gpm. Sealing the underpass would reduce these flows to 25 gpm or less.
Although the anticipated groundwater flows are small relative to the volume of stormwater
discharge, they are essentially constant throughout the wet season and continue at a reduced
rate in the summer. This creates several risks for the project as outlined below.
1. If the groundwater is combined with the stormwater and routed through the detention
and treatment facilities, it will be difficult to design the detention and treatment facilities
to function, as required, to mimic natural rainfall patterns and associated discharges to the
adjacent wetlands. The constant flow of water will essentially be passed through the
facility continuously.
2. The exact amount of groundwater inflows will not be known until the facility is
constructed and in operation for a year or more. If the groundwater and stormwater are
combined, flow control features may need to be adjusted or reconstructed after the facility
is operational to provide the required flows to detention and treatment facilities, as well as
the adjacent wetland.
3. To avoid all of the issues described above, the groundwater could be routed directly to the
Green River. However, a plume of iron-tainted water may be discharged to the Green
River on a continual basis. Even with some treatment, it is not known how visible this
plume would be. The orange water does not pose a health concern but is aesthetically
unappealing to the general public who may not understand the source of the coloration. It
is difficult to predict what a detectable volume of discharge would be and whether this
would lead to community concerns and correcting the issues after construction is
completed may be difficult. Minimizing this discharge would substantially mitigate this
risk.
4. The insoluble iron can also coat the walls of pipes and pump systems, causing long-term
maintenance concerns. During construction, the inside pipes of the dewatering pump
system became partially clogged with this material. See Figure 4 in Section 2.0 of this
report.
Therefore, based on discussions with the City, it is recommended that the groundwater be
separated from the stormwater and that additional project funding be sought to seal the
underpass and reduce groundwater inflows to an absolute minimum. This will directly mitigate
long-term maintenance risks, as well as potential concerns with the quality of discharge to the
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page xii of xiii
Green River. This will also facilitate separating the groundwater from the stormwater, which
will simplify the design of the detention and treatment facilities.
If an additional $10 million in funding cannot be secured, the groundwater should be kept
separate from the stormwater and discharged directly to the Green River, potentially through a
dedicated treatment facility, such as a filter vault. Additional study will be required to
determine if a plume of discolored water would be visible under these circumstances.
Preferred Treatment and Detention Alternative - Assuming the underpass is sealed as
recommended above, the preferred treatment and detention alternative for the project is
Alternative No. 4 as described in Section 5.0 of this report. Alternative No. 4 separates the
groundwater from the stormwater. The detention facilities are stacked above the water quality
facilities, which provides the best use of space of all of the alternatives. The usage of 3H:1V side
slopes provides easier access for maintenance activities and eliminates the need and cost for
walls to contain the detention pond.
It is recommended that some modifications to this alternative be considered prior to completing
the final design of the stormwater system. These potential modifications are outlined below.
1. Consider use of the southern outfall. Currently, this alternative discharges to the northern
outfall, which is not the preferred outfall component.
2. Consider the gravity discharge route. This alternative proposed using the Strander
Boulevard right-of-way, which minimizes easement costs but requires the secondary
discharge pump station that has a higher capital cost and also increases the long-term
maintenance costs. A gravity system appears to be feasible but survey information is
required to verify that the grades will be acceptable. Assuming the grades are acceptable,
this route would be the preferred discharge route.
As a whole, this alternative provides facilities that have low to moderate maintenance costs and
will be simple to maintain. The capital costs and long-term maintenance costs of three pump
stations may be avoided by pursuing the modifications described above.
Opinion of Probable Project Cost - An updated project cost estimate was prepared and a
summary is attached in Appendix F. The estimate includes a brief narrative describing the basic
assumptions used to prepare the estimate. The total project cost is anticipated to be $54.5
million.
Recommendations for Future Work - There are several steps that should be taken to confirm
some of the assumptions used in this preliminary design effort prior to starting the plan,
specification, and cost estimate effort. Each of these are described in greater detail in Section of
7.0 of this report.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report April 2017
Strander Grade Separation Phase 3 Page 1 of 68
1.0 INTRODUCTION AND PURPOSE
1.1 Introduction
This memorandum summarizes the results of the study to develop a design concept for
a roadway stormwater system that will support the full buildout of the extension of
Strander Boulevard under the Union Pacific Railroad (UPRR) to connect to the West
Valley Highway and widening of the previously constructed portion of Strander
Boulevard, which included an underpass of the BNSF Railway.
The stormwater system alternatives considered meet the latest King County Surface
Water Design Manual (KCSWDM) and would also comply with the project’s previously
prepared National Environmental Policy Act (NEPA) documentation and associated
commitments. The KCSWDM has recently been updated to conform to the 2014
Washington State Department of Ecology (Ecology) Stormwater Management Manual of
Western Washington (SMMWW). The KCSWDM has been preliminarily approved by
Ecology and contains new requirements that the completed project, including
previously constructed phases, will need to meet.
1.2 Project Background
The cities of Renton and Tukwila have been working in partnership to complete a
connection of Strander Boulevard in the city of Tukwila with Southwest 27th Street in
the city of Renton. The project is being completed in three phases as shown in Figure 1.
As lead agency for the first two phases of the project, the City of Renton completed an
undercrossing of the BNSF Railway in 2014, connecting Southwest 27th Street with the
Tukwila Sound Transit Station. Phase 3, to be completed by the City of Tukwila, would
construct an undercrossing of the UPRR and a four-lane arterial connection of Southwest
27th Street to Strander Boulevard and to the West Valley Highway.
In order to reduce the cost of the first two phases of the project, the BNSF undercrossing
was completed by installing a pump station to pump both stormwater and groundwater
entering the roadway excavation from the surrounding area. The volume of
groundwater was anticipated to be small enough that it could be combined with the
stormwater, which was to be treated in wetpond and discharged to adjoining wetland.
This was envisioned as an interim condition until construction of a full, four-lane arterial
connection of Strander Boulevard to Southwest 27th Street. The full buildout was
anticipated to require the construction of watertight walls and a bottom seal for the
underpasses, effectively eliminating the groundwater inflows.
Based on experience with site soil conditions obtained from construction of the BNSF
underpass, it was determined that the construction of watertight walls and a bottom seal
for the underpasses may not be required and that a stormwater pump system may be
used to permanently manage groundwater infiltrating into underpass, avoiding the cost
of making the underpass watertight. A summary of experience acquired with Phase 2 of
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Strander Grade Separation Phase 3 Page 2 of 68
the project, and existing conditions that will constrain the design of Phase 3, is provided
in Section 2.0 of this memorandum.
1.3 Purpose of Study
This memorandum includes the results of geotechnical investigations and additional
groundwater modeling performed to support the development of the Phase 3
stormwater system and provide the basis for the final design of the project. Key issues
for the design of development of Phase 3 are to confirm the amount of groundwater that
will be encountered by completing Phase 3 and determine if the full buildout of the
project would need to be watertight.
Because the design of Phase 3 is still at the concept level, this memorandum is not
intended to be a final drainage report. This memorandum is being prepared as a
decision-making tool to establish the basic design concept that will be implemented in
the completion of the design of the project. A final drainage report would be completed
as part of the project design and would be based on the final geometrics of the project.
Those geometrics may vary slightly from the concept design but are not likely to alter
the results and conclusions of this study.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report April 2017
Strander Grade Separation Phase 3 Page 3 of 68
Figure 1. Project Phasing
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Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 4 of 68
2.0 EXISTING CONDITIONS
2.1 Existing Phase 1 and Phase 2 Roadway Sections
The first phase provided at-grade improvements between Oakesdale Avenue SW and
Naches Avenue. This section of roadway is two lanes in each direction with a median
dividing the lanes. Left-turn-lane pockets are provided in the median at cross street
locations. The roadway has 5-foot planter strips behind the curb, with a 6-foot-wide
sidewalk on the north and a 12-foot-wide sidewalk on the south side. The second phase
provided the BNSF bridge and a two-lane roadway section between Naches Avenue and
the Sound Transit Driveway. A 6-foot pedestrian path was provided on the north side.
The Phase 2 roadway is approximately 25 feet lower than the existing grade as it passes
under the BNSF. To reduce costs, 3H:1V cut slopes were used where they could be
accommodated within existing right-of-way. Quarry spalls were placed on the slopes
and on the area behind the curb for protection. The roadway consists of two 11-foot
lanes, 2-foot shy distance from edge of travelled way to face of curb, curb and gutter,
and a 5-foot strip behind the curb. A 6-foot-wide pedestrian path is located at the top of
the roadway embankment, on the north side of the roadway. These conditions are
illustrated in Figure 2.
Figure 2. Typical Section of Phase 2 Roadway Underpass
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Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 5 of 68
2.2 Existing Phase 2 Stormwater System
The existing stormwater system consists of a closed conveyance system and an
underdrain system. The closed system collects roadway stormwater runoff at the gutter
in a series of catch basins. The stormwater is conveyed to the west to the low point in the
system.
The site has a high groundwater table with seasonal fluctuations between Elevations 16 feet
and 19 feet. The majority of the roadway is below the groundwater table, and an underdrain
system collects seepage from the surrounding soils and runoff from the 3H:1V side slopes.
The underdrain system consists of 8-inch-diameter perforated polyvinyl chloride (PVC)
pipes running parallel to the roadway and connected at a series of cleanouts. The underdrain
pipes are embedded in 18 inches of washed permeable ballast.
The underdrain system connects to the closed storm system downstream of the low
point. Stormwater and groundwater are comingled at this location. From this point, the
combined flows are conveyed via a 36-inch ductile iron pipe to a 6-foot-diameter inlet
manhole followed by a 10-foot-diameter wet well. The wet well houses two
50-horsepower (hp) pumps. The pumps were originally sized to handle estimated
stormwater for Phase 2.
The comingled stormwater and groundwater are pumped to a higher elevation through
a valve vault, through a meter vault, and to a 54-inch discharge manhole prior to
entering a two-celled wetpond. A more detailed description and schematic diagram of
the existing pump system is provide in Section 5.1.2. The wetpond was sized to provide
detention and basic water quality treatment of the stormwater runoff. The pond
discharges into Wetland Q/R located south of the pond. Wetland Q/R is discussed
further in Section 2.6, Wetlands, below.
The Phase 2 pump station reports pumping volumes on a continuous basis to the City of
Renton. The data collected through 1 November 2016 was obtained from the City of
Renton and used to calibrate an update to the project’s groundwater model as described
in the geotechnical report attached as Appendix A.
The stormwater system experiences high flows between 120 gallons per minute (gpm) to
250 gpm in the rainy season from the underdrain system. These flows are greater than
the estimated flows used for design of treatment facility. Due to the higher flows, the
pond does not function as it was originally intended. This situation must be addressed
in Phase 3 in order to conform to the project’s environmental commitments.
2.3 Summary of Soil Conditions
Shannon & Wilson, Inc. performed geotechnical explorations and groundwater
modeling in support of Phase 2 of the project. Additional explorations were completed
in support of the proposed Phase 3, and the groundwater model was significantly
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Strander Grade Separation Phase 3 Page 6 of 68
updated and improved. Boring logs, soil profiles, and results of the new groundwater
models are provided in Appendix A.
For the purpose of understanding groundwater infiltration, the project site can be
considered to consist of three major soil layers.
1. Railroad embankment fill along both UPRR and BNSF
2. Estuarine/overbank deposits
3. Alluvial deposits
Railroad embankment fill consists of native materials overlain with ballast and
subballast.
The estuarine/overbank deposits consist of very soft to medium stiff clayey silt and silty
clay with low permeability. The permeability is sufficiently low that groundwater
infiltration through the bottom of any roadway excavation is generally much less than
infiltration through the sides of the upper layers of soils and/or surface runoff. These
deposits extend from the ground surface (+25) to about Elevation -3 feet.
The alluvial deposits consist of medium dense to very dense silty sand. These deposits
extend from approximately Elevation -3 feet to -50 feet and have higher permeability
than the estuarine/overbank deposits. Therefore, excavation below the interface between
these two layers significantly increases the infiltration rates.
2.4 BNSF Bridge Foundation
The BNSF bridge carries three sets of rail lines over Strander Boulevard. A 9-foot-thick
concrete foundation supported on 24-inch pipe piles provides support for the BNSF
bridge, its pier, and abutment walls. The matt foundation was designed to function as
part of a bottom seal system in the full buildout, and its thickness provides the weight
required to counteract the buoyant forces of the high water table.
The elevation of the top of the roadway under the BNSF bridge is approximately +11 feet,
which is well above the interface between the less pervious estuarine/overbank deposits
and the more pervious alluvial deposits. The top and bottom of the BNSF foundation is at
approximately Elevations +9 feet and +0 foot, respectively. The bottom of the BNSF
foundation is, therefore, essentially at the interface of the these two soil layers.
During the construction of the BNSF foundation, the contractor overexcavated on both
sides of the foundation to provide quarry spall pads for construction access. The area of
the excavation is estimated to be 20 feet west and 55 feet east on each side of the
106-foot-wide foundation. Based on construction site photos, as pictured below in
Figure 3, the excavation extended into the sandy alluvial deposits (Elevation -3 feet) and
is assumed to be backfilled with permeable gravel borrow. It is suspected that
groundwater infiltration rates at this location are greater than anticipated for the design
of the treatment facilities as discussed in Section 2.2. The updated groundwater model
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Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 7 of 68
(see Appendix A) incorporates this feature and confirms that this is the most likely
source of the additional inflows being experienced with the existing facility.
Figure 3. Overexcavation for BNSF Bridge Foundation
2.5 Groundwater Chemical Composition
Dissolved iron is abundant in the groundwater. Siderophilic bacteria are
microorganisms in the soil that obtain energy by oxidizing dissolved iron, which is a
chemical reaction similar to forming rust. The by-product of the oxidation process is
insoluble iron that precipitates out of water as a rust colored, gelatinous insoluble iron
or an oily sheen.
The orange water does not pose a health concern and is a source of nutrients for plants
but is aesthetically unappealing to the general public who may not understand the
source of the coloration. Discharging this water into the nearby Green River could create
visibly detectable plumes, depending on the volume of the discharge. It is difficult to
predict what a detectable volume of discharge would be and whether this would lead to
community concerns. The discharge would be constant throughout the rainy season and
correcting it after construction is completed may be difficult.
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Strander Grade Separation Phase 3 Page 8 of 68
The insoluble iron can also coat the walls of pipes and pump systems, causing long-term
maintenance concerns. During construction, the inside pipes of the dewatering pump
system became partially clogged with this material. See Figure 4 below.
Figure 4. Construction Dewatering Pipes
Recently, the design team has been collecting water samples from the underdrain
cleanouts and downstream catch basins to monitor the effects of the iron on the system.
The underdrain pipes are connected by sumpless Type 1 catch basins that serve as
cleanouts to facilitate the removal of any accumulated material. The insoluble iron is
collecting in these structures and the underdrain system. See Figure 5 of iron
accumulation in a cleanout.
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Strander Grade Separation Phase 3 Page 9 of 68
Figure 5. Underdrain System Cleanout
Water samples from the cleanouts contain high concentrations of the insoluble iron.
Below are two pictures of the same water sample. The first was taken at the project site
(Figure 6).
Figure 6. Underdrain Water Sample
The second was taken at the office a few days later (Figure 7). As can be seen, the
insoluble iron settles out to the bottom but also coats the inside of the container.
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Strander Grade Separation Phase 3 Page 10 of 68
Figure 7. Underdrain Water Sample Settling
The underdrain and storm system were designed as a flow through system without
water surcharging the system. Post-Phase 2 construction, the water levels in the wetwell
were reconfigured to reduce the daily pump cycles. This has caused the system to be
surcharged. The most notable aspect of this is that the iron laden water is backflowing
into the storm pipes. Potentially, this is increasing the long-term maintenance of the
storm system. However, the water sample taken from the storm structure closest to the
wetwell had significant less insoluble iron. See Figure 8.
Figure 8. Storm System Water Sample
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Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 11 of 68
There is a 2-foot sump in the storm structures. The cleanouts do not contain a sump. The
sumps allow the congealed insoluble iron to deposit at the bottom while the cleaner
water passes through the system.
The presence of iron-laden water is problematic in domestic well water systems. These
types of systems use shock chlorination to kill the iron bacteria that are present in the
well. It does not prevent the long-term reintroduction of bacteria into the system.
2.6 Wetlands
There are numerous wetlands in the project vicinity. David Evans and Associates
prepared a Wetland Technical Memorandum (WTM) for the City of Renton in
November 2007. The main body of the above-mentioned memo is located in
Appendix B.
This document describes the wetlands in the project area. This document also discusses
impacts to the wetlands, which were based on a previous roadway configuration. The
impacts that are discussed in the WTM do not apply to the current Strander Boulevard
extension project. An exhibit showing potential impacts as a result of Phase 3 are
included in Appendix C. A portion of the wetlands was filled in the vicinity of the BNSF
embankments, as part of the previous phase of the project. The Phase 3 project will
impact Wetlands O, N, and a portion of Q/R. Wetland impacts will be mitigated.
One of the largest wetlands in the project vicinity is Wetland Q/R (Figure 9). This
wetland consists of Wetlands Q and R and is referred to as Wetland Q/R. Wetland Q/R is
located south of the extended Strander Boulevard on the Tukwila property between the
two rail lines. This wetland encompasses approximately 25 acres and is considered
Category I/II Wetland per Ecology rating system. There is a 36-inch culvert at the north
end of Wetland Q/R. This culvert conveys water from Wetland Q/R to the east under
BNSF.
Wetlands A, B, C, D, and E are located between the UPRR tracks and the Interurban
Trail. According to the WTM, these wetlands are classified as Category III. These
wetlands are wet in the wet season and dry in the summer season. Wetlands A, D, and E
are hydrologically isolated, meaning that any stormwater that reaches them is trapped.
Wetland C is hydrologically connected to Wetland B in the wet season as the water
levels in the wetlands rise. The project will not impact Wetlands A, B, C, or D. Wetland B
is connected to Wetland Q/R by a 36-inch culvert that runs west to east under the UPRR
embankment.
Springbrook Creek Wetland and Habitat Mitigation Bank is located on the east side of
BNSF and south of Bank of America building (Figure 10). The 130-acre mitigation bank
was created to provide compensation for unavoidable wetland impacts caused by future
Washington State Department of Transportation (WSDOT) projects.
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Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 12 of 68
Figure 9. Wetlands Q/R, A, B, and portions of C (Wetlands D and E to south not shown)
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Figure 10. Springbrook Creek Wetland and Habitat Mitigation Bank
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Strander Grade Separation Phase 3 Page 14 of 68
3.0 PHASE 3 GROUNDWATER VOLUMES
3.1 Introduction
Shannon & Wilson performed subsurface explorations and installed groundwater
observation instruments to evaluate the subsurface conditions and provide permanent
dewatering and stormwater pumping requirements for the planned Phase 3 expansion
at the Strander Boulevard project in the city of Tukwila, Washington. The field
explorations identified soil conditions that are generally similar to those encountered
during earlier phases of the project; these conditions consist of a 30-foot-thick unit of
relatively low permeable silt, clay, and organic overbank soils (He unit) overlying at
least 30 feet of poorly graded alluvial sand (Ha unit). The upper unit contains shallow,
perched groundwater less than 10 feet below grade, and the groundwater in the
alluvium is typically 15 to 20 feet below grade. Temporal changes in groundwater are
influenced by the nearby Green River.
3.2 Overview of Conceptual Site Model
To support the Phase 3 system design, Shannon & Wilson also developed a 3-D
groundwater flow model to estimate groundwater inflows to the planned Phase 3
underdrain system and the infiltration potential for the Phase 3 stormwater pond. The
development of this model involved the following steps.
1. Developing a conceptual site model (CSM) for the project site and surrounding
area.
2. Building the model using the United States Geological Survey’s code MODFLOW-USG1
and the graphical-user interface program GMS version 102 based on the CSM.
3. Calibrating the model to reasonably reproduce historic data (recorded
groundwater levels and pumping station flows).
4. Simulating the planned Phase 3 underdrain and stormwater pond systems to
predict groundwater inflow and infiltration rates under three hydrologic
conditions.
Shannon & Wilson also evaluated a series of discharge mitigation options to reduce the
volume of water to be managed by the Phase 3 groundwater system. The following is a
summary of the development, calibration, and use of the model to perform predictive
simulations of the Phase 3 stormwater system.
1 Panday, Sorab; Langevin, C. D.; Niswonger, R. G.; and others, 2013, MODFLOW-USG version 1: An unstructured
grid version of MODFLOW for simulating groundwater flow and tightly coupled processes using a control volume
finite-difference formulation: U.S. Geological Survey Techniques and Methods 6-A45, 68 p/., available:
https://pubs.er.usgs.gov/publication/tm6A45.
2 Aquaveo, LLC, 2014, Groundwater modeling software GMS (v. 10.1): Provo, Utah, Aquaveo, LLC.
Final Draft Submittal BergerABAM, A16.0187.00
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Strander Grade Separation Phase 3 Page 15 of 68
The CSM was based on proposed Phase 3 project details and incorporated quantitative
components of local hydrology (surface water levels and precipitation-derived recharge)
and hydrogeology (aquifer/aquitard properties, groundwater levels and gradient,
discharge at the Phase 2 drain system).
Figure 11 shows the key water budget components of the drain inflow and pond
outflow computation, which are
1. Groundwater enters the underdrain system, and surface runoff (from precipitation
events) enters the stormwater drain system.
2. The combined groundwater and runoff drain system inflow is pumped to the
stormwater pond, assuming no losses.
3. In the pond, water infiltrates the relatively low permeable surficial soils,
evaporates, or overflows the pond weir to the wetlands (when the infiltration and
evaporative capacities are exceeded.)
Therefore,
Pond Overflow Rate = Combined Drain System Inflow – Infiltration – Evaporation
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Strander Grade Separation Phase 3 Page 16 of 68
Figure 11. Conceptual Water Budget for Phase 2 System
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3.3 Flow Model Development and Calibration
The model occupies an area 2,750 feet by 2,000 feet, is centered on the Strander project
area, and is hydrologically bounded to the west by the Green River and to the east by
the Springbrook Creek and wetlands. The model uses eight layers to represent the upper
100 feet of unconsolidated sediments and has computational cells with dimensions
ranging from 20 feet by 20 feet at the perimeter to 5 feet by 5 feet at the project area. The
model is able to explicitly calculate the groundwater inflow to the underdrain system
and the infiltration at the pond. The surface runoff inflow to the stormwater drains and
pond evaporation components are calculated separately.
The model includes a discrete high permeability area at the location of the BNSF bridge
foundations. This high permeability area represents the “window” that was excavated
through the He unit through to the underlying Ha unit during the construction of the
Phase 2 system as described Section 2.4. This window is believed to be a significant
conduit for deeper groundwater to enter the existing underdrains.
The CSM was calibrated to the following data sets.
1. The 24-hour constant rate pumping test performed for Phase 2 using well PW-1 in
2010 (Shannon & Wilson, 2011)3
2. The historical groundwater level and Phase 2 underdrain system discharge data
for the 21-month period from February 2015 through October 2016
Overall, the model adequately reproduced the observed pumping and discharge data as
illustrated in Figure 12. However, as shown in Figure 12, data from the existing pump
stations for the wettest portion of the 2015/2016 winter was corrupted and not useable
for the calibration effort. Additional calibration efforts using groundwater level and
underdrain inflow data from the 2016/2017 winter season will be used to improve the
confidence in the model.
Appendix A contains additional detailed information about the model development and
calibration.
3 Shannon & Wilson, Inc., 2011, Strander Boulevard Underpass Phase II, revised dewatering evaluation: Report
prepared by Shannon & Wilson, Inc., Seattle, Wash., 21-1-21292-003, for BergerABAM, Federal Way, Wash., May.
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Strander Grade Separation Phase 3 Page 18 of 68
Figure 12. Transient Calibration Results – Phase 2 Underdrain Groundwater Inflow
Note: Data collection
started February 2015
Recorded drain inflow data missing
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Strander Grade Separation Phase 3 Page 19 of 68
3.4 Predictive Simulations
The calibrated model was used to simulate the expanded Phase 3 underdrain and
stormwater pond system for three hydrologic conditions (each run at steady-state).
These conditions are
1. Average annual hydrology – average precipitation-derived recharge, equal to
6 inches per year; a midyear Green River stage of Elevation 14 feet; and an eastern
boundary groundwater level of Elevation 16 feet
2. Normal winter – typical winter Green River stage (Elevation 20 feet); and eastern
boundary groundwater level (Elevation 18 feet)
3. Wet winter – high winter Green River stage (Elevation 23 feet); and eastern
boundary groundwater level (Elevation 20 feet)
Table 1 summarizes the predicted water budget for the Phase 3 underdrain and
stormwater pond system for the three hydrologic conditions for the Base Case. The total
inflow to the Phase 3 drain system is equal to the groundwater inflow (calculated by the
model) and estimates for surface runoff for an average annual precipitation of 36 inches
(equal to 10 gpm on average and 60 gpm in the wet winter season). Note that the peak
roadway runoff during storm events is larger than these seasonal averages. Peak runoff,
combined with the limitations of storage volume in the wet well for the pump system,
results in a required pumping capacities of approximately 6,600 gpm in the 100-year
storm event, as described in Section 5.1.
The model predicts that the groundwater inflow to the Phase 3 underdrains would be
between 150 gpm (average annual conditions) and 355 gpm (wet winter conditions).
Assuming that the total inflow to the pump station is conveyed to the stormwater pond,
the estimated overflow from the pond to the wetlands and channel is expected to be
between 130 gpm (average annual conditions) and 405 gpm (wet winter conditions).
This overflow rate is between 10 and 50 percent higher than for the existing Phase 2
system under the same hydrologic conditions.
Table 1. Water Budget for Stormwater Pond – Phase 3 Base Case
Hydrologic Case
Phase 3 System
(GW + Runoff)
{A}
Evaporation Loss at
Pond
{B}
Infiltration at Pond
{C}
Estimate Overflow
from Pond
{D = A-B-C}
Average annual 160 (150 + 10) 5 25 130
Normal winter 285 (255 + 30) 0 15 270
Wet winter 415 (355 + 60) 0 10 405
Notes: Units are gpm; GW = groundwater; Runoff estimated using the Rational Method and precipitation data for Feb. 2016 to Oct. 2016.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 20 of 68
3.5 Flow Mitigation Options
The model was also used to evaluate the potential to reduce the groundwater inflows to
the Phase 3 underdrain system and/or limit overflows from the stormwater pond. The
four concepts considered are
1. Case A – remove the overexcavated window through the He unit in the Phase 2
excavation by grouting.
2. Case B – install low permeability cutoff walls through the He unit and partially
through the upper part of the Ha unit.
3. Case C – re-inject water collected at the pump station in recharge wells located
around the stormwater pond perimeter.
4. Case D – combine Cases A and C.
Case A involved assuming the overexcavated window through the base of the He unit
could be eliminated by grouting. In practice, this would likely involve removal of some
of the existing structures. This case was run for all three hydrologic conditions.
Case B involved installing impermeable sheet walls around the northern, eastern, and
southern ends of the Phase 2 underdrain where the overexcavation took place. The goal
of this action was to reduce inflow from the Ha unit. Three wall depths were simulated,
one each extending from ground surface to Elevations -5 feet, -25 feet, and -50 feet. This
case was run for only the average hydrologic condition.
Case C involved simulating six shallow groundwater wells that re-inject water removed
at the pump station as a means to reduce (or eliminate) the overflow from the pond. This
case was run for all three hydrologic conditions.
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Strander Grade Separation Phase 3 Page 21 of 68
Table 2 summarizes the predicted water budget results for these mitigation cases.
Figure 13 shows the predicted groundwater inflow to the existing (Phase 2) and new (for
the Phase 3 system) underdrains for the Base Case and four mitigation option cases.
Figure 14 shows the predicted total groundwater inflow to the Phase 3 underdrain
system and the estimated net overflow from the stormwater pond to the wetlands for
each case.
Table 2. Estimated Water Budget for Phase 3 Mitigation Cases
Hydrologic
Case
Expanded
Phase 3 System
Case A
Grout Window
Case B
Cutoff Wall
Case C
Recharge Wells
Case D Combined Grout
Window and Recharge
GW
Inflow
Pond
Overflow
GW
Inflow
Pond
Overflow
GW
Inflow
Pond
Overflow
GW
Inflow
Pond
Overflow
GW
Inflow
Pond
Overflow
Average
annual 150 135 50 35 130-
1501
115-
1301 180 5 70 0
Normal
winter 255 270 90 105 NA NA 310 35 NA NA
Wet
winter 355 405 115 165 NA NA 385 45 NA NA
Notes: 1 Range for three modeled wall depths; Units are gpm; NA = not analyzed
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Strander Grade Separation Phase 3 Page 22 of 68
Figure 13. Model-Predicted Groundwater Inflow to Phase 3 Underdrain System
Notes: Case A – remove Phase 2 construction “window” Case B – cutoff wall (average annual hydrology only) Case C – recharge wells Case D – combined Cases A and C (average annual hydrology)
Final Draft Submittal BergerABAM, A16.0187.00
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Strander Grade Separation Phase 3 Page 23 of 68
Figure 14. Model-Predicted Overflow from Phase 3 Stormwater Pond
Notes:
Case A – remove Phase 2 construction “window”
Case B – cutoff wall (average annual hydrology only)
Case C – recharge wells
Case D – combined Cases A and C (average annual hydrology)
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Strander Grade Separation Phase 3 Page 24 of 68
The results of these studies indicate the following.
1. For Case A, grouting the window through the relatively low permeability He unit,
the groundwater inflow to the Phase 3 underdrains would be between 50 gpm
(average) and 115 gpm (wet winter). The estimated pond overflow rates are
35 gpm and 165 gpm, which are 25 and 40 percent of those predicted for the
Base Case.
2. For Case B, the cutoff wall options would have minimal effects on groundwater
inflows to the Phase 3 system. This option would only be beneficial if the wall
could be keyed into a low permeability soil unit to reduce vertical flow from the
lower part of the Ha unit.
3. For Case C, the six recharge well option could theoretically greatly reduce the
overflow from the stormwater pond (despite increasing the groundwater inflow to
the pumping system by between 10 and 20 percent). However, there would be
significant practical challenges in operating and maintaining these wells.
4. The hybrid Case D would reduce the required recharge rate for each well from
165 gpm (for Case C) to 55 gpm for the average hydrology condition. This would
make this option more practically feasible.
The high wet season hydrologic condition for the Base Case was simulated using a
revised version of the calibrated model that represented a conservative set of key
parameters (specifically, higher He and Ha unit permeabilities and underdrain
conductance values) based on a sensitivity analysis presented in Appendix C of Shannon
& Wilson’s Hydrogeologic Report included as Appendix A to this report. The results
indicated that the groundwater inflow to the Phase 3 underdrain system would be
500 gpm, which is 40 percent higher than for the 355 gpm predicted for the calibrated
Base Case.
3.6 Preliminary Recommended Design Flows for an Unsealed (non-watertight)
Underpass
There is some uncertainty predicting the design flow for the Phase 3 project if it were to
be constructed without a watertight bottom seal and walls. Those uncertainties are
primarily related to the following issues.
1. Variations in actual, in-situ, soil properties from those assumed in the
groundwater model.
2. Effectiveness of any flow mitigation efforts used.
3. Uncertainties in predicting the combination of winter weather and peak storm
events that should be used.
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Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 25 of 68
For the purpose of estimating the inflow of groundwater into an unsealed underpass,
the following conditions were assumed.
1. The in-situ soil properties are accurately reflected in the groundwater model.
2. The only flow mitigation measure to be implemented would be to grout the
“window” excavated through the low permeability He unit at the BNSF bridge
foundation.
3. Peak winter inflows would be used as a design condition. These flows are about
20 percent higher than the average winter inflows.
The effective design groundwater flow would then depend on the effectiveness of the
proposed flow mitigation measures. It is likely that the grouting around the BNSF
bridge foundation will be highly effective in reducing groundwater inflows. Conversely,
it is very unlikely that the grouting would be totally ineffective. Therefore, an upper and
lower bound on groundwater inflow was established by considering the following two
conditions.
1. If grouting of the “window” excavated through the He unit at the BNSF bridge
foundation is 100 percent effective, it would reduce the peak winter groundwater
inflows to the stormwater system by 240 gpm from 355 gpm to 115 gpm as
illustrated in Figure 13.
2. If grouting of the “window” excavated through the He unit at the BNSF bridge
foundation is only 25 percent effective, the peak winter ground water inflows to
the stormwater system would be reduced by only 60 gpm from 355 gpm to
295 gpm.
For the purpose of this study, a groundwater inflow of 355 gpm was used. Designing for
355 gpm provides adequate system reserve capacity should more permeable subsurface
soils be encountered and/or more extreme weather events occur and/or the grouting of
the “window” through the He layer is not 100 percent effective. Alternatively, a more
rigorous, probability-related analysis would need to be performed during final design to
arrive at a design flow.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 26 of 68
4.0 IMPLICATIONS OF NEW STORMWATER STANDARDS
The KCSWDM has recently been updated to conform to the 2014 Ecology SMMWW. The
KCSWDM has been preliminarily approved by Ecology. The three biggest revisions to
the upgraded manuals are (1) the wetland hydroperiod criteria, (2) mandatory flow
control best management practices (BMPs) implementing Low Impact Development
(LID) strategies, and (3) stricter flow control modeling criteria known as the LID
Performance Standard.
4.1 Wetland Hydroperiod Criteria
A wetland hydroperiod is the seasonal pattern of water level in a wetland and is
determined by the frequency and extent of inundation occurring throughout the year.
Because hydrology is probably the single most important determinant of the
establishment and maintenance of specific types of wetlands and wetland processes,
changes to a wetland’s hydroperiod resulting from the construction of the project need
to be controlled and minimized.
The new standard accomplishes this by comparing the volumes of inflow for the pre-
project and post-project scenarios. Daily volumes and monthly volumes are calculated
using a continuous runoff model that inputs 50 years of precipitation data. The 50-year
values are then averaged to produce 365 daily volumes and 12 monthly volumes. The
new standard required that the following two conditions be met.
1. The post-project daily average volumes cannot increase or decrease by more than
20 percent from the pre-project daily volumes
2. The post-project monthly average volumes cannot increase or decrease by more
than 15 percent from the pre-project monthly volumes
In the previous 2005 standard, it did not consider the volume of water, but instead
required an analysis of fluctuations in the wetland water level for depth, frequency,
duration, and during the dry period. This earlier methodology was size dependent,
meaning if a wetland was large, runoff would have less of an impact than to a smaller
wetland. The same flow over a larger area would produce less water level fluctuations.
The latest standard does not take into account the size of the wetland and only analyzes
the net inflow. The anticipated net inflows for the Phase 3 project will exceed the
amounts described above. Because of this, the Phase 3 project cannot discharge water to
the adjacent Wetland Q/R and will require that an alternative outfall location be used.
Potential outfall locations are discussed in Section 5.4, Outfall Location.
In Phase 3, the same volume of water will be routed to the wetland as was previously
routed prior to Phase 2, within the limits specified in the new standard for conditions
No. 1 and No. 2 described above. This will be accomplished through a secondary outlet.
The location of the outlet will vary slightly by alternative as discussed in Section 6.0,
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 27 of 68
Storm System Build Alternatives. The sizing methodology is atypical and is discussed
further below.
Prior to the construction of Phase 2, the tributary area to Wetland Q/R was 53.93 acres,
7.84 acres of this area contains the project footprint. Project footprint areas are included
in Appendix E. The volume of water produced by the 53.93 acres is considered the
wetland predevelopment condition. An outfall to the wetland will replicate the
predeveloped condition. The wetland outlet will consist of a single orifice control
structure. This structure will work in tandem with a control structure that outlets to the
river and is also located in the water quality facility. The river outlet will consist of a
control structure with two orifices. The lower orifice will convey flows up to the
groundwater flow rate. Flows greater than the groundwater flow will trigger the orifice
in the wetland outlet. As the water levels approach the wetland predeveloped condition,
the second orifice in the river outlet is triggered. Groundwater and all flows greater than
the wetland predeveloped condition will be routed to the river.
4.2 Mandatory Flow Control Best Management Practices
The primary intent of requiring flow control BMPs is to mitigate hydrological impacts of
increases in impervious surfaces. Increases in impervious surfaces increase peak flows,
increase the volume of water reaching downstream water bodies and reduce pervious
surfaces that provide groundwater recharge. By implementing flow control BMPs on a
project, the size of detention facilities are reduced.
The following are 11 flow control BMPs.
FC BMP 1 – Full Dispersion
FC BMP 2 – Full Infiltration
FC BMP 3 – Limited Infiltration
FC BMP 4 – Basic Dispersion
FC BMP 5 – Farmland Dispersion
FC BMP 6 – Bioretention
FC BMP 7 – Permeable Pavement
FC BMP 8 – Rainwater Harvesting
FC BMP 9 – Reduced Impervious Surface Credit
FC BMP 10 – Native Growth Retention Credit
FC BMP 11 – Perforated Pipe Connection
Per the KCSWDM, if a project cannot incorporate any of the flow control BMPs, the
project must document why the BMP cannot be met. BMPs 1 through 8 and 11 lessen the
impacts of a project by infiltrating a portion of the runoff, through various methods, into
the ground. These nine BMPs are infeasible for this project site because the runoff would
continually be infiltrated, enter the groundwater, and enter the underdrain system to be
once again pumped to the surface.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 28 of 68
For BMP 9, Reduced Impervious Surface Credit, a credit is given if a project can reduce
its impervious footprint by either using wheel strip driveways, reducing the building
footprint from zoning requirements, providing open grid decking for paths or parking,
or elevating a building so that additional runoff storage is provided in the soil
underneath the building. None of these are applicable to the project. The last BMP 10,
Native Growth Retention Credit, applies to a project that preserves a portion of the
native vegetated surfaces. The project site was previously cleared, decades ago, and does
not contain any native vegetated surfaces; therefore, is not applicable to this project.
4.3 LID Performance Standard
The intent of the LID Performance Standard is to mitigate the small storms (less than
two-year storm) that are not captured in the flow control standard. The LID
Performance Standard requires that projects outside of the Urban Growth Area (UGA)
must match postdeveloped discharges to predeveloped discharges for 8 percent of the
two-year flow up to 50 percent of the two-year peak flow when modeling flow control
facilities. This additional requirement increases the sizes of detention facilities because it
further decreases the allowable postdevelopment discharge rate. The project is inside the
UGA; therefore, the requirement is not triggered.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 29 of 68
5.0 OVERVIEW OF STORMWATER SYSTEM COMPONENTS
The project is bounded to the south by Wetland Q/R. There is approximately 2.5 acres
available between the southern limits of the project and the wetland to construct both
the water quality and detention facilities. This limits what treatment and detention
facilities can be incorporated into the project. There are five main components to the
stormwater system. They are
1. Pump Station System(s)
2. Water Quality Facility
3. Detention Facility
4. Outfall Location
5. Discharge Route
There are multiple options for each of the components. The sections below describe each
of the options, their purpose, advantages, disadvantages, long-term maintenance, and
cost. The cost is a labor and material cost and does not include programming costs. The
options for each component have been used to develop the build alternatives described
in Section 6.0, Storm System Build Alternatives.
The conveyance and underdrain systems for the roadway are identical for each of the
alternatives and are not discussed in this memo.
5.1 Pump Station System(s) Options
5.1.1 Introduction
The configuration of pump station system options is dependent on whether the
groundwater and stormwater flows will be pumped separately or combined. In either
case, the existing pump station will need to be upgraded to convey approximately
6,600 gpm of stormwater, required to convey the 100-year storm event and have
100 percent redundancy. The existing rated firm pumping capacity, with 100 percent
redundancy, by a secondary pump, is approximately 3,300 gpm. The existing total
pumping capacity, with no redundancy, is approximately 6,000 gpm. The existing pump
station is described in further detail in Section 5.1.2 below.
An upgrade to the existing pump station may be avoided if flow metering data can be
obtained upstream of the pump station. Metering of both the stormwater and
groundwater is needed upstream of where they are combined. This data could provide a
basis for establishing a lower design flow. Alternately, the City could accept the risk of
the 100-year storm occurring at the same time a pump fails. The probability of these two
events occurring simultaneously is low. So, for example, the pump station could be
designed for the 100-year flow with 100 percent redundancy and use both pumps to
handle the 100-year storm with no redundancy. For the purpose of this study, it was
assumed the existing pump station would be upgraded to handle the estimated inflows
from a 100-year storm with 100 percent redundancy.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 30 of 68
If the flows are pumped separately, an additional new pump system will be required for
the groundwater. This option is presented below in Section 5.1.3, Separated
Groundwater and Stormwater Flows. If the flows are combined, the existing pump
system will still need to be upgraded to convey the 100-year storm event as described
above. This option is presented below in Section 5.1.4, Combined Groundwater and
Stormwater Flows.
Whether or not the underpass is sealed, the pumping capacity for the upgraded existing
pump station will be the same because the groundwater flows are a small proportion of
the stormwater flows from the 100-year event. Groundwater flow is estimated to be as
high as 355 gpm of groundwater if the underpass is not sealed. An estimate of
groundwater flow for a sealed underpass has not been made, but based on previous
experience from the watertight underpass at South 180th Street, the groundwater flows
will likely be around 25 gpm.
5.1.2 Existing Pump Station
Below is a schematic of the existing pump station system (Figure 15). The stormwater
and groundwater are combined and are conveyed to an inlet manhole.
The existing pump system receives combined stormwater and groundwater from the
existing roadway storm drains and underdrain system. The flows combine at a manhole
prior to entering the pump station inlet manhole via a 36-inch-diameter inlet line. Flow
then enters the wetwell, which contains two 50-hp solids handling submersible pumps.
Each pump is rated for the current 100-year storm flow rate and an allowance for
groundwater totaling approximately 3,300 gpm. In the event one pump fails, the
remaining pump can handle 100 percent of the required flow.
The pumps operate based on water levels in the wetwell. One pump cycles when the
level reaches the “Lead Pump On” elevation and turns off when the level is drawn
down to the “Pumps Off” elevation. The pumps alternate operation so that during the
next cycle the previously resting pump activates first. The level settings include a “Lag
Pump On” so the second pump cycles on if the level in the wetwell continues to rise
after the lead pump starts running. The “lead on” and “pumps off” levels are set at the
inlet pipe crown and invert respectively so the volume of water pumped during each
cycle includes that stored in the wetwell and inlet pipe.
A check valve and isolation valve are installed in each discharge line to prevent
backflow into the wetwell and to isolate each pump for maintenance. The discharge
lines are manifolded together prior to the force main. The manifold and valves are
located in a below-ground valve vault next to the wetwell. The wastewater is then
conveyed through a meter vault where the flow is recorded and totalized before
discharging to the flow splitter via a 24-inch-diameter force main.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 31 of 68
Other components of the pump station include a building, which houses the motor
control center, programmable logic controller (PLC), telemetry equipment, and
disconnect panels. A 175-kilowatt (kW) standby generator in an outdoor enclosure
provides backup power. A load bank is connected to the generator for periodic turnover.
The pump station PLC signals alarms to the City via telemetry if high or low levels,
overflows, pump failure, or loss of primary power occurs.
Figure 15. Schematic of Existing Pump Station System
5.1.3 Separated Groundwater and Stormwater Flows
As discussed in Section 2.2, the groundwater and stormwater flows are separate systems
until the lines connect downstream. For the option, this downstream connection will be
reconfigured so that the flows will remain separated and will each contain their own
pump stations.
The new groundwater pump system will require converting manhole DR-12 to a
wetwell, installing two 5-hp submersible pumps in the wetwell, valves and discharge
piping for the new pumps, new valve vault to house the valves, local controls housed in
a NEMA 4 outdoor enclosure, power connection to the existing controls building,
reconfiguring the existing PLC, and replacing the telemetry panel at an approximate cost
of $300,000 (Figure 16).
BLDG = Building
GEN = Generator
GW = Groundwater
IM = Inlet manhole
LB = Load bank
MV = Meter vault
Storm = Stormwater
VV = Valve vault
WW = Wetwell
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 32 of 68
Figure 16. Groundwater and Upgraded Stormwater Pump Stations
The minimum requirements for the upgraded stormwater pump station include the
addition of a third 60-hp pump in the existing wetwell, new 14-inch impellers and 60-hp
motors for the two existing pumps, reconfigured discharge piping and valve vault, new
wetwell lid and access hatch, expanded MCC, reprogrammed PLC, and replacement
telemetry panel. It may also be necessary to expand the standby power system by
adding a second generator or replacing the existing generator with a larger unit.
Because the manufacturer of the existing pumps has discontinued the currently installed
model and will not warranty replacement impellers and motors, consideration should be
given to replacing the existing pumps with new pumps that are more efficient and better
suited to the new duty point. Replacing the pumps will negate the need to expand the
existing standby power system. The budgetary cost of upgrading the existing pump
station is $650,000. This includes either all new pumps, or modifying the existing pumps
with the addition of a third pump and replacement generator.
Each pump system will also require an energy dissipater prior to the groundwater
entering the water quality facility and the stormwater entering the detention facility. An
energy dissipater reduces the velocity of the flows from the pump station, which protect
downstream erosion of stormwater facilities.
BLDG = Building
GEN = Generator GW = Groundwater
IM = Inlet manhole LB = Load bank
MV = Meter vault
Storm = Stormwater VV = Valve vault
WW = Wetwell
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 33 of 68
Energy dissipaters come in a variety of shapes and sizes. They may be enclosed or open.
Below is an example of an open energy dissipater (Figure 17). In this structure, the high-
velocity concentrated flows impact the vertical wall, which dissipates the energy.
The configuration of the energy dissipater will be determined during final design.
Figure 17. Energy Dissipator
5.1.4 Combined Groundwater and Stormwater Flows
If the flows are combined, the cost for the upgrades to the existing pump station system
is the same as for the upgraded stormwater pump station ($650,000) described above
because the groundwater flow is negligible compared to the 100-year stormwater flow.
The groundwater flows would be routed to the water quality facility. Stormwater flows
would be routed to the detention facility. A flow splitter would be required to
accomplish this. A single structure could be used to provide both energy dissipation and
also serve as a flow splitter. This configuration is illustrated in Figure 18 below.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 34 of 68
Figure 18. Single Structure Configuration to Provide Energy Dissipation and Serve as Flow Splitter
5.1.5 Evaluation of Pump Station Options
When the groundwater and stormwater are kept as two separate systems, an additional
pump station is required to pump the groundwater. This will increases initial capital
costs, annual operating and maintenance costs, and life-cycle costs of the system.
However, this additional groundwater pump station will not be large and will be the
same whether the underpass is sealed or not. Keeping the groundwater separate from
the stormwater will also simplify the design of the detention and treatment systems
because the actual volume of ground water inflows, and its seasonal variation, cannot be
known with certainty until after the facility is constructed.
5.2 Water Quality
5.2.1 Treatment Requirements
The minimum water quality standard is termed basic treatment. The goal of basic
treatment is to remove 80 percent of the total suspended solids for flows or volumes up
to the water quality design flow or volume for a typical rainfall year.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 35 of 68
Enhanced treatment facilities remove 30 and 60 percent or more of dissolved copper and
zinc, respectively. Enhanced treatment does not provide a higher level of basic
treatment. It broadens what is treated.
Per Section 1.2.8.1 of the KCSWDM, if 50 percent or more of the runoff directed to a
water quality facility is from a roadway with an expected average daily traffic count of
2,000 or more vehicles, then enhanced water quality is required. Enhanced treatment is
also required if a project discharges to a wetland.
However, per the last paragraph on page 1-72 of the KCSWDM, projects that drain
entirely by pipe to major receiving waters may revert to the basic water quality
treatment standard as long as it is not an impaired waterbody. This project will
discharge by pipe to the Green River. However, the project also discharges to a wetland,
therefore, enhanced treatment is required.
5.2.2 Sizing and Flow Rate Considerations
Water quality facilities are sized for either a flow rate or volume, depending on the type
of water quality facility. If sizing is based on flow rate, the water quality flow rate will
vary whether the facility is upstream or downstream of the detention facilities. If the
facility is upstream of detention, then the water quality flow rate is the rate at which
91 percent of the total runoff volume will be treated using a continuous model and a
15-minute time step. When the water quality facility is downstream, the full two-year
release rate of the detention facility is used. The water quality volume is estimated using
a 24-hour storm with a six-month return frequency.
If groundwater is combined with stormwater, meeting flow control requirements for the
adjacent wetland will be more difficult, particularly because the exact rate of
groundwater flow, and its seasonal variation, will not be known until the facility is
constructed and been in operation for at least a year. Post-construction adjustments to
orifices and flow control devices may be required.
The three types of water quality facilities considered for use on this project were a wet
biofiltration swale, a constructed wetland, and a biofiltration pond. Each of these is
described in the subsections below.
5.2.3 Wet Biofiltration Swale
A biofiltration swale is a long gently sloped grass ditch that is designed to settle out
pollutants from stormwater. On sites with low soil permeability, a high water table or
continuous base flow creates saturated conditions in the swale and the grass cannot
survive. In these conditions, wetland plants are used instead of grass, and the facility is
considered a wet biofiltration swale.
The wet biofiltration swale is approximately 200 feet long, has a bottom width of 20 feet,
and a total depth of 0.82 foot. A maximum ponding depth of 4 inches will be provided to
ensure the wetland plants are not inundated with water. Side slopes will be constructed
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 36 of 68
at a 3H:1V or less. Due to poor site soils, compost-amended soils will be tilled into the
native soils to a depth of 18 inches. Underdrains will not be required because the
longitudinal slope is greater than 1.5 percent. Access will be provided at the beginning
and end of the wet biofiltration swale. Stormwater will exit the wet swale via a pipe set
at the water quality surface elevation.
The swale will be sized to convey the two-year release rate from the detention pond. The
groundwater flow can be incorporated into this facility if the groundwater and
stormwater flows are pumped together. Preliminary sizing of the wet biofiltration swale
was based on the anticipated two-year release rate of 47 gpm from the detention pond
along with the maximum groundwater rate of 355 gpm from unsealed underpass. The
swale will also act as a conveyance system for higher flows; therefore, a high flow
bypass pipe is not needed.
Figure 19. Biofiltration Swale Section
The biofiltration wet swale is an inexpensive facility with minimal maintenance.
Maintenance activities may include removing sediment deposited at the head of the
swale if the plant growth is being inhibited for more than 10 percent of the length or
regrading the bottom as needed if erosion develops. None of the maintenance activities
involve special tools or equipment. The vegetation will provide a higher level of iron
removal than grass.
5.2.4 Constructed Stormwater Wetland
A constructed stormwater wetland is a shallow pond that uses the biological plant
processes and the microbial community within the soils to remove pollutants. The pond
consists of two cells. The first cell acts as a settling basin, provides a foot of sediment
storage, and shall have a minimum depth of 4 feet. The second cell provides additional
pollutant removal. The depth of the second cell varies from 1 to 3 feet with an average
depth of 1.5 feet. This ensures the plants survival.
The sizing of a constructed stormwater wetland is similar to a water quality pond also
known as a wetpond. Because the depth of the second cell of a stormwater wetland is
shallower than a wetpond, and if the wetland were to treat the same volume of water,
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 37 of 68
the stormwater wetland would occupy a larger area than a wetpond to treat the same
volume of water.
The stormwater wetland pond will be irregular shaped to best use the available area and
will encompass approximately 24,000 square feet with 3H:1V side slopes. Stormwater
will exit the wetland pond via a jailhouse weir set at the water quality surface water
elevation.
Figure 20. Constructed Stormwater Wetland Section
This facility will have minimal short-term maintenance costs. Long-term maintenance
activities may include replanting and applying compost-amended soils to the second
cell to provide nutrition for the aquatic plants. This is the same for any facility with soil
amendments. This facility provides enhanced treatment and is more aesthetically
pleasing than other types of ponds. The constructed wetland acts as a stilling pond that
allows solids and the insoluble iron to drop out. This provides a higher level of iron
removal than the biofiltration wet swale.
5.2.5 Bioretention Pond with Underdrain
The bioretention pond is an engineered treatment and infiltration system that mimics a
forest floor. These types of facilities consist of planted shallow depressions with
amended or engineered soils. The soils are designed to filter and absorb water. The
plants aid in pollutant removal. Water will not be allowed to pond for more than
48 hours and will have a maximum ponding depth of 6 inches. Side slopes will be
constructed at a 3H:1V or less. An underdrain system below the pond allows the runoff
to infiltrate through the soils.
This facility is atypical but has been used by other municipalities, such as the City of
Bellevue.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 38 of 68
Figure 21. Bioretention Pond Section
This facility will need to initially be monitored after storm events to ensure that the
water is not ponding beyond the maximum depth. This would affect plant
establishment. This facility is considered a LID strategy and provides a higher level of
water quality treatment than the wet biofiltration swale or constructed wetland pond.
Furthermore, as the water percolates through the soil, the insoluble iron would likely be
removed. Although experience with this type of facility is limited, it has the potential to
provide the highest level of iron removal.
5.2.6 Evaluation of Water Quality Treatment Options
The water quality facilities were evaluated on their effectiveness in providing treatment,
their potential to provide insoluble iron removal, capital costs, and life-cycle
(maintenance) costs. The WSDOT Highway Runoff Manual (HRM) provides estimations
on the effective life, capital costs, and operation and maintenance (O&M) cost of water
quality facilities. This was taken into account in the ranking of the facilities.
Wet Biofiltration Swale. The wet biofiltration swale ranked the lowest with respect to
water quality. Biofiltration swales are not considered to provide enhanced treatment by
King County. However, other agencies do accept them and the proposed design
described here would provide enhanced treatment and would likely be accepted by
King County. Iron removal would be limited due to the constant flow of water through
the facility. The influx of water may reconstitute the iron. Per the HRM, the biofiltration
effective life is only 5 to 20 years, and the capital costs are low to moderate along with
the O&M costs.
Constructed Stormwater Wetland. The constructed stormwater wetland provides
enhanced water quality treatment and would provide better iron removal than the wet
biofiltration swale. This facility has a large permanent pool of water that acts as a stilling
basin and does not serve as a conveyance system as the swale does; therefore, it is not
expected that the iron sludge will get reconstituted. Per the HRM, this has a longer
effective life at 20 to 50 years, a moderate to high capital cost, and a moderate O&M
costs.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 39 of 68
Bioretention Pond. The bioretention pond with underdrain provides enhanced
treatment and provides the best potential for iron removal. The water will be cleaned as
it infiltrates through the engineered soils to be captured in the underdrain system. This
facility is the only one that provides oil control. This facility is atypical and is not listed
in the HRM. This facility works similarly to a bioinfiltration pond except that it contains
engineered soils and additional plantings. Per the HRM, a bioinfiltration pond has an
effective life of 5 to 20 years, a low to moderate high capital cost, and low O&M costs.
The low effective life is most likely related to the potential for plugging. The potential
for plugging would likely be greater considering the iron content of the groundwater.
5.3 Detention Facility
Detention facilities mitigate the impacts of storm and surface water runoff generated by
impervious surfaces that are a result of a project. If a project can outfall to a major body
of water, the project is exempt from providing detention, also known as flow control
exempt. The project will be discharging to the Green River. The Green/Duwamish River
is flow control exempt downstream of River Mile 6. The project will discharge upstream
of this location; therefore, it is not flow control exempt. The detention facilities will
conform to a Level 2 flow control standard. This standard matches developed discharge
durations to predeveloped durations for the range of the predeveloped discharge rates
from 50 percent of the two-year peak flow up to the full 50-year peak flow. The
detention facility will detain up to the 100-year storm event. The predeveloped condition
shall be considered forested.
The continuous modeling software, MGSFlood version 4.4, was used to complete the
flow duration analysis. Post-Phase 3, the project area of 7.84 acres will consist of
5.88 acres of impervious and 1.96 acres of pervious areas. Detaining back to forested
conditions requires approximately 1,062,000 cubic feet of storage for detention.
Detention facilities can be placed upstream or downstream of water quality facilities.
Due to site constraints, detention facilities will be placed upstream of the water quality
facilities.
5.3.1 Detention Pond with Walls
The detention pond will use vertical walls on all sides to minimize the footprint. This
allows water quality facilities to be constructed on the site without having to acquire
additional right-of-way. The pond footprint will encompass approximately
25,000 square feet and provide 5.5 feet of detention storage. An access road will be
provided around the pond for maintenance. As the project moves forward, an
emergency overflow and an access ramp will be incorporated into the design. The pond
will be lined with a low-permeability liner, such as compacted till liner, clay liner, or
geomembrane liner. An outlet control structure will meter the flow. The pond will outlet
into a water quality facility.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 40 of 68
Figure 22. Detention Pond with Walls Section
5.3.2 Detention Pond with 3H:1V Side Slopes
This detention pond will use 3H:1V side slopes rather than vertical walls. Water quality
facilities would need to be constructed off the site, which would require additional right-
of-way. The pond footprint is increased twofold and will encompass approximately
39,000 square feet with 2.7 feet of detention storage. An access road will be provided
around the pond for maintenance. As the project moves forward, an emergency
overflow and an access ramp will be incorporated into the design. The pond will be
lined with a low-permeability liner, such as compacted till liner, clay liner, or
geomembrane liner. An outlet control structure will meter the flow. The pond will outlet
into a water quality facility.
Figure 23. Detention Pond Section
5.3.3 Constructed Combined Wetland Pond
A constructed combined wetland pond provides both water quality and detention in one
facility. This option allows the stormwater wetland to be placed under the detention pond.
Figure 24. Combined Water Quality and Detention Pond Section
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 41 of 68
The stormwater wetland operates the same as if it were a stand-alone facility as
discussed in Section 5.2.4, Constructed Stormwater Wetland. The detention volume is
provided above the water quality surface.
The pond footprint will encompass approximately 39,000 square feet and provide
2.7 feet of detention storage. An access road will be provided around two sides of the
pond for maintenance. As the project moves forward, an emergency overflow and an
access ramp will be incorporated into the design. The pond will be lined with a low-
permeability liner, such as compacted till liner, clay liner, or geomembrane liner. An
outlet control structure will meter the flow.
By providing both water qualify and detention, this configuration occupies less space
and eliminates the need for the vertical walls in the detention facility. This in turn
reduces costs. Iron removal will be similar but less than for a stand-alone constructed
wetland. Based on observations of the water samples, the continual influx of storms into
the pond may provide enough motion for the iron to become resuspended.
5.3.4 Evaluation of Treatment Options
All of the detention facilities provide the same level of detention and are all considered a
wetpond. The difference between them is the geometry. Per the HRM, wetponds have
an effective life of 20 to 50 years, a moderate to high capital cost, and a low to moderate
O&M cost.
Detention Pond with Walls. The detention pond with walls will have higher capital
costs but minimizes the area needed for construction. This allows water quality facilities
to be constructed on the same parcel without the need for any additional property
acquisition. Maintenance is more cost-effective when the water quality and detention
facilities are close together. Therefore, given the property constraints of this project, a
detention pond with walls is considered the good option.
Detention Pond with 3H:1V Side Slopes. The detention pond that uses 3H:1V side slopes
rather than walls encompasses the majority of the parcel. This requires any separate
water quality systems to be constructed elsewhere. Therefore, this facility is not a good
option for this project.
Combined Wetland Pond. The constructed combined wetland pond provides detention
on top of the water quality facility. Its geometry is similar to the detention pond above,
using 3H:1V slopes. This system is an efficient use of space and good water quality
treatment. However, there are better ways to accomplish water quality treatment if
separate detention and water quality features are used.
5.4 Outfall Location
There are two existing outfalls within the project vicinity that could be upgraded to
serve the Strander Boulevard project. Either outfall will need to be upgraded, which will
require additional permitting. The Nationwide Permit 7 is required for waters of the
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 42 of 68
United States. Washington Department of Fish and Wildlife will require Hydraulic
Permit Approval. A City of Tukwila Critical Area Permit will also be required. Each of
these outfalls will need to be upgraded with a Tideflex valve to prevent fish entering the
outfall. An example of a Tideflex valve that the Strander project team designed and
constructed is included in Figure 25.
Figure 25. Tideflex Valve
5.4.1 Northern Outfall near Green River Bridge
The northern outfall is a corrugated metal pipe, located just south of the Strander
Boulevard Bridge that crosses the Green River. According to the 29 April 2016 Existing
Outfall Memorandum from Widener and Associates, this outfall is likely below the
horizontal and vertical limits of the ordinary high water. See Appendix D for the
Existing Outfall Conditions Memorandum.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 43 of 68
Figure 26. Northern Outfall
5.4.2 Southern Outfall Southwest of Substation
The southern outfall is located on the west side of West Valley Highway, approximately
150 feet southwest of the Puget Sound Energy substation. The outfall is approximately
25 feet downhill from the roadway. It is assumed that this outfall has additional capacity
because there is no scour beneath the outfall.
Figure 27. Southern Outfall
5.4.3 Evaluation of Outfall Locations
The northern outfall will require an upgraded outfall pipe with a Tideflex duckbill to
prevent fish passage up the pipe. This pipe is below the ordinary high water level;
therefore, any construction activities will need to occur within a fish window.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 44 of 68
The southern outfall appears to be above the ordinary high water level. The southern
outfall will also require a Tideflex duckbill, but construction activities that will need to
be performed on this outfall may not be constrained by a fish window. Therefore, the
southern outfall location is tentatively consider the preferred outfall location.
5.5 Discharge Route
There are two potential discharge routes to the Green River that are compatible with
either outfall. One route follows the proposed extension of Strander Boulevard under
the UPRR, remaining within the project’s right-of-way until it rises up again in the
vicinity of West Valley highway. The other route crosses under the UPRR south of
Strander. These two routes are shown in Figures 28 and 30, respectively. The route to the
south would require the City acquire easements to construction the discharge pipe. The
route that stays within the project right-of-way as it crosses under UPRR will require a
secondary discharge pump station for the stormwater and groundwater. See Figure 29
for configuration of the secondary discharge pump station.
5.5.1 Force Main Discharge Route within Strander Boulevard Right-of-Way
The discharge pipe will be located on the south side of the Strander Boulevard within
the public right-of-way. After passing under the UPRR, the discharge can be routed to
either the northern or southern outfall as shown in Figure 28.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 45 of 68
Figure 28. Discharge Routes within Strander Boulevard Right-of-Way
For the northern outfall, the stormwater will be conveyed to the west under State
Route 181 (SR 181), to an energy dissipator located in the parking lot on the southwest
corner of SR 181/Strander Boulevard. This route would require an easement from one
property owner. The drainage easement will require approximately 7,000 square feet.
For the southern outfall, the discharge pipe would also be located on the south side of
the proposed roadway but would turn south at the Interurban Trail to parallel the trail,
head west at the south end of the substation, to an energy dissipator located on private
property, turn south along the east side of SR 181 to the outfall location. This route
would require easements from three property owners. The three drainage easements
will require approximately 13,000 square feet.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 46 of 68
Figure 29. Secondary Discharge Pump Station
(Shown with groundwater and stormwater combined. Separated flows would be similar.)
A secondary pump station will incorporate the following major components.
12-foot-diameter wetwell
Two 100-hp pumps
18-inch discharge piping and valves
10-foot by 10-foot valve vault
Building to house MCC, PLC, telemetry equipment, and power distribution panel
300-kW dedicated on-site standby generator
The approximate cost of the new pump station is $1.8 million.
5.5.2 Gravity-Fed Discharge Route within Easements
For the northern outfall, the gravity-fed discharge pipe will convey the stormwater
under the UPRR embankment, through the Puget Sound Energy property, along the
northern edge of the substation, under SR 181 then head due north through the
aforementioned parking lot. This route would require easements from four property
owners. The four drainage easements will require approximately 18,000 square feet.
For the southern outfall, the discharge route is similar to the northern outfall except it
heads south at the Interurban Trail and continues on the same alignment as the previous
southern outfall route. This route would require easements from three property owners.
The three drainage easements will require approximately 12,000 square feet.
BLDG = Building
GEN = Generator GW = Groundwater
IM = Inlet manhole
LB = Load bank
MV = Meter vault
Storm = Stormwater VV = Valve vault
WW = Wetwell
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 47 of 68
See Figure 30 for the discharge routes within easements.
Figure 30. Discharge Routes within Easements
The available drop in elevations between the stormwater facilities and the outfalls is
minimal. Therefore, the slopes on the stormwater pipes will be less than 0.5 percent.
Ideally the pond could be raised to provide additional drop to the outfall. However, the
elevation of the discharge pipe is constrained by UPRR utility accommodation policy
that requires all non-flammable utility crossings, perpendicular to the railroad, to
contain a casing pipe, be located 4.5 feet beneath the base of the railroad rail and less
than 3 feet below bottom of ditches. This limits how high the discharge pipe could be
raised. Because of this, there does not appear to be an advantage to raising the treatment
facilities..
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 48 of 68
5.5.3 Evaluation of Discharge Routes
Routing the discharge within the existing Strander Boulevard right-of-way minimizes
property acquisition costs but requires a secondary pump station at a capital cost of
$1.5 million. The secondary pump station will also increase O&M costs and life-cycle
costs. Therefore, this route is undesirable.
The second discharge route eliminates the need of a secondary pump station and
conveys water to the west under the UPRR embankment. As discussed above, this route
requires additional easements but the costs are significantly offset by the lack of a
secondary pump station. A gravity system appears to be feasible but survey information
is required to verify that the grades will be acceptable. Assuming the grades are
acceptable, this route would be the preferred discharge route.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 49 of 68
6.0 STORM SYSTEM BUILD ALTERNATIVES
There are a large number of possible alternatives that could be constructed using various
combinations of pump station systems, treatment options, detention options, outfall
location, and discharge route discussed previously. Six possible combinations were
evaluated as described below. The last two, Alternative Nos. 5 and 6, were found to be
not feasible, but are included to illustrate the shortcomings of attempting to acquire
additional right-of-way for the treatment facilities.
6.1 Storm System Build Alternative No. 1
Alternative No. 1 contains the following components.
1. Upgraded pump station (PS-UP) with combined groundwater and stormwater flows
2. Wet biofiltration swale (WQ-SW) for water quality treatment
3. Detention pond with walls (DET)
4. Northern outfall (OUT-N)
5. Discharge route within Strander Boulevard right-of-way (D-SBR), including a
secondary discharge pump station (PS-D)
See Figure 31 for the schematic configuration of this alternative.
This alternative combines the groundwater and stormwater flows downstream of the
two systems. The combined flows are conveyed to the wet well where they enter an
upgraded pump station and are pumped to a higher elevation. See Figure 16 in
Section 5.1.3 for the schematic of the upgraded pump system. Combined flows exit the
meter vault to be routed to a flow splitter-energy dissipator structure. This custom
structure will be designed to dissipate the energy associated with the high-velocity flows
from the pump station and will contain an internal flow splitter. The flow splitter
bypasses the groundwater flow to a wet biofiltration swale where the water will be
treated. The remaining flow will be routed to a detention pond as described in
Section 5.3, Detention Facility.
A control structure in the pond will meter the discharge. Discharge from the pond will
be routed to the wet biofiltration swale. The wet biofiltration swale will treat the pond’s
two-year release rate. Flows above this rate will flow through the swale. All discharge
from the swale will be routed to a flow splitter. A portion of the flow will be routed to
Wetland Q/R to maintain the pre-Phase 2 hydrology as discussed in Section 4.1, Wetland
Hydroperiod Criteria. The remaining flow will be routed to a secondary discharge
pump station (see Figure 29), which will route the water to an energy dissipator then to
the northern outfall. To avoid the cost of the secondary discharge pump station, this
alternative could also use the southern outfall. However, additional easements would be
required.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 50 of 68
With this alternative, the existing pump station capacity will be increased to handle all
combined groundwater and stormwater flows from the Phase 3 area. The rated capacity
will be increased from the existing 3,300 gpm to 6,900 gpm. Modifications to the existing
pump station are as described in Section 5.1.3. The discharge route and associated
pumping system are described in Section 5.5.1.
Figure 31. Schematic Configuration of Alternative No. 1
Key
CS = Control Structure
D-SBR = Discharge Route within Strander Boulevard Right-of-Way
DET = Detention Pond with Walls
FS-ED = Flow Splitter-Energy Dissipator
OUT-N = Northern Outfall
PS-D = Secondary Discharge Pump Station
PS-UP = Upgraded Pump Station
WQ-SW = Wet Biofiltration Swale
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 51 of 68
6.2 Storm System Build Alternative No. 2
This second alternative contains the following components.
1. Upgraded pump station (PS-UP) with combined groundwater and stormwater flows
2. Bioretention pond (WQ-BIO) for water quality treatment
3. Detention Pond with Walls (DET)
4. Southern outfall (OUT-S)
5. Discharge route within easements (D-ESMT)
See Figure 32 for the schematic configuration of the second alternative.
This alternative is similar to Alternative No. 1. Both alternatives use an upgraded pump
station that discharges the combined flows to the flow splitter-energy dissipator and a
detention pond with walls to allow room for a separate water quality facility. For this
alternative, a Bioretention Pond with Underdrain (see Section 5.2.5) replaces the Wet
Biofiltration Swale.
As for Alternative No. 2, a flow splitter-energy dissipator structure is used to route
groundwater to the bioretention pond. Detention pond discharge, via a control
structure, is also routed through the bioretention pond. A control structure in the
bioretention pond will bypass a portion of the flow to Wetland Q/R to maintain the
pre-Phase 2 wetland hydrology.
Unlike the previous alternative, Alternative No. 2 does not require a secondary
discharge pump station because it does not use Strander Boulevard right-of-way. This
alternative will provide a gravity-fed discharge pipe to the southern outfall and could
potentially use the northern outfall. See discussion in Section 5.5.2, Gravity-Fed
Discharge Route within Easements.
With this alternative, the existing pump station capacity will be increased to convey the
stormwater flows from the Phase 3 area. The existing underdrain manhole DR-12 will be
converted to a pump station that will transfer groundwater directly to the new water
quality facility. As stormwater accounts for more than 95 percent of the total Phase 3
combined storm and groundwater design flow, modifications to the existing pump
station required for this alternative are identical to Alternative No. 1. The new
groundwater pump station is described in Section 5.1.3.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 52 of 68
Figure 32. Schematic Configuration of Alternative No. 2
Key
CS = Control Structure
D-ESMT = Discharge Route within Easements
DET = Detention Pond with Walls
FS-ED = Flow Splitter-Energy Dissipator
OUT-S = Southern Outfall
PS-UP = Upgraded Pump Station
WQ-BIO = Bioretention Pond
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 53 of 68
6.3 Storm System Build Alternative No. 3
This third alternative contains the following components.
1. Groundwater pump station (PS-GW) along with an upgraded pump station (PS-UP)
2. Constructed stormwater wetland (WQ-WET) for water quality treatment
3. Detention pond with Walls (DET)
4. Southern outfall (OUT-S)
5. Discharge route within easements (D-ESMT)
See Figure 33 for the schematic configuration of the third alternative.
This alternative is similar to Alternative No. 2, but keeps the stormwater and underdrain
systems separate. The underdrain system routes the groundwater to a groundwater
pump station as discussed in Section 5.1.3. Discharge from the pump station is routed to
an energy dissipator then to a constructed stormwater wetland for water quality
treatment as discussed in Section 5.2.4. Technically, the groundwater does not need to be
treated because it does not contain any roadway pollutants. Routing the groundwater
through the constructed stormwater wetland will aid in the removal of the insoluble
iron prior to gravity flowing to the Green River. If the underpass is sealed, the small
amount of groundwater could be routed directly to the river without being treated. This
eliminates uncertainties inherent in the design of the flow facilities associated with
uncertainties in predicting the amount of groundwater flow.
The stormwater is routed to the upgraded pump station to be discharged to an energy
dissipator prior to entering the detention pond. As with the other alternatives described
above, a control structure will meter the discharge from the pond to the constructed
stormwater wetland where it comingles with the groundwater. A control structure in
the constructed stormwater wetland will route water to Wetland Q/R as discussed
previously.
As with Alternative No. 2, this alternative will provide a gravity-fed discharge pipe to
the southern outfall through easements and could potentially use the northern outfall.
See discussion in Section 5.5.2, Gravity-Fed Discharge Route within Easements.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 54 of 68
Figure 33. Schematic Configuration of Alternative No. 3
Key
CS = Control Structure
D-ESMT = Discharge Route within Easements
DET = Detention Pond with Walls
FS-ED = Flow Splitter-Energy Dissipator
OUT-S = Southern Outfall
PS-GW = Groundwater Pump Station
PS-UP = Upgraded Pump Station
WQ-WET = Constructed Stormwater Wetland
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 55 of 68
6.4 Storm System Build Alternative No. 4
This fourth alternative contains the following components.
1. Upgraded pump station (PS-UP)
2. Constructed combined wetland pond (WQ/DET-WET) water quality treatment and
detention
3. Northern outfall (OUT-N)
4. Discharge route within Strander Boulevard right-of-way (D-SBR), including a
secondary discharge pump station (PS-D) that is similar to the one used in
Alternative No. 1 (see Figure 29 in Section 5.5.1)
See Figure 34 for the schematic configuration of the fourth alternative.
Like Alternative No. 3, the fourth alternative separates the stormwater and underdrain
systems. In this alternative, the groundwater does not get routed through a water
quality treatment system and is directly discharged into the Green River. Stormwater is
routed to constructed combined wetland pond that provides both water quality
treatment and detention. A control structure in the constructed combined wetland pond
will route water to Wetland Q/R in the same manner as discussed in previous
alternatives. The remaining flow will gravity flow to a new secondary discharge pump
station where the treated stormwater will comingle with untreated groundwater in the
secondary discharge pump station to be pumped to an energy dissipator then to the
northern outfall. This alternative could potentially be modified to use the southern
outfall route so that the secondary discharge pump could be eliminated.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 56 of 68
Figure 34. Schematic Configuration of Alternative No. 4
Key
CS = Control Structure
D-SBR = Discharge Route within Strander Boulevard Right-of-Way
FS-ED = Flow Splitter-Energy Dissipator
OUT-N = Northern Outfall
PS-D = Secondary Discharge Pump Station
PS-UP = Upgraded Pump Station
WQ/DET-WET = Constructed Combined Wetland Pond
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 57 of 68
6.5 Storm System Build Alternative No. 5
Alternative No. 5 contains the following components.
1. Upgraded pump station (PS-UP) with combined groundwater and stormwater flows
2. Constructed stormwater wetland (WQ-WET) for water quality treatment
3. Detention Pond (DET – 3H:1V) with 3H:1V side slopes
4. Southern outfall (OUT-S)
5. Discharge route within easements (D-ESMT)
See Figure 36 for the schematic configuration of the fifth alternative.
This alternative is similar to Alternative No. 2, but replaces the detention pond with
walls with a detention pond with 3H:1V side slopes. This pond would occupy the
majority of the available parcel area. This requires the constructed wetland treatment
facility to be constructed “off site,” a parcel of land that is not currently owned by the
City, and would need to be acquired in its entirety. The parcel is not large enough for
the required size of the constructed wetland, so walls would also be required.
Additionally, there would be no room to provide a setback from the property lines or
provide maintenance access.
As for Alternative No. 2, this alternative combines the groundwater and stormwater
flows and pumps them to a higher elevation using an upgraded pump station system.
Pump station modifications for Alternative No. 5 are identical to Alternative No. 2.
Combined flows exit the meter vault to be routed to a FS-ED structure. The flow splitter
bypasses the groundwater flow to the off-site constructed stormwater wetland.
Figure 35. Off-Site Constructed Wetland Section
The remaining stormwater flow will be routed to the detention pond. A control structure
in the pond will meter the discharge. The pond discharge will be routed with the
groundwater flows to the water quality facility. A control structure in the constructed
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 58 of 68
wetland will route water to Wetland Q/R as discussed previously. This will require an
additional pipe under the UPRR embankment and consequently an additional easement.
A gravity-fed discharge pipe from the constructed stormwater wetland will route the
water to the southern outfall.
Figure 36. Schematic Configuration of Alternative No. 5
Key
CS = Control Structure
D-ESMT = Discharge Route within Easements
DET – 3H:1V = Detention Pond with 3H:1V side slopes
FS-ED = Flow Splitter-Energy Dissipator
OUT-S = Southern Outfall
PS-UP = Upgraded Pump Station
WQ-WET = Constructed Stormwater Wetland
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 59 of 68
Alternative No. 5 was determined to be infeasible because the stormwater wetland
cannot be constructed to standards if using setback, maintenance, and access
requirements. Furthermore, this alternative would require an additional discharge pipe
under the UPRR embankment to provide hydrology to Wetland Q/R. Based on initial
calculations, the water quality facility would sit lower than the wetland; therefore, a
pipe to the wetland is also infeasible.
6.6 Storm System Build Alternative No. 6
Alternative No. 6 contains the following components.
1. Upgraded pump station (PS-UP) with combined groundwater and stormwater flows
2. Bioretention pond (WQ-BIO) for water quality treatment
3. Detention pond (DET – 3H:1V) with 3H:1V side slopes
4. Southern outfall (OUT-S)
5. Discharge route within easements (D-ESMT)
See Figure 38 for the schematic configuration of the sixth alternative.
This is essentially identical to Alternative No. 5, but uses a bioretention pond instead of
a constructed stormwater wetland.
In order to fit on the parcel, the water quality facility will need to use walls that will add
to the cost. There would be a bit room for setbacks than with the constructed wetland
pond, these provide limited maintenance access. This alternative would also require an
additional pipe under the UPRR embankment and consequently an additional easement.
A gravity-fed discharge pipe from the constructed stormwater wetland will route the
water to the southern outfall.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 60 of 68
Due to the UPRR utility accommodation policies discussed in Section 5.5.2, the detention
pond discharge pipe to the bioretention pond, the bottom of the facility will be below
the groundwater surface elevation. Because of this, the bioretention pond will not drain
and may become stagnant in the wet season. This in turn will kill all of the bioretention
vegetation and could cause local flooding.
Like Alternative No. 5, this alternative would also require an additional discharge pipe
under the UPRR embankment to provide hydrology to Wetland Q/R. Based on initial
calculations, the water quality facility would sit lower than the wetland; therefore, a
pipe to the wetland is also infeasible.
Figure 37. Off-Site Bioretention Section
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 61 of 68
Figure 38. Schematic Configuration of Alternative No. 6
Key
CS = Control Structure
D-ESMT = Discharge Route within Easements
DET – 3H:1V = Detention Pond with 3H:1V side slopes
FS-ED = Flow Splitter-Energy Dissipator
OUT-S = Southern Outfall
PS-UP = Upgraded Pump Station
WQ-BIO = Bioretention Pond
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 62 of 68
6.7 Pump Station Cost Summary
The component with the highest capital, annual O&M, and life-cycle cost is the pump
station system and the discharge route because it potentially triggers the need for a
secondary pump system. The costs associated with the other components are
comparable and are not included in the evaluation.
The estimated capital cost, annual O&M, and life-cycle costs of the pump station
modification associated with each alternative are summarized in Table 3. The life term
for the lift stations is considered to be 20 years. This is the typical lifespan for major
mechanical and electrical equipment.
The capital costs included above do not include right-of-way, easement, or program
costs.
Table 3. Pump Station Cost Summary
Alternatives Capital Cost Annual O&M Life-Cycle Cost
Alternative 1 $2,450,000 $13,450 $2,719,000
Alternative 2 $650,000 $6,700 $784,000
Alternative 3 $950,000 $9,350 $1,137,000
Alternative 4 $2,450,000 $13,450 $2,719,000
Alternative 5 $650,000 $6,700 $784,000
Alternative 6 $650,000 $6,700 $784,000
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 63 of 68
7.0 CONCLUSIONS AND RECOMMENDATIONS
Based on the results of this preliminary storm system design effort, we offer the
following conclusions and recommendations for the design of Phase 3 of the Strander
grade separation project.
7.1 Need for a Watertight Underpass
The original planning of the project envisioned that Phase 3 of the project would
construct a watertight bottom seal and wall system for the entire length of the existing
Phase 2 project, as well as the Phase 3 extension. The cost of sealing the underpass is
approximately $10 million. This cost is high relative to the reduction in groundwater
design flows achieved. Groundwater inflows for an unsealed underpass are expected to
be between 115 gpm to 295 gpm. Sealing the underpass would reduce these flows to
25 gpm or less. Estimated stormwater flows for Phase 3 are provided in the table below
for comparison.
Table 4. Project Flow Rates
Event Flow Rate
2 years 2,167 gpm
10 years 4,345 gpm
25 years 5,449 gpm
100 years 6,530 gpm
Note: Flow rates estimated using the rational method for the
project site area of 5.47 acres.
Based on the requirements of the latest King County Stormwater Design Manual, the
only acceptable discharge for the anticipated volume of stormwater water would be to
nearby Green River. This would be true even if the project was being constructed
at-grade.
Although the anticipated groundwater flows are small relative to the volume of
stormwater discharge, they are essentially constant throughout the wet season and
continue at a reduced rate in the summer. This creates several risks for the project as
outlined below.
1. If the groundwater is combined with the stormwater and routed through the
detention and treatment facilities, it will be difficult to design the detention and
treatment facilities to function, as required, to mimic natural rainfall patterns and
associated discharges to the adjacent wetlands. The constant flow of water will
essentially be passed through the facility continuously.
2. The exact amount of groundwater inflows will not be known until the facility is
constructed and in operation for a year or more. If the groundwater and
stormwater are combined, flow control features may need to be adjusted or
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Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 64 of 68
reconstructed after the facility is operational to provide the required flows to
detention and treatment facilities, as well as the adjacent wetland.
3. To avoid all of the issues described above, the ground water could be routed
directly to the Green River. However, a plume of iron-tainted water may be
discharged to the Green River on a continual basis. Even with treatment, it is not
known how visible this plume would be. The orange water does not pose a health
but is aesthetically unappealing to the general public who may not understand the
source of the coloration. It is difficult to predict what a detectable volume of
discharge would be and whether this would lead to community concerns and
correcting the issues after construction is completed may be difficult. Minimizing
this discharge would substantially mitigate this risk.
4. The insoluble iron can also coat the walls of pipes and pump systems, causing
long-term maintenance concerns. During construction, the inside pipes of the
dewatering pump system became partially clogged with this material. See Figure 4
in Section 2.0 of this report.
Therefore, based on discussions with the City, it is recommended that the groundwater
be separated from the stormwater and that additional project funding be sought to seal
the underpass and reduce groundwater inflows to an absolute minimum. This will
directly mitigate long-term maintenance risks, as well as potential concerns with the
quality of discharge to the Green River. This will also facilitate separating the
groundwater from the stormwater, which will simplify the design of the detention and
treatment facilities.
If an additional $10 million in funding cannot be secured, the groundwater should be
kept separate from the stormwater and discharged directly to the Green River,
potentially through a separate dedicated treatment facility, such as a filter vault.
Additional study will be required to determine if a plume of discolored water would be
visible.
7.2 Preferred Treatment and Detention Alternative
Assuming the underpass is sealed as recommended above, the preferred treatment and
detention alternative for the project is Alternative No. 4 as shown in Figure 39.
Additional detailed information regarding the components of this proposed stormwater
system is described in Section 5.0 of this report.
Alternative No. 4 separates the groundwater from the stormwater. The detention
facilities are stacked above the water quality facilities, which provides the best use of
space of all of the alternatives. The usage of 3H:1V side slopes provides easier access for
maintenance activities and eliminates the need and cost for walls to contain the
detention pond.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 65 of 68
It is recommended that some modifications to this alternative be considered prior to
completing the final design of the stormwater system. These potential modifications are
outlined below.
1. Consider use of the southern outfall. Currently, this alternative discharges to the
northern outfall, which is not the preferred outfall component.
2. Consider the gravity discharge route. This alternative proposed using the Strander
Boulevard right-of-way, which minimizes easement costs but requires the
secondary discharge pump station that has a higher capital cost and also increases
the long-term maintenance costs. A gravity system appears to be feasible but
survey information is required to verify that the grades will be acceptable.
Assuming the grades are acceptable, this route would be the preferred discharge
route.
As a whole, this alternative provides facilities that have low to moderate maintenance
costs and will be simple to maintain. The capital costs and long-term maintenance costs
of three pump stations may be avoided by pursuing the modifications described above.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 66 of 68
Figure 39. Alternative No. 4 - Preferred Treatment and Detention Alternative
Key
CS = Control Structure
D-SBR = Discharge Route within Strander Boulevard Right-of-Way
ED = Energy Dissipator
OUT-N = Northern Outfall
PS-D = Secondary Discharge Pump Station
PS-UP = Upgraded Pump Station WQ/DET-WET = Constructed Combined Wetland Pond
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 67 of 68
7.3 Opinion of Probable Project Cost
An updated project cost estimate was prepared and a summary is attached in
Appendix F. The estimate includes a brief narrative describing the basic assumptions
used to prepare the estimate. The total project cost is anticipated to be $54.5 million.
7.4 Recommendations for Future Work
There are several steps that should be taken to confirm some of the assumptions used in
this preliminary design effort prior to starting the plan, specification, and cost estimate
(PS&E) effort. Each of these are described below.
7.4.1 Outreach to Property Owners regarding Required Easements
It is recommended that the City contact property owners from whom easement may be
required to allow the proposed discharge to be routed to the south outfall. The project’s
design features benefit from the use of this route. These are obviously alternatives, but if
the City determines it would be best to avoid these easements, the design should be
based on a discharge route located within the existing Strander Boulevard right-of-way.
7.4.2 Confirm Use of Temporary Tiebacks for Walls
The proposed wall design uses sheet pile with temporary tiebacks during construction.
The tiebacks will extend beyond City right-of-way. Temporary easements will be
required for construction of the tiebacks. The ability to acquire these easements and
coordination with potential utility conflicts needs to be investigated in greater detail.
The temporary tiebacks may be required to be removed after they are no longer needed.
7.4.3 Confirm South Outfall Location
Topography survey of the existing outfall should be obtained so the grades of the
proposed gravity discharge can be confirmed.
7.4.4 Model Wetland Q/R Inundation
Approximate methods have been used to quickly size and evaluate the alternative
presented in this study. The preferred stormwater system should be modeled in detail,
early in the final design phase of the project and based on the final geometrics if they
differ significantly from the preliminary design. A detailed simulation of the proposed
method for restoring the hydroperiod for Wetland Q/R should be completed to confirm
the project can conform to the latest Ecology requirements.
7.4.5 Update Groundwater Model
If the underpass is sealed, further work on the groundwater model is likely not to be
required. However, if the underpass is not sealed, the groundwater model should be
updated to incorporate the project’s finalize design geometrics. In addition, another
year’s worth of pumping data will be available, including the winter of 2016/2017. If the
underpass is not sealed, the groundwater model calibration should be revisited using
these winter pumping rates because the data obtained during the 2015/2016 was
corrupted and not suable.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 68 of 68
7.4.6 Obtain Flow Metering Data Upstream of Existing Pump Station
An upgrade to the existing pump station may be avoided if flow metering data can be
obtained upstream of the pump station. Metering of both the stormwater and
groundwater is needed upstream of where they are combined. This data could provide a
basis for establishing a lower design flow than that obtained by the rational method.
Final Draft Submittal BergerABAM, A16.0187.00
Stormwater System Conceptual Design Report 7 April 2017
Strander Grade Separation Phase 3 Page 69 of 68
8.0 LIST OF ACRONYMS AND ABBREVIATIONS
BMP best management practice
CSM conceptual site model
Ecology Washington State Department of Ecology
FS-ED flow splitter-energy dissipator
gpm gallon per minute
hp horsepower
HRM Highway Runoff Manual
KCSWDM King County Surface Water Design Manual
kW kilowatt
LID low impact development
MCC motor control center
NEPA National Environmental Policy Act
O&M operation and maintenance
PLC programmable logic controller
PS&E plan, specification, and cost estimate
Pu Puget Silty Clay Loam
PVC polyvinyl chloride
Py Puyallup Fine Sandy Loam
SCADA Supervisory Control and Data Acquisition
SR 181 State Route 181
SMMWW Stormwater Management Manual of Western Washington
UGA Urban Growth Area
UPRR Union Pacific Railroad
Wo Woodinville Silt Loam
WSDOT Washington State Department of Transportation
WTM Wetland Technical Memorandum
DRAFT Hydrogeologic Study for the Strander Boulevard ExtensionPhase 3 – Preliminary Design
City of Tukwila, Washington
December 6, 2016
Submitted To:
BergerABAM
33301 Ninth Avenue South, Suite 300
Federal Way, Washington 98003-2600
By:
Shannon & Wilson, Inc.
400 N 34th Street, Suite 100
Seattle, Washington 98103
21-1-22205-001
21-1-22205-001_R1/wp/lmr 21-1-22205-001 i
TABLE OF CONTENTS
Page
1.0 INTRODUCTION ..................................................................................................................1
1.1 Scope of Services .......................................................................................................1
1.2 Site Description ..........................................................................................................1
1.3 Previous Project Phases ..............................................................................................1 1.4 Phase 3 Project Description ........................................................................................2
2.0 GENERAL GEOLOGIC CONDITIONS ..............................................................................2
3.0 GEOTECHNICAL AND HYDROGEOLOGIC EXPLORATIONS ....................................3
3.1 Subsurface Explorations .............................................................................................3
3.2 Slug Testing ................................................................................................................3 3.3 Laboratory Testing .....................................................................................................4 3.4 Soil Hydraulic Conductivity using Grain Size Data ..................................................4
3.5 Groundwater Levels ...................................................................................................5
3.6 Pond Monitoring ........................................................................................................5
3.7 Hydrostratigraphy and Groundwater Flow ................................................................6
4.0 GROUNDWATER FLOW MODELING ..............................................................................6 4.1 Overview ....................................................................................................................6
4.2 Model Development and Calibration .........................................................................7
4.2.1 Conceptual Site Model (CSM).....................................................................7
4.2.2 Model Domain and Structure .......................................................................8 4.2.3 Model Calibration ........................................................................................8 4.3 Model Simulations .....................................................................................................9
4.4 Flow Mitigation Options ..........................................................................................10
5.0 SUMMARY AND CONCLUSIONS ...................................................................................11
6.0 LIMITATIONS ....................................................................................................................12
7.0 REFERENCES .....................................................................................................................14
TABLES 1 Soil Boring and Well/VWP Completion Details
2 Water Budget for Stormwater Pond - Phase 3 Base Case
3 Estimated Water Budget for Phase 3 Mitigation Cases
TABLE OF CONTENTS (cont.)
21-1-22205-001_R1/wp/lmr 21-1-22205-001 ii
FIGURES
1 Vicinity Map
2 Project Phases
3 Previous and Phase 3 Exploration Plan 4 Groundwater Level and Green River Stage Data
5 Stormwater Pond Levels and Local Precipitation Data
6 Subsurface Profile A-A’
7 Conceptual Water Budget for Phase 2 System
8 Groundwater Model Domain, Boundary Conditions and Layering 9 Phase 3 Model Computational Mesh, Drain Areas and Pond
10 Model-estimated Groundwater Inflow to Phase 3 Underdrain System
11 Model-estimated Overflow from Phase 3 Stormwater Pond
APPENDICES
A Field Exploration and Hydrogeologic Data
B Laboratory Data Report
C Groundwater Flow Modeling D Important Information About Your Geotechnical/Environmental Report
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HYDROGEOLOGIC STUDY FOR THE STRANDER BOULEVARD EXTENSION
PHASE 3 - PRELIMINARY DESIGN
CITY OF TUKWILA, WASHINGTON
1.0 INTRODUCTION
1.1 Scope of Services
This report presents Shannon & Wilson, Inc.’s (S&W’s) hydrogeologic evaluation of the
proposed Phase 3 for the Strander Boulevard Project located in Tukwila, Washington (Figure 1).
Phase 3 extends Strander Boulevard to the west, beneath the Union Pacific Railroad (UPRR)
tracks. Our scope of services included:
Performing geotechnical explorations and laboratory testing;
Installing groundwater observation equipment;
Installing surface water observation equipment;
Developing a groundwater flow model for the Phase 3 project area to predict
groundwater inflows and stormwater pond recharge; and
Evaluating options to reduce overflow from the pond.
We performed our scope of services in accordance with our consultant agreement as authorized
by BergerABAM.
1.2 Site Description
The project site is located in a north-south trending alluvial valley near the south end of Lake
Washington, located south of Interstate I-405 and bounded by West Valley Highway and East
Valley Road (Figure 2). The Green River is about 500 feet west of the westernmost end of the
proposed alignment (the intersection of Strander Boulevard and West Valley Highway). The
Green River meanders but generally flows south to north. Springbrook Creek is located east of
the project site and also flows from south to north.
1.3 Previous Project Phases
Figure 2 shows the location of Phase 2 of the project, which was completed in 2014. Phase 2
included constructing an underpass beneath the BNSF Railway (BNSF) railroad tracks. The
bottom of the underpass is at about elevation 10 feet, which is about 9 feet below the
groundwater table. The underpass side slopes were designed to accommodate groundwater
seepage, and an underdrain system was installed beneath the underpass. Water collected in the
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underdrain system is comingled with stormwater runoff collected from a separate drain system
and is pumped to a nearby stormwater pond. Since 2014, the stormwater pond has been
regularly overflowing into an adjacent wetland. However, the overflow rate has not been
formally measured.
During Phase 2 construction, BergerABAM personnel observed that the excavation for the
BNSF bridge foundation extended into relatively permeable alluvial soil. The excavation was
backfilled with either gravel borrow or a mixture of gravel borrow and the estuarine/overbank
deposits. S&W (2014) evaluated the impacts on the underdrain system from this excavation.
1.4 Phase 3 Project Description
Phase 3 will complete two lanes of the eventual four-lane facility and will continue to use the
permanent groundwater collector system installed for Phase 2 (Figure 2). Some modifications to
the pump station and water collection system are expected to be required. Groundwater will be
separated from the stormwater and a new groundwater pumping system will be used to pump
groundwater to an outfall in the Green River. The discharge location has yet to be identified.
The key issues for the design of development of Phase 3 are to estimate: (1) the groundwater
inflow into the planned Phase 3 permanent groundwater underdrain system and (2) the overflow
from what will be an expanded stormwater pond, located south of Strander Boulevard (Figure 3).
2.0 GENERAL GEOLOGIC CONDITIONS
The project site is located in a relatively flat alluvial valley that contains the Green, Black,
Duwamish, and Cedar Rivers. The site geology is characterized by the following
hydrostrigraphic units:
Holocene Fill (fill) – Hf
Holocene Estuarine/Overbank Deposits – He and Ha(o)
Holocene Peat (peat) – Hp
Holocene Alluvium – Ha
Vashon glacial outwash - Qva
The Holocene fill is human-placed fill soil of varying thickness, and consists of soils that
encompass a range of soil types and hydraulic properties. The Hf unit is found near the ground
surface, approximately elevation 25 feet.
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The He unit consists of fine-grained floodplain and deltaic soils deposited by the Duwamish and
Cedar Rivers. The soils consists of very soft to medium stiff, slightly fine sandy, clayey silt to
silty clay with scattered organics and discrete peat lenses and layers. This unit has relatively low
permeability and these soils are generally located between ground surface and elevation -5 feet.
They are interbedded with peat and sands, with deeper estuary/overbank soils found in the west
side of the alignment between approximately elevations -50 and -75 feet. The peat (Hp) forms
layers of organic, fine-grained soils located between approximately elevations 10 and 0 feet.
Peat layers are generally between 1 and 3 feet thick, interbedded in the He unit deposits, and
have relatively low permeability.
The Ha unit generally consists of fine- to medium-grained alluvium deposited in the channels of
the Green/Duwamish River, and is not glacially overridden. Its range of hydraulic conductivity
is low to high, depending on the fines content of the soil. A discontinuous fine-grained (silty
clay to silty fine sand) interbedded estuary/overbank unit exists between elevations -50 and -75
feet in the western part of the alignment. A lower Ha unit (consisting of clean to slightly silty,
fine to medium sand) exists beneath the interbedded unit. A regional Vashon outwash aquifer
has was previously identified in the Phase 2 soil boring B-103 at a depth of 172.5 feet (elevation
-140 feet). However, this unit has a relatively insignificant influence on the hydrogeologic
behavior of the project elements.
3.0 GEOTECHNICAL AND HYDROGEOLOGIC EXPLORATIONS
3.1 Subsurface Explorations
The Phase 3 subsurface exploration program consisted of three soil borings and five cone
penetration tests (CPTs). Figure 3 shows the exploration locations. Borings B-1 and B-2 were
drilled to 101.5 feet below ground surface (bgs) and B-3 was drilled to 141.5 feet bgs. The CPTs
were advanced to depths of 80 feet bgs. Table 1 summarizes the three soil boring details and the
groundwater observation well and vibrating wireline piezometer (VWP) completion details.
Appendix A includes the boring logs, well construction details, and CPT report.
3.2 Slug Testing
We performed slug tests at monitoring wells B-1-ow, B-2-ow, and B-3-ow. Slug testing is a
method for estimating the in situ horizontal hydraulic conductivity (Kh) of the saturated material
surrounding the screened zone of a monitoring well. The results indicate the upper Ha unit Kh
ranges from 9 to 48 feet/day (3.3 x 10-3 to 1.7 x 10-2 centimeters/second [cm/sec]). This range is
21-1-22205-001_R1/wp/lmr 21-1-22205-001 4
typical for silty sand and poorly graded sand. Appendix A presents additional details concerning
the test method, data interpretation, and results.
3.3 Laboratory Testing
We performed the following tests on selected soil samples:
Visual classification – using a system based on ASTM International (ASTM) D2487-
11, Standard Practice for Classification of Soils for Engineering Purposes (ASTM,
2011).
Water Content - in accordance with ASTM D2216-10, Standard Test Methods for
Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass (ASTM, 2010a).
Sieve analysis – in accordance with ASTM C136-14, Standard Test Method for Sieve
Analysis of Fine and Coarse Aggregates (ASTM, 2014a), and ASTM D1140-14,
Standard Test Methods for Determining the Amount of Material in Soils Finer than
0.075 millimeter (no. 200) Sieve in Soils by Washing (ASTM, 2014b).
Specific gravity – in accordance with ASTM D854-14, Standard Test Methods for
Specific Gravity of Soil Solids by Water Pycnometer (ASTM, 2014c).
Particle-size analysis - in accordance with ASTM D422-63(2007)e2, Standard Test
Method for Particle Size Analysis of Soils (ASTM, 2007).
Atterburg Limits - in accordance with ASTM D4318-10e1, Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils (ASTM, 2010b).
Appendix B presents the results of the tests.
3.4 Soil Hydraulic Conductivity using Grain Size Data
We used the laboratory results from the grain size analysis data to estimate the hydraulic
conductivity (K) for 17 samples using four empirical methods (see Odong, 2007). The following
summarizes the results for each hydrogeologic unit:
He and Ha(o) unit: K = 10-3 to 0.4 feet/day; geometric mean = 0.04 feet/day (1.5 x
10-5 cm/sec)
Upper Ha unit: K = 22 to 66 feet/day; geometric mean = 35 feet/day (1.2 x 10-2
cm/sec)
Lower Ha unit: K = 2 x 10-3 to 4 x 10-3 feet/day; geometric mean = 3 x 10-3 feet/day (1
x 10-6 cm/sec)
21-1-22205-001_R1/wp/lmr 21-1-22205-001 5
The results for the six samples from the He and Ha(o) units (mostly silt and clay) had the largest
range and a relatively low average K (0.04 feet/day). The upper Ha unit results are relatively
uniform and the average K is within the range obtained for the slug tests in the three monitoring
wells (9 to 48 feet/day). The two lower Ha unit samples (both described as silt) had a relatively
low K. These results indicate that the lower Ha unit likely acts locally as a lower confining unit
for the upper Ha unit.
3.5 Groundwater Levels
Figure 4 shows the hydrographs for the observation wells and VWPs, and daily precipitation (at
the nearby Renton Airport climate station) until November 4, 2016. Appendix A describes the
data logging equipment.
The highest groundwater elevations were recorded in shallow B-2-vwp. Measured groundwater
levels ranged from elevation 21.5 feet (in April 2016) to below elevation 17 feet when the probe
became dry.
In the three monitoring wells completed in the upper Ha unit, groundwater levels ranged from a
high of 13 feet (in April 2016) to 9 feet (in September 2016). The groundwater elevation in well
B-3-ow (closest to the Phase 2 underdrain system) was consistently the lowest, whereas the
groundwater elevation in well B-1-ow (closest to the Green River) was the highest.
In the deeper B-3-vwp, the groundwater elevations ranged between elevations 12.5 feet and 9.25
feet. The levels were slightly higher than in the three upper Ha unit wells in the summer but
lower in the spring and fall.
3.6 Pond Monitoring
As described in Appendix A, we installed a pressure transducer and data logger at the southern
end of the stormwater pond adjacent to the overflow structure, and another in the wetland to the
south of the pond berm (Figure 2). Figure 5 shows the surface water level hydrographs and the
daily precipitation amounts for the Renton Airport station. As neither instruments were surveyed
for elevation, the elevations presented here are approximate. The surface water levels generally
declined during the summer, and the wetland probe became dry in early July 2016. Heavy rain
during October 2016 resulted in the pond level rising by up to 0.5 feet and the probe in the
wetland becoming wet again.
21-1-22205-001_R1/wp/lmr 21-1-22205-001 6
3.7 Hydrostratigraphy and Groundwater Flow
Figure 6 shows the interpreted subsurface soil conditions and hydrostratigraphy along a section
west to east though the planned Phase 3 and existing Phase 2 area. The section includes soil
information from the current and previous borings and explorations, and the Phase 2 constructed
roadway profile.
The upper 30 feet consists of generally low permeable silt and clay which form the He unit. At
borings B-1, B-2, and B-101, the upper 10 feet contains organic sand, which we classified as the
Ha(o) unit. The shallowest recorded groundwater is at approximately 8 feet bgs (elevation 20
feet) in B-1-vwp.
The underlying upper Ha unit consists of poorly graded sand and is between 25 and 50 feet thick
beneath the planned Phase 3 expansion. This unit is thinnest at the western part of the expansion
(based on boring B-1). In November 2016, the groundwater levels in the three Phase 3
monitoring wells were at approximately elevation 12 feet. Therefore, the piezometric level in the
upper Ha unit was between 8 and 10 feet lower than in the overlying He/Ha(o) water table unit.
Based on the results of S&W (2014), the Ha unit is likely hydraulically connected to the Phase 2
underdrain system because of the excavation that occurred during construction.
A variably-thick silt unit underlies and acts as a lower confining unit in parts for the upper Ha
unit. Where present, this silt unit is up to 30 feet thick and overlies a lower, coarse sand Ha unit.
This silt unit appears to be absent beneath and to the east of the BNSF right-of-way.
A lower Ha unit was encountered in several of the deeper borings at a depth of 115 feet bgs
(elevation -85 feet). Based on data from B-3-vwp, the groundwater elevation in this unit was
similar or slightly higher than in the upper Ha unit indicating that there is an upward hydraulic
gradient across the confining silt unit. This is likely due to the effect of the Phase 2 underdrain
system that is lowering the groundwater level in the upper Ha unit but has little to no effect on
groundwater in the lower Ha unit.
4.0 GROUNDWATER FLOW MODELING
4.1 Overview
We developed a three-dimensional groundwater flow model (the model) to estimate groundwater
inflows to the planned Phase 3 underdrain system and the infiltration potential for the expanded
Phase 3 stormwater pond. The modeling involved the following steps:
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Developing a conceptual site model (CSM) for the project site and surrounding area.
Building the model using the United States Geological Survey’s code MODFLOW-USG (Panday and others, 2015) and the graphical-user interface program GMS version 10 (Aquaveo, 2016) based on the CSM;
Calibrating the model to reasonably reproduce historic data (recorded groundwater
levels and pumping station flows); and
Simulating the planned Phase 3 underdrain system and stormwater pond to predict groundwater inflow and infiltration rates under three hydrologic conditions.
We also evaluated a series of discharge mitigation options to reduce the volume of water to be
disposed.
4.2 Model Development and Calibration
4.2.1 Conceptual Site Model (CSM)
The CSM was based on proposed Phase 3 project details, and incorporated quantitative
components of local hydrology (surface water levels and precipitation-derived recharge) and
hydrogeology (aquifer/aquitard properties, groundwater levels and gradient, discharge at the
Phase 2 underdrain system). Appendix C presents the hydrology and hydrogeology data.
Figure 7 shows the conceptual hydrogeologic and groundwater flow budget components
for the existing subsurface underdrain and stormwater system. The key inflow and outflow
components are:
1. Groundwater enters the underdrain system and surface runoff (from
precipitation events) enters the stormwater drain system.
2. The combined groundwater and runoff drain system inflow is pumped to the stormwater pond, assuming no losses.
3. In the pond, water infiltrates the relatively low permeable surficial soils,
evaporates, or overflows the pond weir to the wetlands (when the infiltration
and evaporative capacities are exceeded.)
Therefore, for the purpose of this analysis:
Pond Overflow = Combined Drain Inflow – Infiltration – Evaporation
21-1-22205-001_R1/wp/lmr 21-1-22205-001 8
4.2.2 Model Domain and Structure
The model occupies an area 2,750 feet by 2,000 feet (Figure 8). The model uses the
MODFLOW Constant Head transient boundary type to represent the Green River to the west and
the Springbrook creek and wetland to the east. The northern and southern boundaries are No-
flow type. The model uses eight discrete layers to represent the upper 100 feet of unconsolidated
sediments; the model’s upper surface coincides with land surface, and the bottom of the model is
at elevation -75 feet. In general, layers 1 through 4 simulate the He and Ha(o) units, and layers 5
through 8 simulate the upper Ha unit (Figure 8).
The model uses the MODFLOW Drain condition to simulate the underdrain system and
the MODFLOW General Head condition to represent the stormwater pond. Although both of
these boundary condition functions allow groundwater to leave the model, only the General
Head allows surface water to also recharge the aquifer. Therefore, although the model can
explicitly calculate the groundwater inflow into the underdrains and the infiltration at the pond,
the surface runoff and evaporation components of the water budget are calculated separately.
The model includes a discrete high permeable area in layers 3 and 4 that represents the
“window” that was excavated through the He unit through to the underlying upper Ha unit
during the construction of the Phase 2 system (see Figure 6, and Figure C-11 in Appendix C).
This window is believed to be a significant conduit for deeper groundwater to enter the existing
underdrains.
4.2.3 Model Calibration
We calibrated the model to the following data sets:
The 24-hour constant rate pumping test performed for Phase 2 using well PW-
1 in 2010 (S&W, 2011), and
The historical groundwater level and Phase 2 underdrain system discharge data for the 21 month period from February 2015 through October 2016.
The calibration results are presented in Appendix C. Overall, the model adequately
reproduced the observed pumping and discharge data. However, data from the existing pump
station for the wettest portion of the February 2015 through October 2016 period was corrupted
and not useable for the calibration effort. Additional calibration efforts using groundwater level
and underdrain inflow data from the 2016-2017 winter season will be used to improve the
confidence in the model.
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4.3 Model Simulations
We used the calibrated model to simulate the expanded Phase 3 underdrain and stormwater pond
system. For the purpose of this analysis, we term this the Base Case. We ran the Base Case for
three hydrologic conditions, each run at steady-state. These conditions are:
Average annual hydrology – typical average precipitation-derived recharge (equal
to 6 inches per year, which is 16 percent of total annual precipitation); mid-year
Green River stage (elevation 14 feet); and eastern boundary groundwater level
(elevation 16 feet).
Normal winter season – typical winter Green River stage (elevation 20 feet) and eastern boundary groundwater level (elevation 18 feet).
Wet winter season – high winter Green River stage (elevation 23 feet) and eastern
boundary groundwater level (elevation 20 feet).
We revised the calibrated model’s computational mesh to include a denser grid in the area of the
planned Phase 3 drains and enlarged stormwater pond (Figure 9). The smallest cells have plan
view dimensions of 5 feet by 5 feet.
Table 2 summarizes the estimated water budget for the Phase 3 underdrain and stormwater pond
system for the three hydrologic conditions for the Base Case. The total inflow to the Phase 3
drain system is equal to the groundwater inflow (calculated by the model) and estimates for
surface runoff for an average annual precipitation of 36 inches (equal to 10 gpm on average and
60 gpm in the wet season). The model estimates that:
The groundwater inflow to the Phase 3 underdrain system would be approximately 150
gpm for average annual conditions and approximately 355 gpm for the wet winter
condition.
Assuming that the total inflow to the pump station is conveyed to the stormwater pond,
the overflow from the pond to the wetlands could be on the order of 130 gpm (average
annual condition) and 405 gpm (wet winter condition).
These overflow rates are between 10 and 50 percent higher than those estimated by the
model for the existing Phase 2 underdrain system under the same hydrologic conditions
(120 gpm and 270 gpm, respectively).
21-1-22205-001_R1/wp/lmr 21-1-22205-001 10
4.4 Flow Mitigation Options
We used the model to evaluate the potential to reduce the groundwater inflows to the Phase 3
underdrain system and/or limit overflows from the stormwater pond. We developed the
following four concepts:
Case A – reduce the permeability of the over excavated window through the He unit
in the Phase 2 excavation by grouting.
Case B – install low permeability cut-off walls through the He unit and partially
through the upper Ha unit.
Case C – re-inject water collected at the pump station in recharge wells located around the stormwater pond perimeter.
Case D – combined Cases A and C.
Case A assumed that the permeability of the over-excavated window through the base of the He
unit could be reduced by grouting. In practice, this would likely involve removal of some of the
existing structures. We simulated this option by decreasing the hydraulic conductivity of the
material in model layers 3 and 4 (the lower half of the He unit) from 250 ft/day to 0.5 ft/day.
This case was run for the three hydrologic conditions.
Case B involved installing impermeable sheet walls around the northern, eastern, and southern
ends of the Phase 2 underdrains where the over-excavation took place. The goal of this action
was to reduce inflow from the upper Ha unit. We simulated three wall depths, one each
extending from ground surface to elevations -5 feet, -25 feet, and -50 feet. We ran these three
cases only for the average hydrologic condition.
Case C involved simulating six shallow groundwater wells that re-inject water removed at the
pump station as a means to reduce (or eliminate) the overflow from the pond. The wells were
simulated to recharge to the middle part of the upper Ha unit (model layers 6 and 7). The
analysis consisted of an iterative process during which the number of wells and their assigned
recharge rates were balanced to roughly equal the model-estimated inflow to the pumping station
minus losses from evaporation and pond infiltration. This case was run for the three hydrologic
conditions.
Table 3 summarizes the estimated water budget results for these mitigation cases. Figure 10
shows the estimated groundwater inflow to the existing (Phase 2) and new (for the Phase 3
system) underdrains for the Base Case and four mitigation option cases. Figure 11 shows the
estimated total groundwater inflow to the Phase 3 underdrain system and the estimated net
21-1-22205-001_R1/wp/lmr 21-1-22205-001 11
overflow from the stormwater pond to the wetlands for each case. The results indicate the
following:
For Case A, grouting the window through the relatively low permeability He unit, the
groundwater inflow to the Phase 3 underdrains and the pond overflow would be
between 50 gpm (average) and 115 gpm (wet winter). The estimated pond overflow rates are 35 gpm and 165 gpm, which are 25 and 40 percent of those estimated for the
Base Case.
For Case B, the cut-off wall options would have negligible effects on groundwater
inflows to the Phase 3 system. This option would only be beneficial if the wall could
be keyed into a low permeability soil unit to reduce vertical flow from the lower part of the Ha unit.
For Case C, the six recharge well option could theoretically greatly reduce the
overflow from the stormwater pond (despite increasing the groundwater inflow to the
pumping system by between 10 and 20 percent). However, there would be significant
practical challenges in operating and maintaining these wells.
The hybrid Case D would reduce the required recharge rate for each well from 165
gpm (for Case C) to 55 gpm for the average hydrology condition. This would make
this option more practically feasible.
To evaluate model sensitivity, we simulated the wet winter hydrologic condition for the Base
Case using a revised version of the calibrated model that included higher He and Ha unit
permeabilities, and higher underdrain conductance values (see the sensitivity analysis presented
in Appendix C). The results indicated that the groundwater inflow to the Phase 3 underdrain
system would be approximately 500 gpm, which is 40 percent higher than for the 355 gpm
estimated for the Base Case.
5.0 SUMMARY AND CONCLUSIONS
S&W performed subsurface explorations and installed groundwater observation equipment to
evaluate the subsurface conditions and provide permanent dewatering and stormwater pond
design recommendations for the planned Phase 3 expansion at the Strander Boulevard project in
the City of Tukwila, Washington. The field explorations identified soil conditions that are
generally similar to those encountered during earlier phases of the project, consisting of a 30 foot
thick unit of relatively low permeable silt, clay and organic overbank soils (the He unit)
overlying at least 30 feet of poorly graded alluvial sand (the Ha unit). The upper unit contains
shallow, perched groundwater less than 10 feet below grade, and the groundwater in the alluvium
is typically 15 to 20 feet below grade. Temporal changes in groundwater are influenced by the
nearby Green River.
21-1-22205-001_R1/wp/lmr 21-1-22205-001 12
We developed a groundwater flow model of the project area, and calibrated the model to
adequately reproduce groundwater levels observed during the 2010 pumping test, and
groundwater levels and Phase 2 subsurface drain inflows for the period February 2015 through
October 2016. We used the model to simulate the planned Phase 3 underdrain expansion to
estimate groundwater inflows and potential infiltration capacity for an enlarged stormwater pond
(termed the Base Case). The model estimated average annual and wet winter groundwater
inflow in the order of 150 gpm and 355 gpm, respectively. Adding surface runoff flows, the
estimated total inflow to the Phase 3 pump station would be 160 gpm (average annual) and 415
gpm (wet winter). The resulting stormwater pond overflow rates would be on the order of 130
gpm (average annual) and 405 gpm (wet winter).
We also used the model to evaluate four groundwater inflow and disposal mitigation options;
these consisted of removing the Phase 2 over-excavated window through the He unit (Case A),
installing impermeable cut-off walls around three sides of this window (Case B), installing and
operating a series of recharge wells to re-inject extracted groundwater to the Ha aquifer (Case C),
and a combination of the window removal and recharge well options (Case D). The analysis
indicated that:
Case A would reduce the groundwater inflow to 50 gpm (average) and 165 gpm (wet
winter); these rate are less than 35 percent of the inflow estimated for the Base Case. However, the implementation of this option would likely involve removal of some of the existing structures.
The cut-off wall option for Case B would have minimal impact to the groundwater
inflow into the underdrains owing to the lack of a low permeable unit that would
reduce upward flow from the lower part of the Ha unit.
Case C would eliminate overflow from the stormwater pond by re-injecting the drain
system inflow. However, operation and maintenance of recharge wells would be a
long-term, costly undertaking.
We recommend that the City of Tukwila continue to monitor groundwater and pond stage levels,
and update the hydrographs through the winter and spring of 2016-2017.
6.0 LIMITATIONS
The analyses, conclusions, and recommendations contained in this report are based on site
conditions as they presently exist. We further assume that the current field explorations are
representative of the subsurface conditions at the proposed project alignment; that is, the
subsurface conditions everywhere in the vicinity of the project are not significantly different
21-1-22205-001_R1/wp/lmr 21-1-22205-001 13
from those disclosed by the field explorations. Within the limitations of the scope, schedule, and
budget, the analyses, and conclusions presented in this report were prepared in accordance with
generally accepted professional geotechnical engineering and hydrogeologic principles and
practice in this area at the time this report was prepared. We make no other warranty, either
express or implied. These results and conclusions were based on our understanding of the
project as described in this report and the site conditions as interpreted from the field
explorations.
Unanticipated soil conditions are commonly encountered and cannot be fully determined by
merely taking soil samples or completing test explorations. Such unexpected conditions
frequently require that additional expenditures be made to attain a properly constructed project.
Therefore, a contingency fund is recommended to accommodate such potential extra costs.
This report was prepared for the exclusive use of BergerABAM. It should be made available to
prospective contractors for information on factual data only, and not as a warranty of subsurface
conditions such as those interpreted from the exploration logs and presented in the discussions of
subsurface conditions included in this report.
Shannon & Wilson has prepared Appendix D, "Important Information About Your
Geotechnical/Environmental Report," to help you understand the use and limitations of our
report. The scope of our services did not include an environmental assessment or evaluation
regarding the presence or absence of wetlands or hazardous or toxic materials in the soil, surface
water, groundwater, or air, on or below or around the site. Shannon & Wilson has qualified
personnel to assist you with these services should they be necessary. We appreciate the
opportunity to be of service to you.
SHANNON & WILSON, INC.
DRAFT DRAFT
Stephen D. Thomas, L.HG. Jeremy N. Butkovich, PE
Associate, Hydrogeologist Project Manager, Senior Engineer
SDT:JNB/sdt
21-1-22205-001_R1/wp/lmr 21-1-22205-001 14
7.0 REFERENCES
Aquaveo, LLC, 2014, Groundwater modeling software GMS (v. 10.1): Provo, Utah, Aquaveo, LLC.
Odong, Justine, 2007, Evaluation of empirical formulae for determination of hydraulic
conductivity based on grain-size analysis: The Journal of American Science, v. 3, no. 3, p.
54-60, available: http://www.jofamericanscience.org/journals/am-sci/0303/.
Panday, Sorab; Langevin, C. D.; Niswonger, R. G.; and others, 2013, MODFLOW-USG version 1: An unstructured grid version of MODFLOW for simulating groundwater flow and tightly
coupled processes using a control volume finite-difference formulation: U.S. Geological
Survey Techniques and Methods 6-A45, 68 p/., available:
https://pubs.er.usgs.gov/publication/tm6A45.
Shannon & Wilson, Inc., 2004, Geotechnical report for conceptual design, Strander Boulevard/SW 27th Street improvements, Renton and Tukwila, Washington: Report
prepared by Shannon & Wilson, Inc., Seattle, Wash., 21-1-09369-002, for Perteet
Engineering, Inc., Everett, Wash., February.
Shannon & Wilson, Inc., 2010a, Draft geotechnical report, Strander Boulevard underpass phase I, Renton/Tukwila, Washington: Report prepared by Shannon & Wilson, Inc., Seattle, Wash., 21-1-21292-001, for Berger/ABAM, Federal Way, Wash., April.
Shannon & Wilson, Inc., 2010b, Draft groundwater dewatering memorandum, Strander
Boulevard underpass phase I, Renton, Washington – BergerABAM project no. FAPWT-09-
175: Memorandum prepared by Shannon & Wilson, Inc., Seattle, Wash., 21-1-21292-001, for Berger/ABAM, Federal Way, Wash., May.
Shannon & Wilson, Inc., 2011, Strander Boulevard underpass phase II, revised dewatering
evaluation: Report prepared by Shannon & Wilson, Inc., Seattle, Wash., 21-1-21292-003,
for Berger/ABAM, Federal Way, Wash., May.
Shannon & Wilson, Inc., 2014, Strander Boulevard underpass phase II, revised groundwater inflow rates for Strander Boulevard Extension underdrains: Report prepared by Shannon &
Wilson, Inc., Seattle, Wash., 21-1-21292-014, for Berger/ABAM, Federal Way, Wash., May
8.
TABLE 1
SOIL BORING AND WELL/VWP COMPLETION DETAILS
SHANNON & WILSON, INC.
Ground
Surface
Elevation1 Boring Drilled
Depth
feet feet
B-1 B-1-ow 28.0 101.5 -17.0 to -27.0 Upper Ha
B-2-vwp He/Ha(o)
B-2-ow -8.0 to -18.0 Upper Ha
B-3-ow -17.5 to -27.5 Upper Ha
B-3-vwp Lower Ha
Notes:
1 - estimated as not surveyed
ow - observation well (2-inch-diameter casing/screen)
vwp - vibrating wireline piezoemeter
He/Ha(o) - Holocene estuarine/overbank unit
Ha - Holocene alluvium unit
Hydrogeologic Unit
B-2
B-3 27.5
Exploration
27.0
141.5
101.5
feet
Well Screen/VWP
Elevation
17.0
-92.0
21-1-22205-001_T1 DRAFT 21-1-22205-001
TABLE 2
WATER BUDGET FOR STORMWATER POND - PHASE 3 BASE CASE
SHANNON & WILSON, INC.
Average annual 160 (150 + 10) 5 25 130
Normal winter 285 (255 + 30) 0 15 270
Wet winter 415 (355 + 60) 0 10 405
Notes:
Units are gpm.
GW = groundwater
Runoff estimated using the Rational Method and precipitation data for Feb. 2016 - Oct. 2016 (provided by BergerABAM, Nov. 3, 2016)
Hydrologic Case
Phase 3 System
(GW + Runoff)
{A}
Evaporation Loss at
Pond
{B}
Infiltration at Pond
{C}
Estimate Overflow
from Pond
{D = A-B-C}
21-1-22205-001_T2/wp/lmr DRAFT 21-1-22205-001
TABLE 3
ESTIMATED WATER BUDGET FOR PHASE 3 MITIGATION CASES
SHANNON & WILSON, INC.
GW
Inflow
Pond
Overflow
GW
Inflow
Pond
Overflow
GW
Inflow
Pond
Overflow
GW
Inflow
Pond
Overflow
GW
Inflow
Pond
Overflow
Average
annual 150 135 50 35 130-1501 115-1301 180 5 70 0
Normal
winter 255 270 90 105 NA NA 310 35 NA NA
Wet winter 355 405 115 165 NA NA 385 45 NA NA
Notes:
GW = groundwater1 Range for three modeled wall depths.
Units are gallons per minute
NA = not analyzed
Case D – Combined
Grout Window &
RechargeHydrologic
Case
Expanded Phase 3
System
Case A - Grout
Window Case B – Cut-off Wall
Case C – Recharge
Wells
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0
30
-30
-60
-90
-120
-150
-180
B-103 B-104 B-105 B-106(Proj. 35' N.)(Proj. 28' S.)(Proj. 31' N.)(Proj. 9' S.)
West
El
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v
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F
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Previous Ground Surface
(Proj. 31' S.)B-108(Proj. 22' S.)B-107 (Proj. 30' N.)B-109
?
Hb
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(glaciallyoverridden)
Approximate
Location of
Footing
He
Hp
Hp
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50/3"
50/3"
50/6"
67
41
68
50/5"
50/5"
7/24/2003
27
32
45
54
63
50/6"
8/1/2003
64311212422222733
36
39
26
38
43
36
21
5
4
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10
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50/5"
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35
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7/28/2003
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25
30
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21
34
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17
15
29
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39
60
14
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90
50/4"
50/5"
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7/31/2003
36410
41324227
32
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37
32
8/1/2003
553200
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33
20
21
20
7
3232
A
East
A'
323431301281535
56
28
29
31
7/25/2003
B-102
(Proj. 29' S.)
6252
3140
85
41
44
39
37
32
41
45
37
38
15
8
11
0
0
7/23/2003
B-101(Proj. 14' N.)
20851242
431319
34
37
44
32
7/22/2003
PROPOSED
PHASE 3
ROADWAY
B-1
(Proj. 25' N.)B-2(Proj. 18' S.)
B-3
(Proj. 59' N.)
(Moved 5' W.
for Clarity)
13101057ST53
2
7
24
23
23
29
26
26
30
27
20
19
5
2ST0
0
21
15
50/5"
38
15
38
50/5"
67
03-29-16
Ha
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Ha [g]
Ha [g]
He
9422321222511
20
34
31
33
24
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TW
0
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50/6"
50/4.5"
70
6
25
30
66
50/6"
50/5"
07-25-03
He HaHpHpHp
Ha [o]
Existing
Ground
Surface Existing Roadway
Ha
Western Edge of Phase 2
Permeable
Backfill
Permeable
Backfill
Excavated During Phase 2
83433425
3
4ST3
30
31
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36
32
30
33
21
20
18
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03-31-16
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2
15
17
25
25
30
30
30
23
16
19
16
15
12
4
0
04-01-16
90 City of Tukwila Property UPRR
RIGHT-OF-WAY
Current BNSF
Right-of-Way
City of Renton
Right-of-Way
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Ha [g]
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CPT-3(Proj. 245' N.)
CPT-4(Proj. 72' N.)
Ha
Qt (tsf)300
5-26-16
0 Qt (tsf)300
5-26-16
0Qt (tsf)5-26-163000
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6
A
u
t
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:
S
A
C
FIG. 6
SUBSURFACE PROFILE A-A'
SHANNON & WILSON, INC.
Strander Boulevard Extension Phase 3
Preliminary Design - Geotechnical
City of Tukwila, Washington
21-1-22205-001December 2016
Horizontal = Vertical
0 60 120
Scale in Feet
This subsurface profile is generalized from
materials observed in soil borings. Variations
may exist between profile and actual conditions.
NOTE
DRAFT
St
r
a
n
d
e
r
Bo
u
l
e
v
a
r
d
Extension Phase 3 Project
Pr
e
l
i
m
i
n
a
r
y
Design ‐Geotechnical
Ci
t
y
of Tukwila, Washington
CO
N
C
E
P
T
U
A
L
WATER BUDGET FOR PHASE 2 SYSTEM
De
c
e
m
b
e
r
20
1
6
21 ‐1 ‐22205 ‐001
SH
A
N
N
O
N
& WILSON, INC.
Ge
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c
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En
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t
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ConsultantsFIG. 7
Dr
a
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s
= GW
+ RO
P
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OF
= Dr
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I
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DR
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Extension Phase 3 Project
Pr
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l
i
m
i
n
a
r
y
Design ‐Geotechnical
Ci
t
y
of Tukwila, Washington
GR
O
U
N
D
W
A
T
E
R
MODEL DOMAIN,
BO
U
N
D
A
R
Y
CONDITIONS AND LAYERING
De
c
e
m
b
e
r
20
1
6
21 ‐1 ‐22205 ‐001
SH
A
N
N
O
N
& WILSON, INC.
Ge
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c
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n
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En
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ConsultantsFIG. 8
C
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(
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Ph
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(G
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)
250 500
0
Ph
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Ph
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un
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(
o
)
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DR
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Bo
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e
v
a
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d
Extension Phase 3 Project
Pr
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l
i
m
i
n
a
r
y
Design ‐Geotechnical
Ci
t
y
of Tukwila, Washington
PH
A
S
E
3 MODEL COMPUTATIONAL
ME
S
H
,
DR
A
I
N
AREAS AND POND
De
c
e
m
b
e
r
20
1
6
21 ‐1 ‐22205 ‐001
SH
A
N
N
O
N
& WILSON, INC.
Ge
o
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e
c
h
n
i
c
a
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an
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En
v
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m
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t
a
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ConsultantsFIG. 95001,000
25
0
50
0
Ph
a
s
e
2 Dr
a
i
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s
Ph
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3 Dr
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St
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10
0
15
0
20
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0
30
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35
0
40
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Ba
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g
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Extension Phase 3 Project
Pr
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l
i
m
i
n
a
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y
Design ‐Geotechnical
Ci
t
y
of Tukwila, Washington
MO
D
E
L
‐ES
T
I
M
A
T
E
D
GROUNDWATER
IN
F
L
O
W
TO
PHASE 3 UNDERDRAIN SYSTEM
De
c
e
m
b
e
r
20
1
6
21 ‐1 ‐22205 ‐001
SH
A
N
N
O
N
& WILSON, INC.
Ge
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t
e
c
h
n
i
c
a
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an
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En
v
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ConsultantsFIG. 10
No
t
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s
:
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–P
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d
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d
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on
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DR
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a
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Extension Phase 3 Project
Pr
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l
i
m
i
n
a
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y
Design ‐Geotechnical
Ci
t
y
of Tukwila, Washington
MO
D
E
L
‐ES
T
I
M
A
T
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D
OVERFLOW FROM
PH
A
S
E
3 STORMWATER POND
De
c
e
m
b
e
r
20
1
6
21 ‐1 ‐22205 ‐001
SH
A
N
N
O
N
& WILSON, INC.
Ge
o
t
e
c
h
n
i
c
a
l
an
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En
v
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ConsultantsFIG. 11
050
10
0
15
0
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0
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0
30
0
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D
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h
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(
g
p
m
)
To
t
a
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GW
In
f
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to
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r
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(a
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l
hy
d
r
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)
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a
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n
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a
l
hy
d
r
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)
21-1-22205-001
APPENDIX A FIELD EXPLORATION AND HYDROGEOLOGIC DATA
21-1-22205-001_R1_AA_R1_AA/wp/lmr 21-1-22205-001
A-i
APPENDIX A FIELD EXPLORATION AND HYDROGEOLOGIC DATA
TABLE OF CONTENTS Page
A.1 INTRODUCTION .......................................................................................................... A-1
A.2 SUBSURFACE EXPLORATIONS................................................................................ A-1 A.2.1 Soil Boring and Monitoring Wells ................................................................... A-1
A.2.2 Cone Penetrometer Testing (CPT) ................................................................... A-2
A.3 GROUNDWATER AND SURFACE WATER LEVEL MONITORING ..................... A-2
A.4 SINGLE WELL “SLUG” TESTS AND ANALYSIS .................................................... A-3
A.5 GRAIN SIZE ANALYSES............................................................................................. A-4
A.6 REFERENCES ............................................................................................................... A-4
TABLES
A-1 Summary of Slug Test Analyses
A-2 Estimated Hydraulic Conductivity Results for Grain Size Analysis - Phase 3
A-3 Estimated Hydraulic Conductivity Results for Grain Size Analysis - All Results
FIGURES A-1 Soil Description and Log Key (3 sheets)
A-2 Log of Boring B-1 (4 sheets)
A-3 Log of Boring B-2 (4 sheets) A-4 Log of Boring B-3 (5 sheets)
A-5 Groundwater Levels and Green River Stage Data
A-6 Stormwater Pond and Local Precipitation Data
A-7 Slug Test Results B-1-ow (6 sheets)
A-8 Slug Test Results B-2-ow (6 sheets) A-9 Slug Test Results B-3-ow (6 sheets)
21-1-22205-001_R1_AA_R1_AA/wp/lmr 21-1-22205-001
A-1
APPENDIX A FIELD EXPLORATION AND HYDROGEOLOGIC DATA
A.1 INTRODUCTION
This appendix presents our hydrogeologic data and analysis for the proposed Phase 3 design at
the Strander Boulevard Expansion Phase 3 project in Tukwila, Washington. The hydrogeologic
data and analyses includes soil descriptions, groundwater and surface water levels, new
monitoring wells, grain size data and analyses, and slug-test data and analyses used to determine
hydraulic parameters (transmissivity, hydraulic conductivity, and storage coefficients) pertinent
to design and construction.
A.2 SUBSURFACE EXPLORATIONS
A.2.1 Soil Boring and Monitoring Wells
To characterize the subsurface conditions along the proposed Phase 3 alignment, S&W
oversaw the drilling of three soil borings (B-1, B-2 and B-3) (see Figure 2). Holocene Drilling
(Holocene), under contract to S&W, drilled the three borings using mud rotary drilling
techniques between March 28 and April 1, 2016. Borings B-1 and B-2 were drilled to 100 feet
below ground surface (bgs) and B-3 was drilled to 141.5 feet bgs. We obtained disturbed
samples in conjunction with the Standard Penetration Test typically at 2.5-foot intervals to 20
feet bgs and then at a 5-foot interval for the remaining sample. We submitted soil samples to our
Seattle laboratory for geotechnical testing. Following the drilling, Holocene installed the
following:
Two-inch-diameter observation wells - in borings B-1 (B-1-ow) screened from 45 to 55 feet bgs); boring B-2 (B-2-ow) screened from 35 to 45 feet bgs;
and boring B-3 (B-3-ow) screened from 45 to 55 feet bgs).
Vibrating wireline piezometers (VWPs) - in boring B-2 (B-2-vwp) at 10 feet
bgs; and in boring B-3 (B-3-vwp) at 120 feet bgs.
We performed well development using an inertia pump with a check valve to agitate and
remove the fines surrounding the well. Well development increases the hydraulic connection
between the well and the aquifer by reducing skin effects from drilling and removing fines from
the filter pack and formation adjacent to the well screen.
Figure A-1 shows the soil classification system used, and Figures A-2, A-3 and A-4 are
the soil boring and well completion logs for borings B-1, B-2, and B-3, respectively.
21-1-22205-001_R1_AA_R1_AA/wp/lmr 21-1-22205-001
A-2
A.2.2 Cone Penetrometer Testing (CPT)
On May 26, 016, In Situ Engineering (under contract to S&W) completed five CPTs
(CPT-01 though CPT-05) using a truck mounted rig. Figure 3 shows the CPT locations. The
CPTs were advanced to 80 feet bgs. The CPT method consists of pushing an instrumented cone
into the ground to obtain measurements of tip resistance, friction resistance, and pore water
pressure. CPT data can be used to estimate soil parameters for use in engineering studies. The
CPT develops a nearly continuous subsurface profile at a particular location, but does not
retrieve a soil sample for laboratory testing. The full CPT report is included in this appendix.
A.3 GROUNDWATER AND SURFACE WATER LEVEL MONITORING
We installed pressure transducer/data logger equipment in three Phase 3 monitoring wells B-1-
ow, B-2-ow and B-3-ow shortly after construction and development in April 2016. We also
connected data loggers to VWPs B-2-vwp and B-3-vwp in April 2016. The data loggers have
collected groundwater level readings at 15 minute intervals. In May 2016, we installed a
temporary staff gauge and pressure transducer/data loggers near the south end of the stormwater
pond and in the adjacent wetland area to record water level changes (shown on Figure 3). We
downloaded on-line river stage data for the Green River at Tukwila for the U.S. Geological
Survey’s station #12113350 (http://waterdata.usgs.gov/nwis/uv?site_no=12113350) for the study
period.
Figure A-5 shows the groundwater level data for at the wells and Green River during the
monitoring period. Figure A-6 shows the surface water monitoring data for the pond, wetlands,
and the daily precipitation data for the Renton Airport station. The following are our
observations:
The highest groundwater elevations were recorded in shallow B-2-vwp. Levels
ranged from elevation 21.5 feet (in April 2016) to below elevation 17 feet when the
probe became dry (from July 23 through October 17, 2016).
In the three monitoring wells completed in the upper Ha unit (B-1-ow, B-2-ow, and
B-3-ow), groundwater levels ranged from a high of 13 feet (in April 2016) to 9 feet (in September 2016). The groundwater elevation in well B-3-ow (closest to the Phase
drain) was consistently the lowest, whereas the groundwater elevation in well B-1-ow
(closest to the Green River) was the highest.
In the deep B-3-vwp, the groundwater elevations ranged from elevation 12.5 feet (in
April 2016) to elevation 9.25 feet (in August 2016). The levels were slightly higher than in the three shallow wells in the summer but lower in the spring and fall.
21-1-22205-001_R1_AA_R1_AA/wp/lmr 21-1-22205-001
A-3
The Green River level was typically between one and two feet higher than groundwater levels in upper Ha aquifer in the summer, but was up to four feet higher during the wet period in October 2016.
The pond and wetland stage levels generally declined during the summer, and the
wetland probe went dry in early July 2016. The heavy rain during October 2016
resulted in the pond level rising by up to 0.5 feet and the probe in the wetland becoming wet again.
A.4 SINGLE WELL “SLUG” TESTS AND ANALYSIS
We conducted single-well slug tests in monitoring wells B-1-ow, B-2-ow and B-3-ow to estimate
in situ, horizontal hydraulic conductivity (Kh) for the shallow alluvial aquifer. Slug testing
consists of rapidly raising or lowering the water level within a monitoring well and measuring,
over time, the water-level recovery (rising or falling head) to static conditions. The water level
in the well is displaced by putting a slug (a sealed, sand-filled, polyvinyl chloride pipe) into the
water column. The water-level recovery is measured using a pressure transducer and datalogger
system. Both rising- and falling-head tests were performed as part of the slug testing. The data
obtained from the rising-head and falling-head slug tests were plotted as semi-log graphs of
water-level change versus time.
Figures A-7, A-8 and A-9 show the slug-test data and interpretation plots. We analyzed the data
using the Bouwer and Rice (Bouwer 1989) method. We obtained acceptable matches for the
observed data for all tests. Table A-1 presents the results of our analyses. The following
summarizes the results of the test interpretation:
The range of all calculated Kh is from 6 to 60 ft/day.
The geometric mean Kh values for the three wells (six tests each) are:
o B-1-ow = 33 ft/d (1.2 x 10-2 cm/sec) o B-2-ow = 48 ft/day (1.7 x 10-2 cm/sec) o B-3-ow = 9 ft/day (3.3 x 10-3 cm/sec)
As slug tests have a relatively small radius of influence, they do not provide data regarding large-
scale aquifer properties, aquifer geometry, or boundary conditions affecting groundwater flow.
Pumping tests can provide data related to large-scale aquifer properties. Although a pumping
test was not performed for this exploration phase, S&W did conduct and analyzed a pumping test
using well PW-1 in 2010 (S&W, 2011). This test produced a range of hydraulic conductivities
for the Ha unit of 48 to 125 ft/day (1.7 x 10-2 to 4.4 x 10-2 cm/sec). Therefore, the slug test
results for hydraulic conductivity are towards the low end of the range derived from the pumping
test.
21-1-22205-001_R1_AA_R1_AA/wp/lmr 21-1-22205-001
A-4
A.5 GRAIN SIZE ANALYSES
We performed grain size analyses on 17 soil samples collected between 7.5 and 95 feet below
ground surface from the three Phase 3 project borings. Figures included in Appendix B show the
grain size distribution plots. We collected grain size analysis data for 23 other soil samples
collected during previous phase boring (S&W, 2004; S&W, 2010). We analyzed both sets of
data using four empirical methods to estimate hydraulic conductivity (K), including Hazen,
Kozeny-Carmen, Breyer and Slitcher. All of the methods are described in the journal article,
“Evaluation of Empirical Formulae for Determination of Hydraulic Conductivity Based on Grain
Size Analysis” (Odong 2007). All of the methods use the D10 (10 percent finer by weight) from
the grain size distribution plots to calculate the hydraulic conductivity of the soil.
Tables A-2 and A-3 present the hydraulic conductivity value calculated using each of the
methods and the average hydraulic conductivity values for all four methods for the Phase 3
(Table A-2) and for the previous soil samples (Table A-3). These results indicate the following:
The results for the six samples from the He and Ha(o) units had the largest range and
a relatively low average K (0.04 ft/day). However, three samples had results
significantly higher than the average K (between 0.1 to 0.4 ft/day).
The results for the nine samples collected from borings B-1, B-2 and B-3 from the upper Ha unit had a relatively small K range (22 to 66 ft/day). This range is within
the range for the previous samples (1.1 to 88 ft/day) and similar to the range obtained
for the slug tests in the three monitoring wells completed in this unit (9 to 48 ft/day;
Table A-1).
The two samples from borings B-1 and B-2 in the lower Ha unit (both described as silt) had K values less than 0.005 ft/day. These results indicate that this soil unit
could be acting locally as a lower confining unit for the upper Ha unit.
The K values for the eight deep soil samples (between 75 and 180 feet) collected
during the previous explorations from the lower Ha unit ranged from 1.2 to 10 ft/day.
The estimated average K from all grain size data interpretation for the upper Ha unit at the
project site is 23 ft/day. This average is similar to the hydraulic conductivity values obtained for
the slug tests performed in wells B-1-ow and B-2-ow (33 and 48 ft/day, respectively) but higher
than the average for well B-3-ow (9 ft/day).
A.6 REFERENCES
Bouwer, Herman, 1989, The Bouwer and Rice slug test – an update: Ground Water, v. 27, no. 3, p. 304-309.
21-1-22205-001_R1_AA_R1_AA/wp/lmr 21-1-22205-001
A-5
Odong, Justine, 2007, Evaluation of empirical formulae for determination of hydraulic conductivity based on grain-size analysis: The Journal of American Science, v. 3, no. 3, p. 54-60, available: http://www.jofamericanscience.org/journals/am-sci/0303/.
Shannon & Wilson, Inc., 2011, Strander Boulevard underpass phase II, revised dewatering
evaluation: Report prepared by Shannon & Wilson, Inc., Seattle, Wash., 21-1-21292-003,
for Berger/ABAM, Federal Way, Wash., May.
TABLE A-1
SUMMARY OF SLUG TEST ANALYSES
SHANNON & WILSON, INC.
feet to feet feet feet cm/sec ft/d
FHT1 9.2E-03 26
FHT2 1.1E-02 31
FHT3 8.4E-03 24
RHT1 1.4E-02 40
RHT2 1.6E-02 45
RHT3 1.4E-02 40
Average 1.2E-02 33
FHT1 1.4E-02 40
FHT2 1.6E-02 45
FHT3 1.4E-02 40
RHT1 2.0E-02 57
RHT2 2.1E-02 60
RHT3 1.8E-02 51
Average 1.7E-02 48
FHT1 2.4E-03 7
FHT2 3.0E-03 9
FHT3 2.1E-03 6
RHT1 4.2E-03 12
RHT2 4.3E-03 12
RHT3 3.7E-03 10
Average 3.3E-03 9
Notes:
1 - recorded on April 6, 2016
Hydraulic conductivities estimated from slug test results using Bouwer and Rice (1976) method.
cm/sec = centimeters per second; ft/day = feet per day
USCS = Unified Soil Classification System
Calculated Hydraulic
Conductivity
B-1-ow 45.0 to 55.0 SP-SM 28.0 12.9
Well ID
Screen Depth USCS
Description(s)
Reference
Elevation
Static Water
Elevation1
Test ID
12.7
B-3-ow 45.0 to 55.0 SP-SM 27.5 12.3
B-2-ow 35.0 to 45.0 SP 27.0
Appendix A - tables 21-1-22205-001DRAFT
TABLE A-2
GRAIN SIZE ANALYSIS FOR PHASE 3 BORINGS
SHANNON & WILSON, INC.
Hazen
Kozeny-
Carman Breyer Slitcher
ft cm/sec cm/sec cm/sec cm/sec cm/sec ft/d
B-2 S-3 7.5 ML 8.3 NA 3.5E-05 NA NA 3.5E-05 0.1
B-1 S-4 10 SM 6.7 NA 1.2E-04 NA 4.9E-05 8.7E-05 0.2
B-2 S-5 12.5 SM 5.7 NA 2.0E-04 NA 7.5E-05 1.4E-04 0.4
B-1 S-7 17.5 ML 14.2 NA 9.5E-06 NA NA 9.5E-06 0.03
B-3 S-8 20 SM 28.0 NA 2.1E-05 NA 9.7E-06 1.6E-05 0.04
B-1 S-10 30 ML 17.5 NA 1.8E-07 NA NA 1.8E-07 0.001
1.5E-05 0.04
B-2 S-12 40 SP-SM 2.9 2.8E-02 2.9E-02 2.6E-02 9.7E-03 2.3E-02 65.6
B-3 S-12 40 SP-SM 3.5 1.9E-02 1.8E-02 1.8E-02 6.3E-03 1.6E-02 44.0
B-1 S-14 45 SP-SM 2.8 1.3E-02 1.4E-02 1.2E-02 4.5E-03 1.1E-02 30.7
B-2 S-14 50 SP-SM 2.4 1.3E-02 1.5E-02 1.2E-02 4.7E-03 1.1E-02 31.2
B-3 S-14 50 SP-SM 2.6 1.8E-02 2.0E-02 1.6E-02 6.4E-03 1.5E-02 42.6
B-1 S-16 55 SP-SM 2.7 NA 1.1E-02 9.0E-03 NA 9.9E-03 28.0
B-2 S-16 60 SP-SM 2.3 NA 1.2E-02 9.0E-03 NA 1.0E-02 29.3
B-1 S-18 65 SM 2.4 NA 8.5E-03 6.7E-03 NA 7.6E-03 21.5
B-3 S-17 65 SP-SM 2.6 1.5E-02 1.6E-02 1.3E-02 5.3E-03 1.3E-02 35.5
1.2E-02 34.7
B-2 S-21 85 ML 30.0 NA 1.5E-06 NA NA 1.5E-06 4.E-03
B-1 S-24 95 ML 26.5 NA 7.2E-07 NA NA 7.2E-07 2.E-03
1.1E-06 0.003
Notes:
Analytical methods are summarized in Odong, 2007.
cm/sec = centimeters per second
Cu = uniformity coefficient (d60/d10)
ft/d = feet per day
ID = identification
NA = not applicable
USCS = Unified Soil Classification System
Geomean
Average of Valid
Analytical Methods
He and Ha(o) Units
Geomean
Upper Ha Ulluvium Unit
Lower Ha Alluvium Unit
Geomean
Boring ID
Sample
ID
Sample
Depth USCS
Description
Cu Ratio
(Coefficient
of
Uniformity)
Analytical Method
Appendix A - tables/wp/lk 21-1-22205-001DRAFT
TABLE A-3
GRAIN SIZE ANALYSIS FOR PREVIOUS BORINGS
SHANNON & WILSON, INC.
Hazen
Kozeny-
Carman Breyer Slitcher
ft cm/sec cm/sec cm/sec cm/sec cm/sec ft/d
B-104 S-11 27.5 SM 7.8 NA 8.7E-04 NA NA 8.7E-04 2.5
B-107 S-12 30 SP-SM 4.8 1.7E-02 1.3E-02 1.7E-02 NA 1.6E-02 44.4
B-109 S-12 30 SP-SM 2.8 2.4E-02 2.6E-02 2.2E-02 8.5E-03 2.4E-02 68.5
MW-3 S-6 30 SP-SM 5.6 NA 6.3E-03 9.3E-03 NA 7.8E-03 22.2
B-108 S-13 35 SP-SM 3.9 1.2E-02 1.1E-02 1.2E-02 NA 1.1E-02 32.5
MW-4 S-7 35 SP-SM 4.6 9.9E-03 7.9E-03 9.9E-03 NA 9.2E-03 26.2
B-301 S-15 37.5 SP-SM 3.0 1.2E-02 1.3E-02 1.1E-02 NA 1.2E-02 34.1
B-105 S-14 40 SP 2.1 3.6E-02 4.4E-02 3.2E-02 1.4E-02 3.1E-02 88.4
B-103 S-16 50 SP-SM 3.2 1.7E-02 1.7E-02 1.6E-02 5.6E-03 1.4E-02 38.8
B-106 S-16 50 SM 9.7 NA 3.9E-04 NA NA 3.9E-04 1.1
MW-4 S-10 50 SW-SM 9.6 NA 1.1E-03 2.5E-03 NA 1.8E-03 5.1
MW-1 S-11 55 SP-SM 3.0 NA 1.0E-02 9.2E-03 NA 9.8E-03 27.8
MW-3 S-11 55 SM 7.4 NA 1.4E-03 NA NA 1.4E-03 4.0
B-102 S-20 70 SP-SM 2.7 NA 1.1E-02 9.4E-03 NA 1.0E-02 29.1
6.3E-03 17.7
B-109 S-22 75 SP-SM 5.8 NA 2.7E-03 4.1E-03 NA 3.4E-03 9.6
B-107 S-22 80 SM 8.7 NA 4.3E-04 NA NA 4.3E-04 1.2
MW-3 S-19 95 SP-SM 6.8 NA 2.2E-03 3.9E-03 NA 3.1E-03 8.8
B-301 S-30 112.5 SW-SM 74.3 NA 1.2E-03 NA NA 1.2E-03 3.4
B-103 S-31 120 GW-GM 77.0 NA 2.4E-03 NA NA 2.4E-03 6.9
B-105 S-31 120 SW-SM 22.7 NA 2.0E-03 NA NA 2.0E-03 5.6
B-105 S-35 140 SP-SM 98.0 NA 6.1E-04 NA NA 6.1E-04 1.7
B-103 S-43 180 SW-SM 13.5 NA 5.2E-04 NA NA 5.2E-04 1.5
1.3E-03 3.7
Notes:
Analytical methods are summarized in Odong, 2007.
cm/sec = centimeters per second
Cu = uniformity coefficient (d60/d10)
ft/d = feet per day
ID = identification
NA = not applicable
USCS = Unified Soil Classification System
Average of Valid
Analytical Methods
Upper Ha Alluvium Unit
Geomean
Lower Ha Alluvium Unit
Geomean
Boring ID
Sample
ID
Sample
Depth USCS
Description
Cu Ratio
(Coefficient
of
Uniformity)
Analytical Method
Appendix A - tables/wp/lk 21-1-22205-001DRAFT
December 2016 21-1-22205-001
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
1Gravel, sand, and fines estimated by mass. Other constituents, such asorganics, cobbles, and boulders, estimated by volume.
2Reprinted, with permission, from ASTM D2488 - 09a Standard Practice forDescription and Identification of Soils (Visual-Manual Procedure), copyrightASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. Acopy of the complete standard may be obtained from ASTM International,www.astm.org.
140 pounds with a 30-inch free fall.Rope on 6- to 10-inch-diam. cathead2-1/4 rope turns, > 100 rpm
NOTE: If automatic hammers areused, blow counts shown on boringlogs should be adjusted to account forefficiency of hammer.
10 to 30 inches longShoe I.D. = 1.375 inchesBarrel I.D. = 1.5 inchesBarrel O.D. = 2 inches
Sum blow counts for second and third6-inch increments.Refusal: 50 blows for 6 inches orless; 10 blows for 0 inches.
RELATIVE
CONSISTENCY
N, SPT,
BLOWS/FT.5% to 12%
fine-grained:
with Silt orwith Clay 3
15% or more of asecond coarse-grained constituent:with Sand or
with Gravel 5
< 5%
5 to 10%
15 to 25%
30 to 45%
50 to 100%
Surface CementSeal
Asphalt or Cap
Slough
Inclinometer or
Non-perforated Casing
Vibrating WirePiezometer
N, SPT,
BLOWS/FT.
< 4
4 - 10
10 - 30
30 - 50
> 50
DESCRIPTION
< #200 (0.075 mm = 0.003 in.)
#200 to #40 (0.075 to 0.4 mm; 0.003 to 0.02 in.)
#40 to #10 (0.4 to 2 mm; 0.02 to 0.08 in.)
#10 to #4 (2 to 4.75 mm; 0.08 to 0.187 in.)
SIEVE NUMBER AND/OR APPROXIMATE SIZE
#4 to 3/4 in. (4.75 to 19 mm; 0.187 to 0.75 in.)
3/4 to 3 in. (19 to 76 mm)
3 to 12 in. (76 to 305 mm)
> 12 in. (305 mm)
Fine
Coarse
Fine
Medium
Coarse
BOULDERS
COBBLES
GRAVEL
FINES
SAND
Sheet 1 of 3
CONSTITUENT2
SOIL DESCRIPTIONAND LOG KEY
SHANNON & WILSON, INC.Geotechnical and Environmental Consultants
Absence of moisture, dusty, dryto the touch
Damp but no visible water
Visible free water, from belowwater table
FIG. A-1
Shannon & Wilson, Inc. (S&W), uses a soilidentification system modified from the Unified Soil
Classification System (USCS). Elements of the
USCS and other definitions are provided on this
and the following pages. Soil descriptions arebased on visual-manual procedures (ASTM
D2488) and laboratory testing procedures (ASTM
D2487), if performed.
STANDARD PENETRATION TEST (SPT)
SPECIFICATIONS
Hammer:
Sampler:
N-Value:
Dry
Moist
Wet
MOISTURE CONTENT TERMS
Modifying
(Secondary)
Precedes majorconstituent
Major
MinorFollows majorconstituent
1All percentages are by weight of total specimen passing a 3-inch sieve.2The order of terms is: Modifying Major with Minor.3Determined based on behavior.4Determined based on which constituent comprises a larger percentage.5Whichever is the lesser constituent.
COARSE-GRAINEDSOILS(less than 50% fines)1
NOTE: Penetration resistances (N-values) shown on boring logs are as recorded in the field and have not been corrected for hammer efficiency, overburden, or other factors.
PARTICLE SIZE DEFINITIONS
RELATIVE DENSITY / CONSISTENCYSand or Gravel 4
30% or morecoarse-grained:Sandy or Gravelly 4
More than 12%fine-grained:Silty or Clayey 3
15% to 30%
coarse-grained:
with Sand orwith Gravel 4
30% or more total
coarse-grained andlesser coarse-grained constituentis 15% or more:
with Sand orwith Gravel 5
Very soft
Soft
Medium stiff
Stiff
Very stiff
Hard
Very loose
Loose
Medium dense
Dense
Very dense
RELATIVE
DENSITY
FINE-GRAINED SOILS(50% or more fines)1
COHESIVE SOILS
< 2
2 - 4
4 - 8
8 - 15
15 - 30
> 30
COHESIONLESS SOILS
Silt, Lean Clay,Elastic Silt, orFat Clay 3
PERCENTAGES TERMS 1, 2
Trace
Few
Little
Some
Mostly
WELL AND BACKFILL SYMBOLS
BentoniteCement Grout
Bentonite Grout
Bentonite Chips
Silica Sand
Perforated orScreened Casing
S&W INORGANIC SOIL CONSTITUENT DEFINITIONS
SO
I
L
_
C
L
A
S
S
_
K
E
Y
_
P
G
1
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
6
/
1
6
December 2016 21-1-22205-001
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
GC
SC
Inorganic
Organic
(more than 50%of coarse fractionretained on No. 4sieve)
MAJOR DIVISIONS GROUP/GRAPHICSYMBOL
CH
OH
ML
CL
TYPICAL IDENTIFICATIONS
Gravel
Sand
Silty Sand; Silty Sand with Gravel
Clayey Sand; Clayey Sand with Gravel
Clayey Gravel; Clayey Gravel with Sand
Sheet 2 of 3
Gravels
Primarily organic matter, dark incolor, and organic odor
SW
(more than 12%fines)
Silts and Clays
Silts and Clays
(more than 50%retained on No.200 sieve)
(50% or more ofcoarse fractionpasses the No. 4sieve)
(liquid limit lessthan 50)
(liquid limit 50 ormore)
Organic
Inorganic
FINE-GRAINEDSOILS
SM
Sands
Silty or ClayeyGravel
Silt; Silt with Sand or Gravel; Sandy orGravelly Silt
Organic Silt or Clay; Organic Silt or Claywith Sand or Gravel; Sandy or GravellyOrganic Silt or Clay
HIGHLY-ORGANIC SOILS
COARSE-GRAINEDSOILS
OL
(less than 5%fines)
GW
Geotechnical and Environmental ConsultantsSHANNON & WILSON, INC.
(less than 5%fines)
PT
FIG. A-1
(more than 12%fines)
MH
SP
GP
GM
Silty or ClayeySand
Silty Gravel; Silty Gravel with Sand
(50% or morepasses the No. 200sieve)
SOIL DESCRIPTIONAND LOG KEY
Elastic Silt; Elastic Silt with Sand orGravel; Sandy or Gravelly Elastic Silt
Fat Clay; Fat Clay with Sand or Gravel;Sandy or Gravelly Fat Clay
Organic Silt or Clay; Organic Silt or Claywith Sand or Gravel; Sandy or GravellyOrganic Silt or Clay
Poorly Graded Sand; Poorly GradedSand with Gravel
Well-Graded Sand; Well-Graded Sandwith Gravel
Well-Graded Gravel; Well-GradedGravel with Sand
Poorly Graded Gravel; Poorly GradedGravel with Sand
Lean Clay; Lean Clay with Sand orGravel; Sandy or Gravelly Lean Clay
Peat or other highly organic soils (seeASTM D4427)
NOTES
1.Dual symbols (symbols separated by a hyphen, i.e., SP-SM, Sand with
Silt) are used for soils with between 5% and 12% fines or when the
liquid limit and plasticity index values plot in the CL-ML area of the
plasticity chart. Graphics shown on the logs for these soil types are a
combination of the two graphic symbols (e.g., SP and SM).
2.Borderline symbols (symbols separated by a slash, i.e., CL/ML, Lean
Clay to Silt; SP-SM/SM, Sand with Silt to Silty Sand) indicate that the
soil properties are close to the defining boundary between two groups.
SO
I
L
_
C
L
A
S
S
_
K
E
Y
_
P
G
2
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
6
/
1
6
NOTE: No. 4 size = 4.75 mm = 0.187 in.; No. 200 size = 0.075 mm = 0.003 in.
UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
(Modified From USACE Tech Memo 3-357, ASTM D2487, and ASTM D2488)
December 2016 21-1-22205-001
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
SHANNON & WILSON, INC.Geotechnical and Environmental Consultants FIG. A-1
Sheet 3 of 3
SOIL DESCRIPTIONAND LOG KEY
1Reprinted, with permission, from ASTM D2488 - 09a Standard Practice for
Description and Identification of Soils (Visual-Manual Procedure), copyright ASTMInternational, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the
complete standard may be obtained from ASTM International, www.astm.org.
2Adapted, with permission, from ASTM D2488 - 09a Standard Practice for
Description and Identification of Soils (Visual-Manual Procedure), copyright ASTM
International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the
complete standard may be obtained from ASTM International, www.astm.org.
Interbedded
Laminated
Fissured
Slickensided
Blocky
Lensed
Homogeneous
ATD
Diam.
Elev.
ft.
FeO
gal.
Horiz.
HSA
I.D.
in.
lbs.
MgO
mm
MnO
NA
NP
O.D.
OW
pcf
PID
PMT
ppm
psi
PVC
rpm
SPT
USCS
qu
VWP
Vert.
WOH
WOR
Wt.
Crumbles or breaks with handling or slightfinger pressure.Crumbles or breaks with considerable fingerpressure.Will not crumble or break with finger pressure.
PLASTICITY2
CEMENTATION TERMS1
GRADATION TERMS
STRUCTURE TERMS1
ACRONYMS AND ABBREVIATIONS
Alternating layers of varying material orcolor with layers at least 1/4-inch thick;singular: bed.Alternating layers of varying material orcolor with layers less than 1/4-inch thick;singular: lamination.Breaks along definite planes or fractureswith little resistance.Fracture planes appear polished or glossy;sometimes striated.Cohesive soil that can be broken down intosmall angular lumps that resist furtherbreakdown.Inclusion of small pockets of different soils,such as small lenses of sand scatteredthrough a mass of clay.Same color and appearance throughout.
Narrow range of grain sizes present or, withinthe range of grain sizes present, one or moresizes are missing (Gap Graded). Meets criteriain ASTM D2487, if tested.Full range and even distribution of grain sizespresent. Meets criteria in ASTM D2487, iftested.
Poorly Graded
Well-Graded
Weak
Moderate
Strong
Irregular patches of different colors.
Soil disturbance or mixing by plants or animals.
Nonsorted sediment; sand and gravel in siltand/or clay matrix.
Material brought to surface by drilling.
Material that caved from sides of borehole.
Disturbed texture, mix of strengths.
VISUAL-MANUAL CRITERIA
A 1/8-in. thread cannot be rolled atany water content.A thread can barely be rolled anda lump cannot be formed whendrier than the plastic limit.A thread is easy to roll and notmuch time is required to reach theplastic limit. The thread cannot bererolled after reaching the plasticlimit. A lump crumbles when drierthan the plastic limit.It takes considerable time rollingand kneading to reach the plasticlimit. A thread can be rerolledseveral times after reaching theplastic limit. A lump can beformed without crumbling whendrier than the plastic limit.
Sharp edges and unpolished planar surfaces.
Similar to angular, but with rounded edges.
Nearly planar sides with well-rounded edges.
Smoothly curved sides with no edges.
Width/thickness ratio > 3.
Length/width ratio > 3.
PARTICLE ANGULARITY AND SHAPE TERMS1
ADDITIONAL TERMS
Angular
Subangular
Subrounded
Rounded
Flat
Elongated
DESCRIPTION
Nonplastic
Low
Medium
High
At Time of Drilling
Diameter
Elevation
Feet
Iron Oxide
Gallons
Horizontal
Hollow Stem Auger
Inside Diameter
Inches
Pounds
Magnesium Oxide
Millimeter
Manganese Oxide
Not Applicable or Not Available
Nonplastic
Outside Diameter
Observation Well
Pounds per Cubic Foot
Photo-Ionization Detector
Pressuremeter Test
Parts per Million
Pounds per Square Inch
Polyvinyl Chloride
Rotations per Minute
Standard Penetration Test
Unified Soil Classification System
Unconfined Compressive Strength
Vibrating Wire Piezometer
Vertical
Weight of Hammer
Weight of Rods
WeightMottled
Bioturbated
Diamict
Cuttings
Slough
Sheared
APPROX.PLASITICITYINDEXRANGE< 4
4 to 10
10 to 20
> 20
SO
I
L
_
C
L
A
S
S
_
K
E
Y
_
P
G
3
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
6
/
1
6
0.2
1.0
12.0
20.0
23.0
1
2
3
4
5
6
7
8
9
4/
1
9
/
2
0
1
6
Asphalt.
Brown, Silty Gravel with Sand (GM); moist;
road subgrade.
Fill (Hf)
Very loose to loose, red-brown to dark
gray-brown, Silty Sand (SM); moist; fine sand;
trace iron-oxide staining; trace fine organics.
Overbank Alluvium (Ha[o])
- Wet at 10 feet.
Very loose to loose, dark gray-brown, Sandy
Silt (ML); wet; fine sand; nonplastic fines;
some fine to coarse organics and wood,
mostly organics in beds; organic odor.
Overbank Alluvium (Ha[o])
Loose, dark gray, Poorly Graded Sand (SP);
wet; fine to medium sand; mostly wood
fragments.
Alluvium (Ha)
Note: Layer description based on poor sample
recovery.
Soft, gray, Organic Silt (OH) to Elastic Silt
(MH); wet; trace fine sand; high plasticity, slow
to rapid dilatancy fines; few to some fine to
coarse organics, mostly organics in
1-inch-thick beds; laminated.
Estuarine (He)
*
Du
r
i
n
g
D
r
i
l
l
i
n
g
De
p
t
h
,
f
t
.
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
De
p
t
h
,
f
t
.
5
10
15
20
25
Well Screen and Sand Filter
Drilling Method:
Drilling Company:
Drill Rig Equipment:
Other Comments:
Lo
g
:
J
M
W
Northing:
Easting:
Station:
Offset:
SOIL DESCRIPTION
20 40 60
Sa
m
p
l
e
s
6 in.
NWJ
Automatic
Refer to the report text for a proper understanding of thesubsurface materials and drilling methods. The stratificationlines indicated below represent the approximate boundariesbetween material types, and the transition may be gradual.
*
LOG OF BORING B-1
0 60
0
Total Depth:
Top Elevation:
Vert. Datum:
Horiz. Datum:
Ground Water Level ATD
Gr
o
u
n
d
Wa
t
e
r
NOTES
CONTINUED NEXT SHEET
20 40
2.0" O.D. Split Spoon Sample
3" O.D. Thin-Walled Tube Bentonite Chips/Pellets
Bentonite Grout
Hole Diam.:
Rod Diam.:
Hammer Type:
LEGEND
Sy
m
b
o
l
Ground Water Level in Well
1. Refer to KEY for explanation of symbols, codes, abbreviations and definitions.
2. Groundwater level, if indicated above, is for the date specified and may vary.
3. USCS designation is based on visual-manual classification and selected lab testing.
Mud Rotary
Holocene Drilling
Mobile B-59
FIG. A2SHANNON & WILSON, INC.
101.5 ft.
~ 28 ft.
Sheet 1 of 4
Re
v
:
J
M
W
December 2016 21-1-22205-001
Ty
p
:
L
K
N
Geotechnical and Environmental Consultants
Sample Not Recovered
Bentonite-Cement Grout
REV 1 - Log in ProgressMA
S
T
E
R
_
L
O
G
_
E
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
4
/
1
6
PENETRATION RESISTANCE
Hammer Wt. & Drop:
(blows/foot)
140 lbs / 30 inches
Plastic Limit
Natural Water Content
% Water Content
Liquid Limit
% Fines (<0.075mm)
WC=71
WC=76LL=86
91
38.0
10
11
12
13
14
15
16
Medium dense to dense, dark gray, Poorly
Graded Sand with Silt (SP-SM); wet; fine sand.
Alluvium (Ha)
*
De
p
t
h
,
f
t
.
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
De
p
t
h
,
f
t
.
35
40
45
50
55
Well Screen and Sand Filter
Drilling Method:
Drilling Company:
Drill Rig Equipment:
Other Comments:
Lo
g
:
J
M
W
Northing:
Easting:
Station:
Offset:
SOIL DESCRIPTION
20 40 60
Sa
m
p
l
e
s
6 in.
NWJ
Automatic
Refer to the report text for a proper understanding of thesubsurface materials and drilling methods. The stratificationlines indicated below represent the approximate boundariesbetween material types, and the transition may be gradual.
*
LOG OF BORING B-1
0 60
0
Total Depth:
Top Elevation:
Vert. Datum:
Horiz. Datum:
Ground Water Level ATD
Gr
o
u
n
d
Wa
t
e
r
NOTES
CONTINUED NEXT SHEET
20 40
2.0" O.D. Split Spoon Sample
3" O.D. Thin-Walled Tube Bentonite Chips/Pellets
Bentonite Grout
Hole Diam.:
Rod Diam.:
Hammer Type:
LEGEND
Sy
m
b
o
l
Ground Water Level in Well
1. Refer to KEY for explanation of symbols, codes, abbreviations and definitions.
2. Groundwater level, if indicated above, is for the date specified and may vary.
3. USCS designation is based on visual-manual classification and selected lab testing.
Mud Rotary
Holocene Drilling
Mobile B-59
FIG. A2SHANNON & WILSON, INC.
101.5 ft.
~ 28 ft.
Sheet 2 of 4
Re
v
:
J
M
W
December 2016 21-1-22205-001
Ty
p
:
L
K
N
Geotechnical and Environmental Consultants
Sample Not Recovered
Bentonite-Cement Grout
REV 1 - Log in ProgressMA
S
T
E
R
_
L
O
G
_
E
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
4
/
1
6
PENETRATION RESISTANCE
Hammer Wt. & Drop:
(blows/foot)
140 lbs / 30 inches
Plastic Limit
Natural Water Content
% Water Content
Liquid Limit
% Fines (<0.075mm)
91
73.0
17
18
19
20
21
22
- Silty layer at 65 feet.
- Silty laminations at 70 feet.
Medium dense, gray, Silty Sand (SM) and
Sandy Silt (ML); wet; fine sand; nonplastic
fines, medium plasticity fines in beds; trace to
few organics.
Overbank Alluvium (Ha[o])
- Peat seams at 85 feet.
De
p
t
h
,
f
t
.
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
De
p
t
h
,
f
t
.
65
70
75
80
85
Well Screen and Sand Filter
Drilling Method:
Drilling Company:
Drill Rig Equipment:
Other Comments:
Lo
g
:
J
M
W
Northing:
Easting:
Station:
Offset:
SOIL DESCRIPTION
20 40 60
Sa
m
p
l
e
s
6 in.
NWJ
Automatic
Refer to the report text for a proper understanding of thesubsurface materials and drilling methods. The stratificationlines indicated below represent the approximate boundariesbetween material types, and the transition may be gradual.
*
LOG OF BORING B-1
0 60
0
Total Depth:
Top Elevation:
Vert. Datum:
Horiz. Datum:
Ground Water Level ATD
Gr
o
u
n
d
Wa
t
e
r
NOTES
CONTINUED NEXT SHEET
20 40
2.0" O.D. Split Spoon Sample
3" O.D. Thin-Walled Tube Bentonite Chips/Pellets
Bentonite Grout
Hole Diam.:
Rod Diam.:
Hammer Type:
LEGEND
Sy
m
b
o
l
Ground Water Level in Well
1. Refer to KEY for explanation of symbols, codes, abbreviations and definitions.
2. Groundwater level, if indicated above, is for the date specified and may vary.
3. USCS designation is based on visual-manual classification and selected lab testing.
Mud Rotary
Holocene Drilling
Mobile B-59
FIG. A2SHANNON & WILSON, INC.
101.5 ft.
~ 28 ft.
Sheet 3 of 4
Re
v
:
J
M
W
December 2016 21-1-22205-001
Ty
p
:
L
K
N
Geotechnical and Environmental Consultants
Sample Not Recovered
Bentonite-Cement Grout
REV 1 - Log in ProgressMA
S
T
E
R
_
L
O
G
_
E
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
4
/
1
6
PENETRATION RESISTANCE
Hammer Wt. & Drop:
(blows/foot)
140 lbs / 30 inches
Plastic Limit
Natural Water Content
% Water Content
Liquid Limit
% Fines (<0.075mm)
90.0
98.0
101.5
23
24
25
Medium stiff, dark gray-brown Silt with Sand
(ML) to Sandy Silt (ML); wet; fine sand; low
plasticity fines, nonplastic beds; few to little
organics, mostly organics in beds; silty sand
beds less than 3 inches thick.
Overbank Alluvium (Ha[o])
Soft, gray-brown, Silt (ML); wet; medium
plasticity fines; sand laminations.
Estuarine (He)
BOTTOM OF BORING
COMPLETED 3/31/2016
De
p
t
h
,
f
t
.
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
De
p
t
h
,
f
t
.
95
100
105
110
115
Well Screen and Sand Filter
Drilling Method:
Drilling Company:
Drill Rig Equipment:
Other Comments:
Lo
g
:
J
M
W
Northing:
Easting:
Station:
Offset:
SOIL DESCRIPTION
20 40 60
Sa
m
p
l
e
s
6 in.
NWJ
Automatic
Refer to the report text for a proper understanding of thesubsurface materials and drilling methods. The stratificationlines indicated below represent the approximate boundariesbetween material types, and the transition may be gradual.
*
LOG OF BORING B-1
0 60
0
Total Depth:
Top Elevation:
Vert. Datum:
Horiz. Datum:
Ground Water Level ATD
Gr
o
u
n
d
Wa
t
e
r
NOTES
20 40
2.0" O.D. Split Spoon Sample
3" O.D. Thin-Walled Tube Bentonite Chips/Pellets
Bentonite Grout
Hole Diam.:
Rod Diam.:
Hammer Type:
LEGEND
Sy
m
b
o
l
Ground Water Level in Well
1. Refer to KEY for explanation of symbols, codes, abbreviations and definitions.
2. Groundwater level, if indicated above, is for the date specified and may vary.
3. USCS designation is based on visual-manual classification and selected lab testing.
Mud Rotary
Holocene Drilling
Mobile B-59
FIG. A2SHANNON & WILSON, INC.
101.5 ft.
~ 28 ft.
Sheet 4 of 4
Re
v
:
J
M
W
December 2016 21-1-22205-001
Ty
p
:
L
K
N
Geotechnical and Environmental Consultants
Sample Not Recovered
Bentonite-Cement Grout
REV 1 - Log in ProgressMA
S
T
E
R
_
L
O
G
_
E
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
4
/
1
6
PENETRATION RESISTANCE
Hammer Wt. & Drop:
(blows/foot)
140 lbs / 30 inches
Plastic Limit
Natural Water Content
% Water Content
Liquid Limit
% Fines (<0.075mm)
78
1
0.2
2.0
5.0
7.5
17.5
1
2
3
4
5
6
7
8
9
4/1
9
/
2
0
1
6
2
:
0
0
:
0
0
P
M
4/1
9
/
2
0
1
6
Asphalt.
Brown, Silty Gravel with Sand (GM); moist.
Fill (Hf)
Loose, brown, Silty Sand (SM); moist; fine
sand; nonplastic fines.
Overbank Alluvium (Ha[o])
Very loose, brown, Silt (ML); wet; few fine
sand; low plasticity fines.
Overbank Alluvium (Ha[o])
Very loose, brown, Sandy Silt (ML) to Silty
Sand (SM); wet; fine sand; nonplastic fines.
Overbank Alluvium (Ha[o])
- Gray below 15 feet.
Soft to medium stiff, gray, Elastic Silt (MH),
Organic Silt (OH), and Silt (ML); wet; trace fine
sand; medium plasticity fines, low plasticity
and nonplastic beds; few organics to some
organics in beds.
Estuarine (He)
De
p
t
h
,
f
t
.
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
De
p
t
h
,
f
t
.
5
10
15
20
25
Well Screen and Sand Filter
Drilling Method:
Drilling Company:
Drill Rig Equipment:
Other Comments:
Lo
g
:
J
M
W
Northing:
Easting:
Station:
Offset:
SOIL DESCRIPTION
20 40 60
Sa
m
p
l
e
s
6 in.
NWJ
Automatic
Refer to the report text for a proper understanding of thesubsurface materials and drilling methods. The stratificationlines indicated below represent the approximate boundariesbetween material types, and the transition may be gradual.
*
LOG OF BORING B-2
0 60
0
Total Depth:
Top Elevation:
Vert. Datum:
Horiz. Datum:
Gr
o
u
n
d
Wa
t
e
r
NOTES
CONTINUED NEXT SHEET
20 40
2.0" O.D. Split Spoon Sample
Bentonite Chips/Pellets
Bentonite Grout
Hole Diam.:
Rod Diam.:
Hammer Type:
LEGEND
Sy
m
b
o
l
Ground Water Level in VWP
Ground Water Level in Well
1. Refer to KEY for explanation of symbols, codes, abbreviations and definitions.
2. Groundwater level, if indicated above, is for the date specified and may vary.
3. USCS designation is based on visual-manual classification and selected lab testing.
Mud Rotary
Holocene Drilling
BK 81
FIG. A3SHANNON & WILSON, INC.
101.5 ft.
~ 28 ft.
Sheet 1 of 4
Re
v
:
J
M
W
December 2016 21-1-22205-001
Ty
p
:
L
K
N
Geotechnical and Environmental Consultants
Sample Not Recovered
Bentonite-Cement Grout
REV 1 - Log in ProgressMA
S
T
E
R
_
L
O
G
_
E
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
4
/
1
6
PENETRATION RESISTANCE
Hammer Wt. & Drop:
(blows/foot)
140 lbs / 30 inches
Plastic Limit
Natural Water Content
% Water Content
Liquid Limit
% Fines (<0.075mm)
WC=115
LL=70
63
31.0 10
11
12
13
14
15
Medium dense to dense, dark gray, Poorly
Graded Sand with Silt (SP-SM); wet; fine to
medium sand; trace organics.
Alluvium (Ha)
- Fine to coarse sand at 40 feet.
- Fine sand below 50 feet.
De
p
t
h
,
f
t
.
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
De
p
t
h
,
f
t
.
35
40
45
50
55
Well Screen and Sand Filter
Drilling Method:
Drilling Company:
Drill Rig Equipment:
Other Comments:
Lo
g
:
J
M
W
Northing:
Easting:
Station:
Offset:
SOIL DESCRIPTION
20 40 60
Sa
m
p
l
e
s
6 in.
NWJ
Automatic
Refer to the report text for a proper understanding of thesubsurface materials and drilling methods. The stratificationlines indicated below represent the approximate boundariesbetween material types, and the transition may be gradual.
*
LOG OF BORING B-2
0 60
0
Total Depth:
Top Elevation:
Vert. Datum:
Horiz. Datum:
Gr
o
u
n
d
Wa
t
e
r
NOTES
CONTINUED NEXT SHEET
20 40
2.0" O.D. Split Spoon Sample
Bentonite Chips/Pellets
Bentonite Grout
Hole Diam.:
Rod Diam.:
Hammer Type:
LEGEND
Sy
m
b
o
l
Ground Water Level in VWP
Ground Water Level in Well
1. Refer to KEY for explanation of symbols, codes, abbreviations and definitions.
2. Groundwater level, if indicated above, is for the date specified and may vary.
3. USCS designation is based on visual-manual classification and selected lab testing.
Mud Rotary
Holocene Drilling
BK 81
FIG. A3SHANNON & WILSON, INC.
101.5 ft.
~ 28 ft.
Sheet 2 of 4
Re
v
:
J
M
W
December 2016 21-1-22205-001
Ty
p
:
L
K
N
Geotechnical and Environmental Consultants
Sample Not Recovered
Bentonite-Cement Grout
REV 1 - Log in ProgressMA
S
T
E
R
_
L
O
G
_
E
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
4
/
1
6
PENETRATION RESISTANCE
Hammer Wt. & Drop:
(blows/foot)
140 lbs / 30 inches
Plastic Limit
Natural Water Content
% Water Content
Liquid Limit
% Fines (<0.075mm)
68.0
16
17
18
19
20
21
Medium dense, dark gray, Silty Sand (SM) to
Sandy Silt (ML); wet; fine to medium sand;
nonplastic fines; silt laminations to 3-inch-thick
silt beds, silt layer thickness increases with
depth; few organics.
Overbank Alluvium (Ha[o])
- Low plasticity beds at 80 feet.
*
De
p
t
h
,
f
t
.
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
De
p
t
h
,
f
t
.
65
70
75
80
85
Well Screen and Sand Filter
Drilling Method:
Drilling Company:
Drill Rig Equipment:
Other Comments:
Lo
g
:
J
M
W
Northing:
Easting:
Station:
Offset:
SOIL DESCRIPTION
20 40 60
Sa
m
p
l
e
s
6 in.
NWJ
Automatic
Refer to the report text for a proper understanding of thesubsurface materials and drilling methods. The stratificationlines indicated below represent the approximate boundariesbetween material types, and the transition may be gradual.
*
LOG OF BORING B-2
0 60
0
Total Depth:
Top Elevation:
Vert. Datum:
Horiz. Datum:
Gr
o
u
n
d
Wa
t
e
r
NOTES
CONTINUED NEXT SHEET
20 40
2.0" O.D. Split Spoon Sample
Bentonite Chips/Pellets
Bentonite Grout
Hole Diam.:
Rod Diam.:
Hammer Type:
LEGEND
Sy
m
b
o
l
Ground Water Level in VWP
Ground Water Level in Well
1. Refer to KEY for explanation of symbols, codes, abbreviations and definitions.
2. Groundwater level, if indicated above, is for the date specified and may vary.
3. USCS designation is based on visual-manual classification and selected lab testing.
Mud Rotary
Holocene Drilling
BK 81
FIG. A3SHANNON & WILSON, INC.
101.5 ft.
~ 28 ft.
Sheet 3 of 4
Re
v
:
J
M
W
December 2016 21-1-22205-001
Ty
p
:
L
K
N
Geotechnical and Environmental Consultants
Sample Not Recovered
Bentonite-Cement Grout
REV 1 - Log in ProgressMA
S
T
E
R
_
L
O
G
_
E
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
4
/
1
6
PENETRATION RESISTANCE
Hammer Wt. & Drop:
(blows/foot)
140 lbs / 30 inches
Plastic Limit
Natural Water Content
% Water Content
Liquid Limit
% Fines (<0.075mm)
60
93.0
98.0
101.5
22
23
24
- Low plasticity and medium plasticity beds at
90 feet.
Soft, gray-brown, Silt (ML); wet; few fine sand;
low plasticity fines.
Overbank Alluvium (Ha[o])
- Layer description based on poor sample
recovery.
Very soft, gray, Elastic Silt (MH) to Silt (ML);
wet; medium plasticity, rapid dilatancy fines.
Estuarine (He)
Note: No recovery with SPT at 100 feet, used
a 3-inch-O.D. split spoon advanced over
the same interval to collect sample.
BOTTOM OF BORING
COMPLETED 4/1/2016
De
p
t
h
,
f
t
.
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
De
p
t
h
,
f
t
.
95
100
105
110
115
Well Screen and Sand Filter
Drilling Method:
Drilling Company:
Drill Rig Equipment:
Other Comments:
Lo
g
:
J
M
W
Northing:
Easting:
Station:
Offset:
SOIL DESCRIPTION
20 40 60
Sa
m
p
l
e
s
6 in.
NWJ
Automatic
Refer to the report text for a proper understanding of thesubsurface materials and drilling methods. The stratificationlines indicated below represent the approximate boundariesbetween material types, and the transition may be gradual.
*
LOG OF BORING B-2
0 60
0
Total Depth:
Top Elevation:
Vert. Datum:
Horiz. Datum:
Gr
o
u
n
d
Wa
t
e
r
NOTES
20 40
2.0" O.D. Split Spoon Sample
Bentonite Chips/Pellets
Bentonite Grout
Hole Diam.:
Rod Diam.:
Hammer Type:
LEGEND
Sy
m
b
o
l
Ground Water Level in VWP
Ground Water Level in Well
1. Refer to KEY for explanation of symbols, codes, abbreviations and definitions.
2. Groundwater level, if indicated above, is for the date specified and may vary.
3. USCS designation is based on visual-manual classification and selected lab testing.
Mud Rotary
Holocene Drilling
BK 81
FIG. A3SHANNON & WILSON, INC.
101.5 ft.
~ 28 ft.
Sheet 4 of 4
Re
v
:
J
M
W
December 2016 21-1-22205-001
Ty
p
:
L
K
N
Geotechnical and Environmental Consultants
Sample Not Recovered
Bentonite-Cement Grout
REV 1 - Log in ProgressMA
S
T
E
R
_
L
O
G
_
E
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
4
/
1
6
PENETRATION RESISTANCE
Hammer Wt. & Drop:
(blows/foot)
140 lbs / 30 inches
Plastic Limit
Natural Water Content
% Water Content
Liquid Limit
% Fines (<0.075mm)
WOR
1
5.0
12.5
13.5
17.0
23.0
28.0
1
2
3
4
5
6
7
8
9
4/
1
9
/
2
0
1
6
2
:
0
0
:
0
0
P
M
4/
1
9
/
2
0
1
6
Medium dense, gray, Silty Sand (SM); moist;
few gravel; fine to medium sand; silt beds.
Fill (Hf)
Loose, gray-brown, Sandy Silt with Gravel
(ML); moist to wet; fine to coarse gravel and
sand; nonplastic to low plasticity fines; trace
organics.
Fill (Hf)
- Choppy drilling at 9 feet.
Loose, gray-brown to red-brown, Sandy Silt
(ML); wet; fine sand; nonplastic fines;
laminated.
Overbank Alluvium (Ha[o])
Medium stiff, gray, Elastic Silt (MH); wet; trace
fine sand; trace organics.
Estuarine (He)
Very loose to loose, dark gray, interbedded
Silty Sand (SM) and Sandy Silt (ML); wet; fine
sand; nonplastic fines; few organics, organic
odor.
Overbank Alluvium (Ha[o])
- No recovery with SPT at 20 feet. Advanced
a 3-inch O.D. split spoon over the same
interval to collect soil.
Soft, gray and brown, Organic Silt (OH); moist;
few organics, peat beds; laminated.
Estuarine (He)
Loose, dark gray, interbedded Sandy Silt (ML)
and Silty Sand (SM); wet; fine sand; nonplastic
*
De
p
t
h
,
f
t
.
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
De
p
t
h
,
f
t
.
5
10
15
20
25
Well Screen and Sand Filter
Drilling Method:
Drilling Company:
Drill Rig Equipment:
Other Comments:
Lo
g
:
J
M
W
Northing:
Easting:
Station:
Offset:
SOIL DESCRIPTION
20 40 60
Sa
m
p
l
e
s
6 in.
NWJ
Automatic
Refer to the report text for a proper understanding of thesubsurface materials and drilling methods. The stratificationlines indicated below represent the approximate boundariesbetween material types, and the transition may be gradual.
*
LOG OF BORING B-3
0 60
0
Total Depth:
Top Elevation:
Vert. Datum:
Horiz. Datum:
Gr
o
u
n
d
Wa
t
e
r
NOTES
CONTINUED NEXT SHEET
20 40
2.0" O.D. Split Spoon Sample
3" O.D. Thin-Walled Tube Bentonite Chips/Pellets
Bentonite Grout
Hole Diam.:
Rod Diam.:
Hammer Type:
LEGEND
Sy
m
b
o
l
Ground Water Level in VWP
Ground Water Level in Well
1. Refer to KEY for explanation of symbols, codes, abbreviations and definitions.
2. Groundwater level, if indicated above, is for the date specified and may vary.
3. USCS designation is based on visual-manual classification and selected lab testing.
Mud Rotary
Holocene Drilling
Mobile B-58
FIG. A4SHANNON & WILSON, INC.
141.5 ft.
~ 27.5 ft.
Sheet 1 of 5
Re
v
:
J
M
W
December 2016 21-1-22205-001
Ty
p
:
L
K
N
Geotechnical and Environmental Consultants
Sample Not Recovered
Bentonite-Cement Grout
REV 1 - Log in ProgressMA
S
T
E
R
_
L
O
G
_
E
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
4
/
1
6
PENETRATION RESISTANCE
Hammer Wt. & Drop:
(blows/foot)
140 lbs / 30 inches
Plastic Limit
Natural Water Content
% Water Content
Liquid Limit
% Fines (<0.075mm)
WC=71
35.0
10
11
12
13
14
15
and low plasticity fines; few fine to coarse
organics; elastic silt beds.
Estuarine (He)
Medium dense, dark gray, Poorly Graded
Sand with Silt (SP-SM); wet; fine to coarse
sand above 50 feet, fine sand below 50 feet.
Alluvium (Ha)
- Little organics in laminations at 55 feet.
De
p
t
h
,
f
t
.
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
De
p
t
h
,
f
t
.
35
40
45
50
55
Well Screen and Sand Filter
Drilling Method:
Drilling Company:
Drill Rig Equipment:
Other Comments:
Lo
g
:
J
M
W
Northing:
Easting:
Station:
Offset:
SOIL DESCRIPTION
20 40 60
Sa
m
p
l
e
s
6 in.
NWJ
Automatic
Refer to the report text for a proper understanding of thesubsurface materials and drilling methods. The stratificationlines indicated below represent the approximate boundariesbetween material types, and the transition may be gradual.
*
LOG OF BORING B-3
0 60
0
Total Depth:
Top Elevation:
Vert. Datum:
Horiz. Datum:
Gr
o
u
n
d
Wa
t
e
r
NOTES
CONTINUED NEXT SHEET
20 40
2.0" O.D. Split Spoon Sample
3" O.D. Thin-Walled Tube Bentonite Chips/Pellets
Bentonite Grout
Hole Diam.:
Rod Diam.:
Hammer Type:
LEGEND
Sy
m
b
o
l
Ground Water Level in VWP
Ground Water Level in Well
1. Refer to KEY for explanation of symbols, codes, abbreviations and definitions.
2. Groundwater level, if indicated above, is for the date specified and may vary.
3. USCS designation is based on visual-manual classification and selected lab testing.
Mud Rotary
Holocene Drilling
Mobile B-58
FIG. A4SHANNON & WILSON, INC.
141.5 ft.
~ 27.5 ft.
Sheet 2 of 5
Re
v
:
J
M
W
December 2016 21-1-22205-001
Ty
p
:
L
K
N
Geotechnical and Environmental Consultants
Sample Not Recovered
Bentonite-Cement Grout
REV 1 - Log in ProgressMA
S
T
E
R
_
L
O
G
_
E
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
4
/
1
6
PENETRATION RESISTANCE
Hammer Wt. & Drop:
(blows/foot)
140 lbs / 30 inches
Plastic Limit
Natural Water Content
% Water Content
Liquid Limit
% Fines (<0.075mm)
83.0
16
17
18
19
20
21
- Gray laminations at 75 feet.
Very soft to medium stiff, gray-brown, Lean
Clay (CL) and Silt (ML); wet; trace to few fine
sand; medium plasticity fines; trace to little
organics, mostly organics in beds; trace shells.
Estuarine (He)
*
De
p
t
h
,
f
t
.
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
De
p
t
h
,
f
t
.
65
70
75
80
85
Well Screen and Sand Filter
Drilling Method:
Drilling Company:
Drill Rig Equipment:
Other Comments:
Lo
g
:
J
M
W
Northing:
Easting:
Station:
Offset:
SOIL DESCRIPTION
20 40 60
Sa
m
p
l
e
s
6 in.
NWJ
Automatic
Refer to the report text for a proper understanding of thesubsurface materials and drilling methods. The stratificationlines indicated below represent the approximate boundariesbetween material types, and the transition may be gradual.
*
LOG OF BORING B-3
0 60
0
Total Depth:
Top Elevation:
Vert. Datum:
Horiz. Datum:
Gr
o
u
n
d
Wa
t
e
r
NOTES
CONTINUED NEXT SHEET
20 40
2.0" O.D. Split Spoon Sample
3" O.D. Thin-Walled Tube Bentonite Chips/Pellets
Bentonite Grout
Hole Diam.:
Rod Diam.:
Hammer Type:
LEGEND
Sy
m
b
o
l
Ground Water Level in VWP
Ground Water Level in Well
1. Refer to KEY for explanation of symbols, codes, abbreviations and definitions.
2. Groundwater level, if indicated above, is for the date specified and may vary.
3. USCS designation is based on visual-manual classification and selected lab testing.
Mud Rotary
Holocene Drilling
Mobile B-58
FIG. A4SHANNON & WILSON, INC.
141.5 ft.
~ 27.5 ft.
Sheet 3 of 5
Re
v
:
J
M
W
December 2016 21-1-22205-001
Ty
p
:
L
K
N
Geotechnical and Environmental Consultants
Sample Not Recovered
Bentonite-Cement Grout
REV 1 - Log in ProgressMA
S
T
E
R
_
L
O
G
_
E
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
4
/
1
6
PENETRATION RESISTANCE
Hammer Wt. & Drop:
(blows/foot)
140 lbs / 30 inches
Plastic Limit
Natural Water Content
% Water Content
Liquid Limit
% Fines (<0.075mm)
103.0
112.0
22
23
24
25
26
27
28
Medium dense, gray, Silt (ML); wet; trace fine
sand; nonplastic fines; trace to some organics.
Estuarine (He)
- Medium plasticity beds at 110 feet.
Medium dense to dense, gray, Poorly Graded
Gravel with Sand (GP); wet; possible cobbles
based on drill action; interbedded with silt or
sand based on drill action; significant mud
loss.
Alluvium (Ha)
- Lost drilling fluid starting at 112 feet.
*
De
p
t
h
,
f
t
.
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
De
p
t
h
,
f
t
.
95
100
105
110
115
Well Screen and Sand Filter
Drilling Method:
Drilling Company:
Drill Rig Equipment:
Other Comments:
Lo
g
:
J
M
W
Northing:
Easting:
Station:
Offset:
SOIL DESCRIPTION
20 40 60
Sa
m
p
l
e
s
6 in.
NWJ
Automatic
Refer to the report text for a proper understanding of thesubsurface materials and drilling methods. The stratificationlines indicated below represent the approximate boundariesbetween material types, and the transition may be gradual.
*
LOG OF BORING B-3
0 60
0
Total Depth:
Top Elevation:
Vert. Datum:
Horiz. Datum:
Gr
o
u
n
d
Wa
t
e
r
NOTES
CONTINUED NEXT SHEET
20 40
2.0" O.D. Split Spoon Sample
3" O.D. Thin-Walled Tube Bentonite Chips/Pellets
Bentonite Grout
Hole Diam.:
Rod Diam.:
Hammer Type:
LEGEND
Sy
m
b
o
l
Ground Water Level in VWP
Ground Water Level in Well
1. Refer to KEY for explanation of symbols, codes, abbreviations and definitions.
2. Groundwater level, if indicated above, is for the date specified and may vary.
3. USCS designation is based on visual-manual classification and selected lab testing.
Mud Rotary
Holocene Drilling
Mobile B-58
FIG. A4SHANNON & WILSON, INC.
141.5 ft.
~ 27.5 ft.
Sheet 4 of 5
Re
v
:
J
M
W
December 2016 21-1-22205-001
Ty
p
:
L
K
N
Geotechnical and Environmental Consultants
Sample Not Recovered
Bentonite-Cement Grout
REV 1 - Log in ProgressMA
S
T
E
R
_
L
O
G
_
E
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
4
/
1
6
PENETRATION RESISTANCE
Hammer Wt. & Drop:
(blows/foot)
140 lbs / 30 inches
Plastic Limit
Natural Water Content
% Water Content
Liquid Limit
% Fines (<0.075mm)
NP
WOR
WOR
50/5"
130.0
133.0
141.5
29
30
31
32
33
- Poor sample recovery in this layer.
Dense, gray, Silty Sand (SM); wet; fine to
medium sand.
Alluvium (Ha)
Dense, gray, Poorly Graded Gravel with Silt
and Sand (GP-GM); wet; fine to coarse gravel;
could not maintain mud circulation below 140
feet.
Alluvium (Ha)
BOTTOM OF BORING
COMPLETED 3/30/2016
*
De
p
t
h
,
f
t
.
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
De
p
t
h
,
f
t
.
125
130
135
140
145
Well Screen and Sand Filter
Drilling Method:
Drilling Company:
Drill Rig Equipment:
Other Comments:
Lo
g
:
J
M
W
Northing:
Easting:
Station:
Offset:
SOIL DESCRIPTION
20 40 60
Sa
m
p
l
e
s
6 in.
NWJ
Automatic
Refer to the report text for a proper understanding of thesubsurface materials and drilling methods. The stratificationlines indicated below represent the approximate boundariesbetween material types, and the transition may be gradual.
*
LOG OF BORING B-3
0 60
0
Total Depth:
Top Elevation:
Vert. Datum:
Horiz. Datum:
Gr
o
u
n
d
Wa
t
e
r
NOTES
20 40
2.0" O.D. Split Spoon Sample
3" O.D. Thin-Walled Tube Bentonite Chips/Pellets
Bentonite Grout
Hole Diam.:
Rod Diam.:
Hammer Type:
LEGEND
Sy
m
b
o
l
Ground Water Level in VWP
Ground Water Level in Well
1. Refer to KEY for explanation of symbols, codes, abbreviations and definitions.
2. Groundwater level, if indicated above, is for the date specified and may vary.
3. USCS designation is based on visual-manual classification and selected lab testing.
Mud Rotary
Holocene Drilling
Mobile B-58
FIG. A4SHANNON & WILSON, INC.
141.5 ft.
~ 27.5 ft.
Sheet 5 of 5
Re
v
:
J
M
W
December 2016 21-1-22205-001
Ty
p
:
L
K
N
Geotechnical and Environmental Consultants
Sample Not Recovered
Bentonite-Cement Grout
REV 1 - Log in ProgressMA
S
T
E
R
_
L
O
G
_
E
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
4
/
1
6
PENETRATION RESISTANCE
Hammer Wt. & Drop:
(blows/foot)
140 lbs / 30 inches
Plastic Limit
Natural Water Content
% Water Content
Liquid Limit
% Fines (<0.075mm)
50/5"
67
St
r
a
n
d
e
r
‐
GW
& SW
Da
t
a
‐
11
‐04
‐16
11
/
1
5
/
2
0
1
6
FIG. A-5
3.
G
r
o
u
n
d
w
a
t
e
r
e
l
e
v
a
t
i
o
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p
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De
c
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mb
e
r
2
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1
6
21-1-22205-001
4.
B
-
3
-
v
w
p
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a
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h
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e
p
t
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b
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7
,
2
0
1
6
.
FIG. A-5
2.
G
r
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=
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S
1
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3
5
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R
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STAGE DATA
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S
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r
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1
5
m
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SH
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&
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.
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8910111213141516171819202122
A
p
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8
8
(
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)
B ‐1 ‐ow
B ‐2 ‐ow
B ‐2 ‐vw
p
B ‐3 ‐ow
B ‐3 ‐vw
p
Green River
<e
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.
17
ft
fr
o
m
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l
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3
to
Oc
t
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17 DRAFT
St
r
a
n
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‐
GW
& SW
Da
t
a
‐
11
‐04
‐16
11
/
1
5
/
2
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FIG. A-6
3.
P
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21-1-22205-001 FIG. A-6
2.
G
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0.00.51.01.52.0
24
.
0
25
.
0
26
.
0
27
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0
28
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0
Preciptiaiton (inches)
A
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l
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=
o
b
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d
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c
t
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m
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n
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s
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t
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d
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l
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n
p
l
o
t
i
s
s
e
l
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d
b
a
s
e
d
o
n
B
o
u
w
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r
a
n
d
R
i
c
e
(
1
9
7
6
)
.
EXH. A-7a
De
c
em
b
e
r
2
0
1
6
21-1-22205-001 EXHIBIT A-7a
ft
=
f
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t
2.
A
q
u
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f
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m
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l
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.
1.
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A
N
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I
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I
N
C
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t
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c
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1
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2
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3
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4
0.
5
0.
0
1
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11.
10
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Ti
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e
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D
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6
EXH. A-7b
De
c
em
b
e
r
2
0
1
6
21-1-22205-001 EXHIBIT A-7b
St
r
a
n
d
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r
B
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v
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E
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=
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2.
A
q
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=
o
b
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d
l
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t
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s
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b
a
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d
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w
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c
e
(
1
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)
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c
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s
SH
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1
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2
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3
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4
0.
5
0.
0
1
0.
11.
10
.
Ti
m
e
(mi
n
)
D
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s
p
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t
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f
t
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s
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W
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l
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s
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1
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1
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2
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0
1
3
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1
S
l
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2
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6
EXH. A-7c
De
c
em
b
e
r
2
0
1
6
21-1-22205-001 EXHIBIT A-7c
St
r
a
n
d
e
r
B
o
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v
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E
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3
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l
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m
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a
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D
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c
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Ci
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B
-
1
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G
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A
D
T
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3
NO
T
E
S
1.
S
l
u
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t
e
s
t
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n
a
l
y
s
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p
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m
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d
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A
Q
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®
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s
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4
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5
.
cm
=
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t
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r
s
ft
=
f
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t
2.
A
q
u
i
f
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r
m
o
d
e
l
r
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f
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s
t
o
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f
a
q
u
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f
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(
c
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n
f
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d
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n
c
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n
f
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d
)
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d
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l
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l
y
s
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s
.
mi
n
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m
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p
t
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f
m
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d
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l
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d
l
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3.
O
b
s
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r
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d
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t
d
a
t
a
r
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p
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b
y
s
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u
a
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s
i
n
p
l
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t
.
K
=
h
y
d
r
a
u
l
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c
c
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d
u
c
t
i
v
i
t
y
ob
s
.
=
o
b
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r
v
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t
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n
4.
M
o
d
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l
e
d
l
i
n
e
i
n
p
l
o
t
i
s
s
e
l
e
c
t
e
d
b
a
s
e
d
o
n
B
o
u
w
e
r
a
n
d
R
i
c
e
(
1
9
7
6
)
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se
c
=
s
e
c
o
n
d
s
SH
A
N
N
O
N
&
W
I
L
S
O
N
,
I
N
C
.
Ge
o
t
e
c
h
n
i
c
a
l
a
n
d
E
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v
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m
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t
a
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C
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s
u
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t
a
n
t
s
0.
0.
1
0.
2
0.
3
0.
4
0.
5
0.
0
1
0.
11.
10
.
Ti
m
e
(mi
n
)
D
i
s
p
l
a
c
e
m
e
n
t
(
f
t
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O
b
s
.
W
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l
l
s
B-
1
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u
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f
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r
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Co
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f
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d
So
l
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Bo
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-
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c
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r
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m
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K
=
0
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0
0
8
4
2
3
c
m
/se c
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=
1
.
2
9
f
t
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B-
1
S
l
u
g
T
e
s
t
F
i
g
u
r
e
s
1
1
/
1
5
/
2
0
1
6
EXH. A-7d
NO
T
E
S
1.
S
l
u
g
t
e
s
t
a
n
a
l
y
s
i
s
p
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r
f
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m
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d
u
s
i
n
g
A
Q
T
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S
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L
V
®
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e
r
s
i
o
n
4
.
5
.
3.
O
b
s
e
r
v
e
d
t
e
s
t
d
a
t
a
r
e
p
r
e
s
e
n
t
e
d
b
y
s
q
u
a
r
e
s
i
n
p
l
o
t
.
EXHIBIT A-7d
St
r
a
n
d
e
r
B
o
u
l
e
v
a
r
d
E
x
t
e
n
s
i
o
n
P
h
a
s
e
3
Pr
e
l
i
m
i
n
a
r
y
D
e
s
i
g
n
-
G
e
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t
e
c
h
n
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c
a
l
Ci
t
y
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T
u
k
w
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l
a
,
W
a
s
h
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n
g
t
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n
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U
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S
T
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S
U
L
T
S
B
-
1
RI
S
I
N
G
H
E
A
D
T
E
S
T
1
De
c
em
b
e
r
2
0
1
6
21-1-22205-001
cm
=
c
e
n
t
i
m
e
t
e
r
s
ft
=
f
e
e
t
2.
A
q
u
i
f
e
r
m
o
d
e
l
r
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f
e
r
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s
t
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y
p
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f
a
q
u
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f
e
r
(
c
o
n
f
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n
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d
o
r
u
n
c
o
n
f
i
n
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d
)
u
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d
f
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s
l
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s
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s
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s
.
mi
n
=
m
i
n
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t
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s
y 0 =y
-
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p
t
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f
m
o
d
e
l
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d
l
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n
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K
=
h
y
d
r
a
u
l
i
c
c
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n
d
u
c
t
i
v
i
t
y
ob
s
.
=
o
b
s
e
r
v
a
t
i
o
n
4.
M
o
d
e
l
e
d
l
i
n
e
i
n
p
l
o
t
i
s
s
e
l
e
c
t
e
d
b
a
s
e
d
o
n
B
o
u
w
e
r
a
n
d
R
i
c
e
(
1
9
7
6
)
.
se
c
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6
21-1-22205-001 EXHIBIT A-9a
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De
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2
0
1
6
21-1-22205-001 EXHIBIT A-9b
St
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EXH. A-9c
De
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2
0
1
6
21-1-22205-001 EXHIBIT A-9c
St
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2
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6
21-1-22205-001
EXH. A-9d
NO
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S
1.
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p
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d
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A
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5
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3.
O
b
s
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r
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e
d
t
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s
t
d
a
t
a
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t
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d
b
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q
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p
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.
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DRAFT
Shannon & Wilson
Operator: Romanelli
Sounding: CPT-01
Cone Used: DDG1368
GPS Data: NO GPS
CPT Date/Time: 5/26/2016 9:04:35 AM
Location: Tukwila/Renton
Job Number: 21-1-22205-900
Maximum Depth = 80.22 feet Depth Increment = 0.164 feet
*Soil behavior type and SPT based on data from UBC-1983
Tip Resistance
Qt TSF
3000
0
10
20
30
40
50
60
70
80
Depth
(ft)
Pore Pressure
Pw PSI
45-5
Friction Ratio
Fs/Qt (%)
50
Soil Behavior Type*
Zone: UBC-1983
1 sensitive fine grained
2 organic material
3 clay
4 silty clay to clay
5 clayey silt to silty clay
6 sandy silt to clayey silt
7 silty sand to sandy silt
8 sand to silty sand
9 sand
10 gravelly sand to sand
11 very stiff fine grained (*)
12 sand to clayey sand (*)
120
SPT N*
60% Hammer
600
DRAFT
Shannon & Wilson
Operator: Romanelli
Sounding: CPT-02
Cone Used: DDG1368
GPS Data: NO GPS
CPT Date/Time: 5/26/2016 12:26:06 PM
Location: Tukwila/Renton
Job Number: 21-1-22205-900
Maximum Depth = 80.22 feet Depth Increment = 0.164 feet
*Soil behavior type and SPT based on data from UBC-1983
Tip Resistance
Qt TSF
3000
0
10
20
30
40
50
60
70
80
Depth
(ft)
Pore Pressure
Pw PSI
45-5
Friction Ratio
Fs/Qt (%)
50
Soil Behavior Type*
Zone: UBC-1983
1 sensitive fine grained
2 organic material
3 clay
4 silty clay to clay
5 clayey silt to silty clay
6 sandy silt to clayey silt
7 silty sand to sandy silt
8 sand to silty sand
9 sand
10 gravelly sand to sand
11 very stiff fine grained (*)
12 sand to clayey sand (*)
120
SPT N*
60% Hammer
600
DRAFT
Shannon & Wilson
Operator: Romanelli
Sounding: CPT-03
Cone Used: DDG1368
GPS Data: NO GPS
CPT Date/Time: 5/26/2016 11:29:13 AM
Location: Tukwila/Renton
Job Number: 21-1-22205-900
Maximum Depth = 80.22 feet Depth Increment = 0.164 feet
*Soil behavior type and SPT based on data from UBC-1983
Tip Resistance
Qt TSF
3000
0
10
20
30
40
50
60
70
80
Depth
(ft)
Pore Pressure
Pw PSI
45-5
Friction Ratio
Fs/Qt (%)
50
Soil Behavior Type*
Zone: UBC-1983
1 sensitive fine grained
2 organic material
3 clay
4 silty clay to clay
5 clayey silt to silty clay
6 sandy silt to clayey silt
7 silty sand to sandy silt
8 sand to silty sand
9 sand
10 gravelly sand to sand
11 very stiff fine grained (*)
12 sand to clayey sand (*)
120
SPT N*
60% Hammer
600
DRAFT
Pressure
(psi)
Time: (seconds)
Shannon & Wilson
Operator Romanelli
Sounding: CPT-04
Cone Used: DDG1368
GPS Data: NO GPS
CPT Date/Time: 5/26/2016 1:25:35 PM
Location: Tukwila/Renton
Job Number: 21-1-22205-900
Maximum Pressure = 0.68 psi
1 10 100 1000 10000
-1
0
1
Selected Depth(s)
(feet)
14.928
DRAFT
Pressure
(psi)
Time: (seconds)
Shannon & Wilson
Operator Romanelli
Sounding: CPT-04
Cone Used: DDG1368
GPS Data: NO GPS
CPT Date/Time: 5/26/2016 1:25:35 PM
Location: Tukwila/Renton
Job Number: 21-1-22205-900
Maximum Pressure = 36.463 psi
1 10 100 1000 10000
10
15
20
25
30
35
40
Selected Depth(s)
(feet)
24.934
DRAFT
Shannon & Wilson
Operator: Romanelli
Sounding: CPT-04
Cone Used: DDG1368
GPS Data: NO GPS
CPT Date/Time: 5/26/2016 1:25:35 PM
Location: Tukwila/Renton
Job Number: 21-1-22205-900
Maximum Depth = 80.22 feet Depth Increment = 0.164 feet
*Soil behavior type and SPT based on data from UBC-1983
Tip Resistance
Qt TSF
3000
0
10
20
30
40
50
60
70
80
Depth
(ft)
Pore Pressure
Pw PSI
45-5
Friction Ratio
Fs/Qt (%)
50
Soil Behavior Type*
Zone: UBC-1983
1 sensitive fine grained
2 organic material
3 clay
4 silty clay to clay
5 clayey silt to silty clay
6 sandy silt to clayey silt
7 silty sand to sandy silt
8 sand to silty sand
9 sand
10 gravelly sand to sand
11 very stiff fine grained (*)
12 sand to clayey sand (*)
120
SPT N*
60% Hammer
600
DRAFT
Shannon & Wilson
Operator: Romanelli
Sounding: CPT-05
Cone Used: DDG1368
GPS Data: NO GPS
CPT Date/Time: 5/26/2016 4:22:20 PM
Location: Tukwila/Renton
Job Number: 21-1-22205-900
Maximum Depth = 80.22 feet Depth Increment = 0.164 feet
*Soil behavior type and SPT based on data from UBC-1983
Tip Resistance
Qt TSF
3000
0
10
20
30
40
50
60
70
80
Depth
(ft)
Pore Pressure
Pw PSI
45-5
Friction Ratio
Fs/Qt (%)
50
Soil Behavior Type*
Zone: UBC-1983
1 sensitive fine grained
2 organic material
3 clay
4 silty clay to clay
5 clayey silt to silty clay
6 sandy silt to clayey silt
7 silty sand to sandy silt
8 sand to silty sand
9 sand
10 gravelly sand to sand
11 very stiff fine grained (*)
12 sand to clayey sand (*)
120
SPT N*
60% Hammer
600
DRAFT
21-1-22205-001
APPENDIX B
GEOTECHNICAL LABORATORY TESTING
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21-1-22205-001-R1-AB 21-1-22205-001 B-i
APPENDIX B GEOTECHNICAL LABORATORY TESTING
TABLE OF CONTENTS Page
B.1 VISUAL CLASSIFICATION .........................................................................................B-1
B.2 WATER CONTENT DETERMINATION ......................................................................B-1
B.3 GRAIN SIZE DISTRIBUTION ANALYSIS ..................................................................B-1 B.3.1 Sieve Analysis ...................................................................................................B-2
B.3.2 Fines Content Determination .............................................................................B-2
B.3.3 Combined Analysis ...........................................................................................B-2
B.4 SPECIFIC GRAVITY DETERMINATION ...................................................................B-2
B.5 ATTERBERG LIMITS DETERMINATION..................................................................B-2
B.6 CONSIDERATIONS .......................................................................................................B-3
B.7 REFERENCES ................................................................................................................B-3
TABLES
Laboratory Terms
Sample Types
Laboratory Test Summary
TESTS
Grain Size Distribution Plot, Boring B-1
Grain Size Distribution Plot, Boring B-2
Grain Size Distribution Plot, Boring B-3
Plasticity Chart, Boring B-1 Plasticity Chart, Boring B-2
Plasticity Chart, Boring B-3
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21-1-22205-001-R1-AB 21-1-22205-001 B-1
APPENDIX B GEOTECHNICAL LABORATORY TESTING
We performed geotechnical laboratory testing on selected soil samples retrieved from the three
borings completed for the Strander Boulevard Extension Phase 3 Project Preliminary Design -
Geotechnical Project. The laboratory testing program included tests to classify the soil and
provide data for engineering studies. We performed visual classification on all retrieved samples.
Our laboratory testing program included water content determinations, grain size distribution
analyses, specific gravity determinations, and Atterberg limits determinations.
The following sections describe the laboratory test procedures.
B.1 VISUAL CLASSIFICATION
We visually classified soil samples retrieved from the borings using a system based on ASTM
International (ASTM) D2487-11, Standard Test Method for Classification of Soil for
Engineering Purposes, and ASTM D2488-09a, Standard Recommended Practice for Description
of Soils (Visual-Manual Procedure). We summarize our classification system in Appendix A.
We assigned a Unified Soil Classification System (USCS) group name and symbol, based on our
visual classification of particles finer than 76.2 millimeters (3 inches). We revised visual
classifications using results of the index tests discussed below.
B.2 WATER CONTENT DETERMINATION
We tested the water content of selected samples in accordance with ASTM D2216-10, Standard
Method for Laboratory Determination of Water (Moisture) Content of Soil, Rock, and Soil-
Aggregate Mixtures. Comparison of the water content of a soil with its index properties can be
useful in characterizing soil unit weight, consistency, compressibility, and strength. We present
water content test results in the Laboratory Test Summary table in this appendix, and graphically
on boring logs in Appendix A.
B.3 GRAIN SIZE DISTRIBUTION ANALYSIS
Grain size distribution analyses separate soil particles through mechanical or sedimentation
processes. Grain size distributions are used to classify the granular component of soils and can
correlate with soil properties, including frost susceptibility, permeability, shear strength,
liquefaction potential, capillary action, and sensitivity to moisture. We plot grain size
distribution analysis results in this appendix. Grain size distribution plots provide tabular
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21-1-22205-001-R1-AB 21-1-22205-001 B-2
information about each specimen, including: USCS group symbol and group name; water
content; constituent (i.e., cobble, gravel, sand, and fines) percentages; coefficients of uniformity
and curvature, if applicable; personnel initials; ASTM standard designation; and testing remarks.
Constituent percentages are presented in the Lab Summary Table in this appendix and fines
contents are plotted as data points on borings logs in Appendix A.
B.3.1 Sieve Analysis
We performed mechanical sieve analyses on selected soil specimens to determine the
grain size distribution of coarse-grained soil particles, in accordance with ASTM C136/C136M-
14, Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates.
B.3.2 Fines Content Determination
We determined the percent of fine-grained soil particles (fines content) of selected soil
specimens, in accordance with ASTM D1140-14, Standard Test Methods for Determining the
Amount of Material Finer Than 0.075 mm (No. 200) Sieve in Soils by Washing.
B.3.3 Combined Analysis
We performed combined analyses (mechanical and sedimentation) on selected soil
specimens to determine the grain size distribution of coarse- and fine-grained soil particles, in
accordance with ASTM D422-63 (2007)e2, Standard Test Method for Particle-Size Analysis of
Soils. We assumed a specific gravity of 2.7 for hydrometer calculations, unless otherwise
indicated on grain size distribution plots.
B.4 SPECIFIC GRAVITY DETERMINATION
We determined the specific gravity of selected samples in accordance with ASTM D854-14,
Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer, Method A. We
present specific gravity test results in the Lab Summary Table in this appendix.
B.5 ATTERBERG LIMITS DETERMINATION
We determined soil plasticity by performing Atterberg Limits tests on selected samples in
accordance with ASTM D4318-10e1, Standard Test Method for Liquid Limit, Plastic Limit, and
Plasticity Index of Soils, Method A (Multi-Point Liquid Limit). The Atterberg Limits include
liquid limit (LL), plastic limit (PL), and plasticity index (PI=LL-PL). These limits can assist soil
classification, indicate soil consistency (when compared to natural water content), provide
correlation to soil properties, evaluate clogging potential, and estimate liquefaction potential.
DR
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21-1-22205-001-R1-AB 21-1-22205-001 B-3
We present soil plasticity test results in the Lab Summary Table and on plasticity charts in this
appendix. Plasticity charts provide the liquid limit, plastic limit, plasticity index, USCS group
symbol, the sample description, water content, and percent passing the No. 200 sieve (if a grain
size distribution analysis was performed). Soil plasticity test results are also shown graphically
on the exploration logs presented in Appendix A.
B.6 CONSIDERATIONS
Drilling and sampling methodologies may affect the outcome of prescribed geotechnical
laboratory tests. Refer to the field exploration discussion in this report for a discussion of these
potential effects. Instances of limited recovery may have resulted in test samples not meeting
specified minimum mass requirements, per ASTM standards. Test plots show which samples do
not meet ASTM specified minimum mass requirements.
B.7 REFERENCES
ASTM International, 2011, Standard practice for classification of soils for engineering purposes
(unified soil classification system), D2487-11: West Conshohocken, Pa., ASTM International, Annual book of standards, v. 04.08, soil and rock (I): D420 - D5876, 12 p.,
available: www.astm.org.
ASTM International, 2010, Standard test methods for laboratory determination of water
(moisture) content of soil and rock by mass, D2216-10: West Conshohocken, Pa., ASTM International, Annual book of standards, v. 04.08, soil and rock (I): D420 - D5876, 7 p.,
available: www.astm.org.
ASTM International, 2014, Standard test method for sieve analysis of fine and coarse aggregates,
C136-14: West Conshohocken, Pa., ASTM International, Annual book of standards, v. 04.02, concrete and aggregates, 5 p., available: www.astm.org.
ASTM International, 2014, Standard test methods for determining the amount of material finer
than .075mm (no. 200) sieve in soils by washing, D1140-14: West Conshohocken, Pa.,
ASTM International, Annual book of standards, v. 04.08, soil and rock (I): D420 - D5876, 6 p., available: www.astm.org.
ASTM International, 2007, Standard test method for particle-size analysis of soils, D422-
63(2007)e2: West Conshohocken, Pa., ASTM International, Annual book of standards, v.
04.08, soil and rock (I): D420 - D5876, 8 p., available: www.astm.org.
ASTM International, 2014, Standard test methods for specific gravity of soil solids by water
pycnometer, D854-14: West Conshohocken, Pa., ASTM International, Annual book of
standards, v. 04.08, soil and rock (I): D420 - D5876, 8 p., available: www.astm.org.
DR
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21-1-22205-001-R1-AB 21-1-22205-001 B-4
ASTM International, 2010, Standard test methods for liquid limit, plastic limit, and plasticity index of soils, D4318-10e1: West Conshohocken, Pa., ASTM International, Annual book of
standards, v. 04.08, soil and rock (I): D420 - D5876, 16 p., available: www.astm.org.
DR
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LABORATORY TERMS
Abbreviations,
Symbols, and Terms Descriptions
%Percent
*Sample specimen weight did not meet required minimum mass for the test method
ASTM Std.ASTM International Standard
Cc Coefficient of curvature
Clay-size Soil particles finer than 0.002 mm
cm Centimeter
cm2 Square centimeter
Coarse-grained Soil particles coarser than 0.075 mm (cobble-, gravel- and sand-sized particles)
Cobbles Soil particles finer than 305 mm and coarser than 76.2 mm
Cu Coefficient of uniformity
CU Consolidated Undrained
e Axial strain
Fine-grained Soil particles finer than 0.075 mm (silt- and clay-sized particles)
ft Feet
gm Wet unit weight
Gravel Soil particles finer than 76.2 mm and coarser than 4.75 mm
Gs Specific gravity of soil solids
Ho Initial height
DH Change in height
DHload End of load increment deformation
in Inch
in3 Cubic inch
LL Liquid Limit
min Minute
mm Millimeter
mm Micrometer
MPa Mega-Pascal
NP Non-plastic
OC Organic content
p Total stress
p'Effective stress
Pa Pascal
pcf Pounds per cubic foot
PI Plasticity Index
PL Plastic Limit
psf Pounds per square foot
q Deviatoric stress
Sand Soil particles finer than 4.75 mm and coarser than 0.075 mm
sec Second
Silt Soil particles finer than 0.075 mm and coarser than 0.002 mm
tn Time to n% primary consolidation
tload Duration of load increment
tsf Short tons per square foot
USCS Unified Soil Classification System
UU Unconsolidated-Undrained
WC Water content
21-1-22205-001-R1-AB-Table 21-1-22205-001
DR
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SAMPLE TYPES
Abbreviations,
Symbols, and Terms Descriptions
2SS 2.5" O.D. Split Spoon Sample
2ST 2" O.D. Thin-Walled Tube
3HSA 3" CME HSA Sampler
3SS 3" O.D. Split Spoon Sample
4SS 4" I.D. Split Spoon Sample
6SS 6" I.D. Split Spoon Sample
CA_MC Modified California Sampler
CA_SPT Standard Penetration Test (SPT)
CORE Rock Core
DM + 3.25" O.D. Split Spoon Sample
DMR 3.25" Sampler With Internal Rings
GRAB Grab Sample
GUS 3.0" O.D. GUS Sample
OSTER 3.0" O.D. Osterberg Sample
PITCHER 3" O.D. Pitcher Sample
PMT Pressuremeter Test (f=failed)
PO Porter Penetration Test Sample
PT 2.5" O.D. Thin-Walled Tube
ROCK Rock Core Sample
SCORE Soil Core (as in Sonic Core Borings)
SH1 1" Plastic Sheath
SH2 2" Plastic Sheath with Soil Recovery
SH3 2" Plastic Sheath with no Soil Recovery
SPT 2.0" O.D. Split Spoon Sample
SS Split Spoon
ST 3" O.D. Thin-Walled Tube
STW 3" O.D. Thin-Walled Tube
TEST Sample Test Interval
TR TR Test
TW Thin Wall Sample
UNDIST Undisturbed Sample
VANE Vane Shear
WATER Water sample for Probe Logs
XCORE Core Sample
21-1-22205-001-R1-AB-Table 21-1-22205-001
DR
A
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LABORATORY TEST SUMMARY
Boring To
p
D
e
p
t
h
(
f
t
)
Sa
m
p
l
e
N
u
m
b
e
r
Sa
m
p
l
e
T
y
p
e
Bl
o
w
C
o
u
n
t
USCS WC (%)%
G
r
a
v
e
l
%
S
a
n
d
%
F
i
n
e
s
%
C
l
a
y
-
s
i
z
e
Cu Cc Gs LL PL NP Soil Description
B-1 2.5 S-1 SPT 8 20.8
B-1 5 S-2 SPT 3 23.2
B-1 7.5 S-3 SPT 4 34.4
B-1 10 S-4 SPT 3 SM 39.1 0 55 44 5 2.70 Silty Sand
B-1 12.5 S-5 SPT 3 50.0
B-1 17.5 S-7 SPT 2 ML 71.3 2*39*58*6*Sandy Silt
B-1 20 S-8 SPT 5 35.1
B-1 25 S-9 SPT 3 OH 76.3 86 52 Organic Silt
B-1 30 S-10 SPT 4 OH 60.0 9 91 20 2.55 Organic Silt
B-1 35 S-12 SPT 3 32.9
B-1 40 S-13 SPT 30 23.6
B-1 45 S-14 SPT 31 SP-SM 24.1 94*6*2.8 1.2 Poorly Graded Sand with Silt
B-1 50 S-15 SPT 29 28.3
B-1 55 S-16 SPT 36 SP-SM 25.0 92*7.8*Poorly Graded Sand with Silt
B-1 60 S-17 SPT 32 26.6
B-1 65 S-18 SPT 30 SM 29.6 87*13*Silty Sand
B-1 70 S-19 SPT 33 28.2
B-1 80 S-21 SPT 20 36.3
B-1 85 S-22 SPT 18 ML 35.5 0*43*57*Sandy Silt
B-1 90 S-23 SPT 7 41.6
B-1 95 S-24 SPT 6 ML 31.1 22 78 11 2.67 Silt with Sand
B-1 100 S-25 SPT 2 ML 42.4 37 27 Silt
B-2 3 S-1 SPT 5 23.2
B-2 5 S-2 SPT 2 ML 41.9 30 29 Silt
B-2 7.5 S-3 SPT 1 ML 41.0 37 63 5 Sandy Silt
B-2 10 S-4 SPT 1 45.1
B-2 12.5 S-5 SPT 1 SM 41.0 53 47 4 2.70 Silty Sand
B-2 15 S-6 SPT 1 47.4
B-2 17.5 S-7 SPT 3 MH 44.4 70 39 Elastic Silt
B-2 20 S-8 SPT 6 43.9
B-2 25 S-9 SPT 2 114.6
B-2 30 S-10 SPT 15 35.4
21-1-22205-00121-1-22205-001-R1-AB-Table
DR
A
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LABORATORY TEST SUMMARY
Boring To
p
D
e
p
t
h
(
f
t
)
Sa
m
p
l
e
N
u
m
b
e
r
Sa
m
p
l
e
T
y
p
e
Bl
o
w
C
o
u
n
t
USCS WC (%)%
G
r
a
v
e
l
%
S
a
n
d
%
F
i
n
e
s
%
C
l
a
y
-
s
i
z
e
Cu Cc Gs LL PL NP Soil Description
B-2 31 S-10 SPT 15 26.6
B-2 35 S-11 SPT 17 32.0
B-2 40 S-12 SPT 25 SP-SM 23.4 0*94*5.5*2.9 1.4 Poorly Graded Sand with Silt
B-2 45 S-13 SPT 25 24.4
B-2 50 S-14 SPT 30 SP-SM 25.3 94*6.1*Poorly Graded Sand with Silt
B-2 55 S-15 SPT 30 26.1
B-2 60 S-16 SPT 30 SP-SM 27.7 93*6.9*2.7 3.8 Poorly Graded Sand with Silt
B-2 65 S-17 SPT 23 37.0
B-2 75 S-19 SPT 19 38.6
B-2 80 S-20 SPT 16 33.4
B-2 85 S-21 SPT 15 ML 35.4 40 60 9 2.67 Sandy Silt
B-2 90 S-22 SPT 12 33.9
B-2 100 S-24 SPT 0 38.2
B-3 2.5 S-1 SPT 13 16.0
B-3 5 S-2 SPT 10 22.3
B-3 7.5 S-3 SPT 10 19.9
B-3 10 S-4 SPT 5 19.9
B-3 12.5 S-5 SPT 7 28.1
B-3 13.5 S-5B SPT 7 MH 34.2 55 30 Elastic Silt
B-3 17.5 S-7 SPT 5 32.9
B-3 20 S-8 SPT 3 SM 46.5 3*55*42*5*Silty Sand
B-3 25 S-9 SPT 2 71.1
B-3 30 S-10 SPT 7 33.5
B-3 35 S-11 SPT 24 21.3
B-3 40 S-12 SPT 23 SP-SM 23.0 0 93 6.4 3.4 1.8 Poorly Graded Sand with Silt
B-3 45 S-13 SPT 23 20.0
B-3 50 S-14 SPT 29 SP-SM 26.1 95 5.1 2.6 1.2 Poorly Graded Sand with Silt
B-3 55 S-15 SPT 26 29.2
B-3 60 S-16 SPT 26 29.5
B-3 65 S-17 SPT 30 SP-SM 26.8 94 5.7 2.5 1.2 Poorly Graded Sand with Silt
B-3 70 S-18 SPT 27 30.3
B-3 75 S-19 SPT 20 30.8
21-1-22205-00121-1-22205-001-R1-AB-Table
DR
A
F
T
LABORATORY TEST SUMMARY
Boring To
p
D
e
p
t
h
(
f
t
)
Sa
m
p
l
e
N
u
m
b
e
r
Sa
m
p
l
e
T
y
p
e
Bl
o
w
C
o
u
n
t
USCS WC (%)%
G
r
a
v
e
l
%
S
a
n
d
%
F
i
n
e
s
%
C
l
a
y
-
s
i
z
e
Cu Cc Gs LL PL NP Soil Description
B-3 85 S-21 SPT 5 36.9
B-3 90 S-22 SPT 2 39.7
B-3 95 S-24 SPT 0 39.6
B-3 100 S-25 SPT 0 CL 43.8 43 26 Lean Clay
B-3 105 S-26 SPT 21 ML 34.1 28 29 NP Silt
B-3 110 S-27 SPT 15 39.8
B-3 135 S-31 SPT 50/5"SM 25.3 21 Silty Sand
B-3 140 S-33 SPT 67 12.2
21-1-22205-00121-1-22205-001-R1-AB-Table
DR
A
F
T
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
4.7
5
8
Depth(ft)SampleIdentification
10.0
17.5
30.0
45.0
55.0
65.0
85.0
95.0
Fines%TestedByllGravel%Sand%
JFL
JFL
JFL
JFL
JFL
JFL
JFL
JFL
AKV
AKV
AKV
DPO
DPO
DPO
DPO
AKV
39.1
71.3
60.0
24.1
25.0
29.6
35.5
31.1
12
21
68
38
44
58
91
6.0
7.8
13
57
78
55
39
9
94
92
87
43
22
0
2
0
Fine
Mesh Opening in Inches Grain Size in Millimeters
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
GRAIN SIZE DISTRIBUTION PLOT
SiltCoarse
Mesh Openings per Inch, U.S. Standard
2 10 0.06 0.04 0.00
3
0.00
1
0.00
2
0.00
3
0.00
8
0.0
1
0.07
50.10.213620406076.2
Grain Size (mm)
P
e
r
c
e
n
t
C
o
a
r
s
e
r
b
y
M
a
s
s
1 1/2 3/8 4 20
USCSGroupSymbol
SM
ML
OH
SP-SM
SP-SM
SM
ML
ML
3 100
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
Silty Sand
Sandy Silt
Organic Silt
Poorly Graded Sand with Silt
Poorly Graded Sand with Silt
Silty Sand
Sandy Silt
Silt with Sand
USCSGroup Name
D422
D422
D422
C136
C136
C136
C136
D422
0.00
1
0.00
4
0.00
6
0.0
4
0.0
60.3
0.0
2
0.0
3
FinesSand
2410
Pe
r
c
e
n
t
F
i
n
e
r
b
y
M
a
s
s
200 0.02 0.00
2
SHANNON & WILSON, INC. • 400 NORTH 34TH STREET • SUITE 100 • SEATTLE, WASHINGTON • 98103 • MAIN (206) 632-8020 • FAX (206) 695-6777
BORING B-1
WC%
60
ReviewBy ASTMStd.< 2um%< 20um%
0.6
40
30 0.4
Gravel
Clay-SizeMediumFineCoarse
1 1/
2
3/4 0.03 0.01 0.00
8
0.00
6
0.00
4
0.8
B-1, S-4
B-1, S-7*
B-1, S-10
B-1, S-14*
B-1, S-16*
B-1, S-18*
B-1, S-22*
B-1, S-24
21
-
1
-
2
2
2
0
5
-
0
0
1
A
_
G
S
A
_
M
A
I
N
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
5
/
1
6
* Test specimen did not meet minimum mass recommendations.
5
6
20
11
DR
A
F
T
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
4.7
5
8
Depth(ft)SampleIdentification
7.5
12.5
40.0
50.0
60.0
85.0
Fines%TestedByllGravel%Sand%
JFL
JFL
JFL
JFL
JFL
JFL
AKV
AKV
DPO
DPO
DPO
AKV
41.0
41.0
23.4
25.3
27.7
35.4
16
11
25
63
47
5.5
6.1
6.9
60
37
53
94
94
93
40
0
Fine
Mesh Opening in Inches Grain Size in Millimeters
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
GRAIN SIZE DISTRIBUTION PLOT
SiltCoarse
Mesh Openings per Inch, U.S. Standard
2 10 0.06 0.04 0.00
3
0.00
1
0.00
2
0.00
3
0.00
8
0.0
1
0.07
50.10.213620406076.2
Grain Size (mm)
P
e
r
c
e
n
t
C
o
a
r
s
e
r
b
y
M
a
s
s
1 1/2 3/8 4 20
USCSGroupSymbol
ML
SM
SP-SM
SP-SM
SP-SM
ML
3 100
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
Sandy Silt
Silty Sand
Poorly Graded Sand with Silt
Poorly Graded Sand with Silt
Poorly Graded Sand with Silt
Sandy Silt
USCSGroup Name
D422
D422
C136
C136
C136
D422
0.00
1
0.00
4
0.00
6
0.0
4
0.0
60.3
0.0
2
0.0
3
FinesSand
2410
Pe
r
c
e
n
t
F
i
n
e
r
b
y
M
a
s
s
200 0.02 0.00
2
SHANNON & WILSON, INC. • 400 NORTH 34TH STREET • SUITE 100 • SEATTLE, WASHINGTON • 98103 • MAIN (206) 632-8020 • FAX (206) 695-6777
BORING B-2
WC%
60
ReviewBy ASTMStd.< 2um%< 20um%
0.6
40
30 0.4
Gravel
Clay-SizeMediumFineCoarse
1 1/
2
3/4 0.03 0.01 0.00
8
0.00
6
0.00
4
0.8
B-2, S-3
B-2, S-5
B-2, S-12*
B-2, S-14*
B-2, S-16*
B-2, S-21
21
-
1
-
2
2
2
0
5
-
0
0
1
A
_
G
S
A
_
M
A
I
N
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
5
/
1
6
* Test specimen did not meet minimum mass recommendations.
5
4
9
DR
A
F
T
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
4.7
5
8
Depth(ft)SampleIdentification
20.0
40.0
50.0
65.0
135.0
Fines%TestedByllGravel%Sand%
JFL
JFL
JFL
JFL
JFL
DPO
DPO
AKV
DPO
DPO
46.5
23.0
26.1
26.8
25.3
1742
6.4
5.1
5.7
21
55
93
95
94
3
0
Fine
Mesh Opening in Inches Grain Size in Millimeters
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
GRAIN SIZE DISTRIBUTION PLOT
SiltCoarse
Mesh Openings per Inch, U.S. Standard
2 10 0.06 0.04 0.00
3
0.00
1
0.00
2
0.00
3
0.00
8
0.0
1
0.07
50.10.213620406076.2
Grain Size (mm)
P
e
r
c
e
n
t
C
o
a
r
s
e
r
b
y
M
a
s
s
1 1/2 3/8 4 20
USCSGroupSymbol
SM
SP-SM
SP-SM
SP-SM
SM
3 100
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
Silty Sand
Poorly Graded Sand with Silt
Poorly Graded Sand with Silt
Poorly Graded Sand with Silt
Silty Sand
USCSGroup Name
D422
D422
D422
D422
D1140
0.00
1
0.00
4
0.00
6
0.0
4
0.0
60.3
0.0
2
0.0
3
FinesSand
2410
Pe
r
c
e
n
t
F
i
n
e
r
b
y
M
a
s
s
200 0.02 0.00
2
SHANNON & WILSON, INC. • 400 NORTH 34TH STREET • SUITE 100 • SEATTLE, WASHINGTON • 98103 • MAIN (206) 632-8020 • FAX (206) 695-6777
BORING B-3
WC%
60
ReviewBy ASTMStd.< 2um%< 20um%
0.6
40
30 0.4
Gravel
Clay-SizeMediumFineCoarse
1 1/
2
3/4 0.03 0.01 0.00
8
0.00
6
0.00
4
0.8
B-3, S-8*
B-3, S-12
B-3, S-14
B-3, S-17
B-3, S-31
21
-
1
-
2
2
2
0
5
-
0
0
1
A
_
G
S
A
_
M
A
I
N
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
5
/
1
6
* Test specimen did not meet minimum mass recommendations.
5DR
A
F
T
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70 80 90 100 110
SHANNON & WILSON, INC. • 400 NORTH 34TH STREET • SUITE 100 • SEATTLE, WASHINGTON • 98103 • MAIN (206) 632-8020 • FAX (206) 695-6777
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
JFL
JFL
JAA
JAA
WC%
76.3
42.4
Gravel%ReviewBy< 2um%l
D4318
D4318
PLASTICITY CHART
A-lin
e
Pla
s
t
i
c
i
t
y
I
n
d
e
x
-
P
I
U-lin
e
CL or OL
CL-ML ML or OL
MH or OH
21
-
1
-
2
2
2
0
5
-
0
0
1
A
_
A
T
T
_
M
A
I
N
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
5
/
1
6
CH or OH
Depth(ft)
25.0
100.0
SampleIdentification
BORING B-1
ASTMStd.TestedBy
USCSGroupSymbol
OH
ML
Sand%Fines%USCSGroup Name
Organic Silt
Silt
B-1, S-9
B-1, S-25
Liquid Limit - LL
PL PI
34
10
52
27
86
37
LLDR
A
F
T
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70 80 90 100 110
SHANNON & WILSON, INC. • 400 NORTH 34TH STREET • SUITE 100 • SEATTLE, WASHINGTON • 98103 • MAIN (206) 632-8020 • FAX (206) 695-6777
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
JFL
JFL
AKV
JAA
WC%
41.9
44.4
Gravel%ReviewBy< 2um%l
D4318
D4318
PLASTICITY CHART
A-lin
e
Pla
s
t
i
c
i
t
y
I
n
d
e
x
-
P
I
U-lin
e
CL or OL
CL-ML ML or OL
MH or OH
21
-
1
-
2
2
2
0
5
-
0
0
1
A
_
A
T
T
_
M
A
I
N
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
5
/
1
6
CH or OH
Depth(ft)
5.0
17.5
SampleIdentification
BORING B-2
ASTMStd.TestedBy
USCSGroupSymbol
ML
MH
Sand%Fines%USCSGroup Name
Silt
Elastic Silt
B-2, S-2
B-2, S-7
Liquid Limit - LL
PL PI
1
31
29
39
30
70
LLDR
A
F
T
vv0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70 80 90 100 110
SHANNON & WILSON, INC. • 400 NORTH 34TH STREET • SUITE 100 • SEATTLE, WASHINGTON • 98103 • MAIN (206) 632-8020 • FAX (206) 695-6777
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
JFL
JFL
JFL
AKV
JAA
AKV
WC%
34.2
43.8
34.1
Gravel%ReviewBy< 2um%l
D4318
D4318
D4318
PLASTICITY CHART
A-lin
e
Pla
s
t
i
c
i
t
y
I
n
d
e
x
-
P
I
U-lin
e
CL or OL
CL-ML ML or OL
MH or OH
21
-
1
-
2
2
2
0
5
-
0
0
1
A
_
A
T
T
_
M
A
I
N
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
5
/
1
6
CH or OH
Depth(ft)
13.5
100.0
105.0
SampleIdentification
BORING B-3
ASTMStd.TestedBy
USCSGroupSymbol
MH
CL
ML
Sand%Fines%USCSGroup Name
Elastic Silt
Lean Clay
Silt
B-3, S-5B
B-3, S-25
B-3, S-26
Liquid Limit - LL
PL PI
25
17
NP
30
26
29
55
43
28
LLDR
A
F
T
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
4.7
5
8
Depth(ft)SampleIdentification
10.0
17.5
30.0
45.0
55.0
65.0
85.0
95.0
Fines%TestedByllGravel%Sand%
JFL
JFL
JFL
JFL
JFL
JFL
JFL
JFL
AKV
AKV
AKV
DPO
DPO
DPO
DPO
AKV
39.1
71.3
60.0
24.1
25.0
29.6
35.5
31.1
12
21
68
38
44
58
91
6.0
7.8
13
57
78
55
39
9
94
92
87
43
22
0
2
0
Fine
Mesh Opening in Inches Grain Size in Millimeters
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
GRAIN SIZE DISTRIBUTION PLOT
SiltCoarse
Mesh Openings per Inch, U.S. Standard
2 10 0.06 0.04 0.00
3
0.00
1
0.00
2
0.00
3
0.00
8
0.0
1
0.07
50.10.213620406076.2
Grain Size (mm)
P
e
r
c
e
n
t
C
o
a
r
s
e
r
b
y
M
a
s
s
1 1/2 3/8 4 20
USCSGroupSymbol
SM
ML
OH
SP-SM
SP-SM
SM
ML
ML
3 100
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
Silty Sand
Sandy Silt
Organic Silt
Poorly Graded Sand with Silt
Poorly Graded Sand with Silt
Silty Sand
Sandy Silt
Silt with Sand
USCSGroup Name
D422
D422
D422
C136
C136
C136
C136
D422
0.00
1
0.00
4
0.00
6
0.0
4
0.0
60.3
0.0
2
0.0
3
FinesSand
2410
Pe
r
c
e
n
t
F
i
n
e
r
b
y
M
a
s
s
200 0.02 0.00
2
SHANNON & WILSON, INC. • 400 NORTH 34TH STREET • SUITE 100 • SEATTLE, WASHINGTON • 98103 • MAIN (206) 632-8020 • FAX (206) 695-6777
BORING B-1
WC%
60
ReviewBy ASTMStd.< 2um%< 20um%
0.6
40
30 0.4
Gravel
Clay-SizeMediumFineCoarse
1 1/
2
3/4 0.03 0.01 0.00
8
0.00
6
0.00
4
0.8
B-1, S-4
B-1, S-7*
B-1, S-10
B-1, S-14*
B-1, S-16*
B-1, S-18*
B-1, S-22*
B-1, S-24
21
-
1
-
2
2
2
0
5
-
0
0
1
A
_
G
S
A
_
M
A
I
N
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
5
/
1
6
* Test specimen did not meet minimum mass recommendations.
5
6
20
11
DR
A
F
T
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
4.7
5
8
Depth(ft)SampleIdentification
7.5
12.5
40.0
50.0
60.0
85.0
Fines%TestedByllGravel%Sand%
JFL
JFL
JFL
JFL
JFL
JFL
AKV
AKV
DPO
DPO
DPO
AKV
41.0
41.0
23.4
25.3
27.7
35.4
16
11
25
63
47
5.5
6.1
6.9
60
37
53
94
94
93
40
0
Fine
Mesh Opening in Inches Grain Size in Millimeters
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
GRAIN SIZE DISTRIBUTION PLOT
SiltCoarse
Mesh Openings per Inch, U.S. Standard
2 10 0.06 0.04 0.00
3
0.00
1
0.00
2
0.00
3
0.00
8
0.0
1
0.07
50.10.213620406076.2
Grain Size (mm)
P
e
r
c
e
n
t
C
o
a
r
s
e
r
b
y
M
a
s
s
1 1/2 3/8 4 20
USCSGroupSymbol
ML
SM
SP-SM
SP-SM
SP-SM
ML
3 100
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
Sandy Silt
Silty Sand
Poorly Graded Sand with Silt
Poorly Graded Sand with Silt
Poorly Graded Sand with Silt
Sandy Silt
USCSGroup Name
D422
D422
C136
C136
C136
D422
0.00
1
0.00
4
0.00
6
0.0
4
0.0
60.3
0.0
2
0.0
3
FinesSand
2410
Pe
r
c
e
n
t
F
i
n
e
r
b
y
M
a
s
s
200 0.02 0.00
2
SHANNON & WILSON, INC. • 400 NORTH 34TH STREET • SUITE 100 • SEATTLE, WASHINGTON • 98103 • MAIN (206) 632-8020 • FAX (206) 695-6777
BORING B-2
WC%
60
ReviewBy ASTMStd.< 2um%< 20um%
0.6
40
30 0.4
Gravel
Clay-SizeMediumFineCoarse
1 1/
2
3/4 0.03 0.01 0.00
8
0.00
6
0.00
4
0.8
B-2, S-3
B-2, S-5
B-2, S-12*
B-2, S-14*
B-2, S-16*
B-2, S-21
21
-
1
-
2
2
2
0
5
-
0
0
1
A
_
G
S
A
_
M
A
I
N
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
5
/
1
6
* Test specimen did not meet minimum mass recommendations.
5
4
9
DR
A
F
T
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
4.7
5
8
Depth(ft)SampleIdentification
20.0
40.0
50.0
65.0
135.0
Fines%TestedByllGravel%Sand%
JFL
JFL
JFL
JFL
JFL
DPO
DPO
AKV
DPO
DPO
46.5
23.0
26.1
26.8
25.3
1742
6.4
5.1
5.7
21
55
93
95
94
3
0
Fine
Mesh Opening in Inches Grain Size in Millimeters
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
GRAIN SIZE DISTRIBUTION PLOT
SiltCoarse
Mesh Openings per Inch, U.S. Standard
2 10 0.06 0.04 0.00
3
0.00
1
0.00
2
0.00
3
0.00
8
0.0
1
0.07
50.10.213620406076.2
Grain Size (mm)
P
e
r
c
e
n
t
C
o
a
r
s
e
r
b
y
M
a
s
s
1 1/2 3/8 4 20
USCSGroupSymbol
SM
SP-SM
SP-SM
SP-SM
SM
3 100
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
Silty Sand
Poorly Graded Sand with Silt
Poorly Graded Sand with Silt
Poorly Graded Sand with Silt
Silty Sand
USCSGroup Name
D422
D422
D422
D422
D1140
0.00
1
0.00
4
0.00
6
0.0
4
0.0
60.3
0.0
2
0.0
3
FinesSand
2410
Pe
r
c
e
n
t
F
i
n
e
r
b
y
M
a
s
s
200 0.02 0.00
2
SHANNON & WILSON, INC. • 400 NORTH 34TH STREET • SUITE 100 • SEATTLE, WASHINGTON • 98103 • MAIN (206) 632-8020 • FAX (206) 695-6777
BORING B-3
WC%
60
ReviewBy ASTMStd.< 2um%< 20um%
0.6
40
30 0.4
Gravel
Clay-SizeMediumFineCoarse
1 1/
2
3/4 0.03 0.01 0.00
8
0.00
6
0.00
4
0.8
B-3, S-8*
B-3, S-12
B-3, S-14
B-3, S-17
B-3, S-31
21
-
1
-
2
2
2
0
5
-
0
0
1
A
_
G
S
A
_
M
A
I
N
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
5
/
1
6
* Test specimen did not meet minimum mass recommendations.
5DR
A
F
T
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70 80 90 100 110
SHANNON & WILSON, INC. • 400 NORTH 34TH STREET • SUITE 100 • SEATTLE, WASHINGTON • 98103 • MAIN (206) 632-8020 • FAX (206) 695-6777
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
JFL
JFL
JAA
JAA
WC%
76.3
42.4
Gravel%ReviewBy< 2um%l
D4318
D4318
PLASTICITY CHART
A-lin
e
Pla
s
t
i
c
i
t
y
I
n
d
e
x
-
P
I
U-lin
e
CL or OL
CL-ML ML or OL
MH or OH
21
-
1
-
2
2
2
0
5
-
0
0
1
A
_
A
T
T
_
M
A
I
N
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
5
/
1
6
CH or OH
Depth(ft)
25.0
100.0
SampleIdentification
BORING B-1
ASTMStd.TestedBy
USCSGroupSymbol
OH
ML
Sand%Fines%USCSGroup Name
Organic Silt
Silt
B-1, S-9
B-1, S-25
Liquid Limit - LL
PL PI
34
10
52
27
86
37
LLDR
A
F
T
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70 80 90 100 110
SHANNON & WILSON, INC. • 400 NORTH 34TH STREET • SUITE 100 • SEATTLE, WASHINGTON • 98103 • MAIN (206) 632-8020 • FAX (206) 695-6777
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
JFL
JFL
AKV
JAA
WC%
41.9
44.4
Gravel%ReviewBy< 2um%l
D4318
D4318
PLASTICITY CHART
A-lin
e
Pla
s
t
i
c
i
t
y
I
n
d
e
x
-
P
I
U-lin
e
CL or OL
CL-ML ML or OL
MH or OH
21
-
1
-
2
2
2
0
5
-
0
0
1
A
_
A
T
T
_
M
A
I
N
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
5
/
1
6
CH or OH
Depth(ft)
5.0
17.5
SampleIdentification
BORING B-2
ASTMStd.TestedBy
USCSGroupSymbol
ML
MH
Sand%Fines%USCSGroup Name
Silt
Elastic Silt
B-2, S-2
B-2, S-7
Liquid Limit - LL
PL PI
1
31
29
39
30
70
LLDR
A
F
T
vv0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70 80 90 100 110
SHANNON & WILSON, INC. • 400 NORTH 34TH STREET • SUITE 100 • SEATTLE, WASHINGTON • 98103 • MAIN (206) 632-8020 • FAX (206) 695-6777
Strander Boulevard Extension Phase 3 Project
Preliminary Design - Geotechnical
Tukwila, Washington
JFL
JFL
JFL
AKV
JAA
AKV
WC%
34.2
43.8
34.1
Gravel%ReviewBy< 2um%l
D4318
D4318
D4318
PLASTICITY CHART
A-lin
e
Pla
s
t
i
c
i
t
y
I
n
d
e
x
-
P
I
U-lin
e
CL or OL
CL-ML ML or OL
MH or OH
21
-
1
-
2
2
2
0
5
-
0
0
1
A
_
A
T
T
_
M
A
I
N
2
1
-
2
2
2
0
5
.
G
P
J
S
H
A
N
_
W
I
L
.
G
D
T
1
1
/
1
5
/
1
6
CH or OH
Depth(ft)
13.5
100.0
105.0
SampleIdentification
BORING B-3
ASTMStd.TestedBy
USCSGroupSymbol
MH
CL
ML
Sand%Fines%USCSGroup Name
Elastic Silt
Lean Clay
Silt
B-3, S-5B
B-3, S-25
B-3, S-26
Liquid Limit - LL
PL PI
25
17
NP
30
26
29
55
43
28
LLDR
A
F
T
21-1-22205-001
APPENDIX C
GROUNDWATER FLOW MODELING
21-1-22205-001_R1_AC/wp/lmr 21-1-22205-001 C-i
APPENDIX C
GROUNDWATER FLOW MODELING
TABLE OF CONTENTS
Page
C.1 INTRODUCTION ...........................................................................................................C-1
C.2 CONCEPTUAL SITE MODEL ......................................................................................C-1
C.2.1 Hydrostratigraphy ..............................................................................................C-1 C.2.2 Hydraulic Properties ..........................................................................................C-2 C.2.3 Hydrology ..........................................................................................................C-2
C.2.4 Groundwater Levels and Flow ..........................................................................C-3
C.2.5 Water Budget .....................................................................................................C-4
C.3 NUMERICAL MODEL DEVELOPMENT ....................................................................C-4 C.3.1 Model Code .......................................................................................................C-4 C.3.2 Model Domain and Mesh ..................................................................................C-5
C.3.3 Modeled Hydraulic Properties ...........................................................................C-5
C.3.4 Sources and Sinks ..............................................................................................C-5
C.4 MODEL CALIBRATION ...............................................................................................C-6 C.4.1 Overview ...........................................................................................................C-6 C.4.2 Pre-Phase 2 Conditions (Steady-state) ..............................................................C-6
C.4.3 2010 Pumping Test (Short-term transient) ........................................................C-6
C.4.4 October 2014 – November 2016 (Long-term transient) ....................................C-7
C.5 PREDICTIVE SIMULATIONS ......................................................................................C-8 C.5.1 Overview ...........................................................................................................C-8
C.5.2 Base Case Results ..............................................................................................C-8
C.5.3 Mitigation Cases .....................................................................................................C-9
C.5.4 Sensitivity Analysis .........................................................................................C-10
C.6 REFERENCES ..............................................................................................................C-11
21-1-22205-001_R1_AC/wp/lmr 21-1-22205-001 C-ii
TABLES
C-1 Summary of Hydraulic Conductivity Values by Hydrogeologic Unit C-2 Modeled Hydrogeologic Units and Layering
C-3 Final Modeled Hydraulic Properties by Unit
C-4 Estimated Groundwater Inflow into Underdrain System - Phase 3 Base Case
C-5 Estimated Water Budget for Stormwater Pond - Phase 3 Base Case C-6 Estimated Water Budget for Phase 3 Mitigation Cases C-7 Calibration Sensitivity Analysis Parameters
FIGURES C-1 Previous and Phase 3 Exploration Plan
C-2 Hydrogeologic Section West-East Through Project Area
C-3 Hydrogeologic Section North-South Through Project Area
C-4 Hydrogeologic Section North-South Through Project Area C-5 WSDOT Springbrook Wetland Mitigation Bank Project Location C-6 Monthly Precipitation and Green River Stage: October 2012 – October 2016
C-7 Modeled Monthly Recharge Factors
C-8 Groundwater Levels - Springbrook Wetland Project Unit C
C-9 Groundwater Model Doman and Computational Mesh C-10 3D Model View Showing Layering and Physical Features C-11 Modeled Hydrogeologic Units and Internal Boundary Conditions – Layers 1, 2 &
3
C-12 Modeled Hydrogeologic Units – Layers 4, 5 & 6
C-13 Simulated Average Annual Groundwater Levels – Pre-Phase 2 Conditions C-14 Transient Calibration Results – 2010 Pumping Test Simulation
C-15 Simulated Constant Head Boundaries for Calibration: October 2014 – November
2016
C-16 Monthly Precipitation and Modeled Recharge for Calibration: Oct 2014 - Nov
2016 C-17 Transient Calibration Results – Phase 2 Underdrain Groundwater Inflow
C-18 Transient Calibration Results – Groundwater Levels
C-19 Phase 3 Model Computational Mesh, Drain Areas and Stormwater Pond
C-20 Simulated Groundwater Levels – Phase 3 Base Case: Average Annual Hydrology
C-21 Simulated Groundwater Levels – Phase 3 Case A: Average Annual Hydrology C-22 Simulated Groundwater Levels – Phase 3 Case B: Average Annual Hydrology
C-23 Simulated Groundwater Levels – Phase 3 Case C: Average Annual Hydrology
C-24 Simulated Groundwater Levels – Phase 3 Case D: Average Annual Hydrology
21-1-22205-001_R1_AC/wp/lmr 21-1-22205-001 C-1
APPENDIX C
GROUNDWATER FLOW MODELING
C.1 INTRODUCTION
This appendix presents our groundwater flow modeling analysis for the proposed Phase 3 design
at the Strander Boulevard Expansion Phase 3 project in Tukwila, Washington (Figure C-1). We
developed and used a groundwater flow model (the model) to estimate the likely groundwater
inflow flux into the planned Phase 3 underdrain system and infiltration at the stormwater pond
for a series of hydrologic conditions. The modeling involved the following steps:
Develop a conceptual site model (CSM) for the project area which incorporates quantitative components of local hydrology (surface water levels and precipitation-
derived recharge) and hydrogeology (aquifer/aquitard properties, groundwater levels
and gradient, discharge at the Phase 2 drain system).
Building the model using the United States Geological Survey’s code MODFLOW-USG (Panday and others, 2015) and the graphical-user interface program GMS version 10 (Aquaveo, 2016) based on the CSM.
Calibrating the model to reasonably reproduce historic data (recorded groundwater
levels and pumping station flows, and S&W’s 2010 pumping test using well TW-1)
(S&W, 2011).
Simulating the currently planned Phase 3 underdrain system to predict discharge rates and infiltration capacity of the stormwater pond.
Evaluate a series of discharge mitigation options to reduce the volume of water to be
disposed of.
C.2 CONCEPTUAL SITE MODEL
The CSM is a representation of the hydrogeologic conditions at the site. Our CSM includes the
geology, aquifer properties, hydrology, and the existing underdrain system.
C.2.1 Hydrostratigraphy
The hydrostratigraphy that impacts the underdrain system of the Strander Boulevard
Extension includes an unconfined aquifer consisting of silty sand alluvium and a confined
aquifer consisting of a sandy alluvium (upper Ha unit). The confining units (aquitards) above
and below the confined aquifer consists of silty estuarine deposits (He unit). We identified a
deeper aquifer (lower Ha unit) and installed a VWP in boring B-3 within it to measure
groundwater levels. Based on groundwater level monitoring and our numeric modeling, we
21-1-22205-001_R1_AC/wp/lmr 21-1-22205-001 C-2
determined the deeper aquifer does not significantly affect the groundwater inflow to the
underdrains. We used geologic information from the subsurface explorations completed for the
current and previous phases to develop the site hydrostratigraphy. Figures C-2, C-3 and C-4 are
hydrostratigraphic sections of the site hydrostratigraphy.
C.2.2 Hydraulic Properties
The primary aquifer properties include the hydraulic conductivity and storage coefficients
(specific yield and specific storage) for the three hydrogeologic units.
We estimated the hydraulic conductivity using grain size data, slug test results, and
pumping test results from the pumping test completed during 2010. The results of the grain size
analysis and slug test provided lower hydraulic conductivity values (9 to 48 ft/day) for the upper
Ha aquifer than the pumping test results (48 to 125 ft/day). We assume the pumping test results
are more accurate values as the pumping test stressed a larger volume of the aquifer and were
affected by boundary conditions; the grain size analysis is an indirect measurement and slug test
measures a small portion of the aquifer. We used the grain size and slug test data to help
correlate the hydraulic conditions throughout the aquifer and aquitard. Table C-1 summarizes
the overall range of hydraulic conductivity values for the main hydrogeologic units by method.
No testing was performed for the storage coefficients for the Phase 3 exploration.
However, the 2010 pumping test for the Phase 2 design produced a storativity (which is equal to
the product of the specific storage and the aquifer thickness) for the upper Ha aquifer between
6.9 x 10-4 and 7.7 x 10-4. For an aquifer thickness between 30 and 75 feet, the specific storage
would be between 9 x 10-6 and 3 x 10-5 per foot.
C.2.3 Hydrology
The main local hydrology components include direct precipitation, surface run-off on
relatively impermeable surfaces (such as asphalt, concrete, and roofs), infiltration as recharge to
the subsurface, a major river (Green River), and a series of wetlands to the south and east
associated with Springbrook Creek (Figure C-5). Based on the groundwater and river stage data
we have obtained, surface and groundwater interchange occurs between the river and the aquifers
depending on season.
We collected daily precipitation data for three nearby weather stations. These stations are
Seattle Tacoma International Airport (Seatac), Renton Airport and southeast Renton. Figure C-6
shows the monthly precipitation for the Renton Airport station, and the Green River stage for the
period between October 2012 and October 2016 (USGS, 2016).
21-1-22205-001_R1_AC/wp/lmr 21-1-22205-001 C-3
The long-term annual average precipitation is 36 inches. More than 60 percent of the
total annual precipitation occurs during the months November through March. The water years
2015 (30.1 inches) and 2016 (39.2 inches) were drier and wetter than average, respectively.
For the purpose of model development and calibration, we estimated precipitation-
derived recharge using monthly factors (recharge equal to a percentage of precipitation) ranging
from zero (for June, July, and August) to 40 percent (for December and January) (Figure C-7).
The annual average was equal to 16% of total annual precipitation.
The average river stage for the water year 2016 was elevation 14.1 feet, with daily
average winter high and summer lows of elevations 27.1 feet and 10.3 feet. Normal summer
levels are typically between elevations 10 and 12 feet.
We estimated surface run-off for the area captured by the Phase 2 drain system using the
Rational Method which accounts for precipitation and areas of different land cover types (gravel,
pavement/roof, and lawn) and a runoff coefficient for each. Between February 2015 and October
2016, the peak daily and peak weekly average runoff rates were 61 gpm and 24 gpm,
respectively.
As discussed in Appendix A, we monitored the stormwater pond stage and wetland
standing water level at the pond’s overflow structure (Figure A-6).
C.2.4 Groundwater Levels and Flow
As discussed in Appendix A, we commenced measuring and recording groundwater
levels in three monitoring wells (B-1-ow, B-2-ow, and B-3-ow) using pressure transducer/data
logger instruments, and in VWPs B-2-vwp and B-3-vwp in April 2016 (Figure A-5).
The groundwater levels in the He unit (B-2-vwp) were between elevation 21.5
feet (in April 2016) to below elevation 17 feet (when the probe became dry.
The groundwater levels in the upper Ha aquifer (B-1-ow, B-2-ow, and B-3-ow) ranged from a high of 13 feet (in April 2016) to 9 feet (in September
2016). The hydraulic gradient in the upper Ha aquifer was consistently to the
east (towards the Phase 2 underdrain system).
The groundwater levels in the lower Ha aquifer (B-3-vwp) ranged from elevation 12.5 feet (in April 2016) to elevation 9.25 feet (in August 2016). The levels were slightly higher than in the three shallower wells in the
summer but lower in the spring and fall.
We obtained groundwater level data for the period October 2011 through February 2016
for three monitoring wells that are part of the Springbrook Wetland Mitigation Project managed
21-1-22205-001_R1_AC/wp/lmr 21-1-22205-001 C-4
jointly by WSDOT and the City of Renton (Figure C-8). These wells are SBC-1, SBC-2 and
SBC-3, and are screened between 10 and 20 feet bgs (approximately between elevations -5 and -
15 feet). Note: as no reference elevations are available for the wells, these data are height of
water above a pressure transducer. As such, we were unable to determine a hydraulic gradient
across the project area. However, the available data indicate that groundwater levels fluctuate
annual by between 5 and 8 feet, and the trends are similar to those for the Green River.
C.2.5 Water Budget
We developed a conceptual water budget for the Phase 2 system during the period
February 2015 through October 2016 (see Figure 6). The key inflow and outflow components
are as follows:
Total inflow to the Phase 3 system = surface runoff (from precipitation events) plus groundwater entering the underdrains
o Total inflow daily average = 17 to 490 gpm
o Surface runoff daily average = zero and 60 gpm
o Estimated groundwater inflow = 13 to 480 gpm
Assuming the total inflow to the Phase 3 system is pumped to the stormwater pond with
no losses:
Pond Overflow = Total Phase 2 system inflow – pond infiltration -
evaporation
Water in the pond either infiltrates the surficial soils (silt and clay He unit), evaporates, or
overflows the pond weir to the wetlands (when the infiltration and evaporative capacities are
exceeded). No infiltration rate testing was performed for the pond during construction.
However, for a pond area of 31,230 sq. ft (0.72 acres) and a vertical permeability between 0.05
and 0.25 ft/day, the infiltration flux would be between 8 and 40 gpm. The overflow discharge
from the pond has not been formally monitored. However, in May 2016 and October 2016, we
measured overflow rates of 25 gpm and 57 gpm, respectively. At those times, the total inflow to
the pump station was 67 gpm and 92 gpm. Therefore, the approximate pond infiltration rates at
those times were 42 gpm and 35 gpm.
C.3 NUMERICAL MODEL DEVELOPMENT
C.3.1 Model Code
The model uses the United States Geological Survey’s code MODFLOW-USG (Panday
and others, 2015) and the graphical user interface program GMS (version 10; Aquaveo, 2016) to
21-1-22205-001_R1_AC/wp/lmr 21-1-22205-001 C-5
simulate groundwater conditions at the project site and surrounding area. MODFLOW-USG
supports a wide variety of structured and unstructured grid types, including nested grids and
grids based on prismatic triangles, rectangles, hexagons, and other cell shapes. We used this
flexibility in grid design to focus resolution around the existing and planned underdrain system
and the stormwater pond.
C.3.2 Model Domain and Mesh
Figure C-9 shows the model domain, boundaries and computational mesh in plan view.
The model occupies an area approximately 2,800 feet by 2,000 feet, centered on the Strander
Boulevard project. The model uses eight discrete layers to represent the hydrostratigraphy
extending from land surface to elevation -75 feet (total thickness of approximately 105 feet).
The smallest cells are 5 feet by 5 feet, centered on the Phase 2 and planned Phase 3 project area.
The outer cells are 20 feet by 20 feet. Figure C-10 shows the model layering in a rotated three-
dimensional view. The model’s upper surface is based on the most recent LiDAR data set. The
model uses eight layers to represent the upper 100 feet of unconsolidated soil.
C.3.3 Modeled Hydraulic Properties
Figures C-11 and C-12 show the modeled hydrogeologic units in each layer (Table C-2).
The primary hydraulic properties for the various units are horizontal and vertical hydraulic
conductivity (Kh and Kv), and the confined and unconfined storage coefficients (specific storage
and specific yield). These parameters were varied during model calibration to obtain the best
available match for groundwater levels and groundwater flow to the phase drains. The main
sources of data for the hydraulic conductivity values are the 2010 pumping test, the 2016 slug
tests, and the results of the grain size analysis (Table C-1). The pumping test also provided a
basis for the storage coefficient for the upper Ha aquifer.
C.3.4 Sources and Sinks
The primary sources of recharge to the area that we included in the model are: (1)
recharge as infiltration of precipitation (applied to the model’s uppermost layer), (2) inflow from
the Green River and from the wetland area to the east, and (3) infiltration via the stormwater
pond. The primary modeled discharges are (1) seepage to the river and (2) discharge to the
Phase 2 underdrain system. The model presents these sources and sinks as follows:
Precipitation-derived recharge – is an applied flux based on a percentage of
reported precipitation, ranging from zero to 40 percent.
Recharge at pond – is calculated by the model using the MODFLOW General
Head boundary condition with a pond stage of elevation 23 feet.
21-1-22205-001_R1_AC/wp/lmr 21-1-22205-001 C-6
Green River inflow/outflow – uses the time-varying MODFLOW Constant
Head condition with the head equal to the reported river stage.
Eastern boundary inflow/outflow – uses the time-varying Constant Head condition with the head interpreted from the groundwater level data obtained
for the Springbrook wetland piezometers (Figure C-7).
Outflow at Phase 2 drains – is calculated by the model using the MODFLOW
Drain function. The elevation assigned to each Drain condition varied between cells and was based on the as-built records (between elevations 7 and 20 feet). Drain conditions were inserted into model layers 1, 2 and 3,
depending on the
C.4 MODEL CALIBRATION
C.4.1 Overview
We calibrated the model to the following data sets:
Pre-Phase 2 conditions (steady-state), to establish a stable model and initial
groundwater levels.
The 24-hour constant rate pumping test performed for Phase 2 using well TW-1 (in 2010), and
The historical groundwater level and Phase 2 underdrain system discharge
data for the 21 month period from February 2015 through October 2016.
C.4.2 Pre-Phase 2 Conditions (Steady-state)
Once the model was revised, we simulated pre-Phase 2 conditions. This involved
assigning constant heads of elevation 16.3 feet to the Green River (equal to the annual average
daily stage for water year 2012) and elevation 18.0 feet to the eastern boundary. We assigned an
average annual recharge rate of 5.9 inches, equal to 16.3 percent of the annual precipitation,
uniformly across the area (despite variable soil and land uses).
Figure C-13 shows the resulting groundwater level contours in the upper part of the Ha
unit (model layer 5). Groundwater flows from east to west, discharging to the river boundary.
We used these simulated groundwater levels as initial heads for transient calibration (see below)
and the predictive simulations.
C.4.3 2010 Pumping Test (Short-term transient)
We used the pre-Phase 2 steady-state model to simulate the aquifer pumping that we
performed for the Phase 2 design in 2010 (S&W, 2011). The test involved pumping test well
21-1-22205-001_R1_AC/wp/lmr 21-1-22205-001 C-7
PW-1 (screened in the Ha unit) for 24 hours at an average rate of 208 gpm, shutting off pumping,
and measuring changes in groundwater level (drawdown) in three monitoring wells (MW-1,
MW-3 and MW-4; shown on Figure 2). Our analytical interpretation of the pumping test
resulted in a range of hydraulic conductivities for the upper Ha unit between 48 and 125 ft/day
and a storativity between 6.9 x 10-4 and 7.7 X 10-4.
Figure C-14 shows the observed and model-estimated drawdown for these three
monitoring wells during the pumping and recovery phases. The modeled horizontal and vertical
hydraulic conductivity of the Ha unit was 80 ft/day and 16 ft/day, respectively, and the
storativity was 4 x 10-3. Overall, the model reproduced the observed drawdown in wells MW-3
and MW-4 (2.3 feet and 3.3 feet), but over-predicted the drawdown in well MW-1 by one foot.
C.4.4 October 2014 – November 2016 (Long-term transient)
We then simulated an extended time period to complete the calibration process. This
period extended from October 1, 2014 through November 2, 2016 using 109 weekly stress
periods. The primary model inputs were as follows:
Green River – a time-varying Constant Head condition using weekly average
stage levels from the USGS Tukwila station; levels ranged from elevation
10.5 feet to elevation 25.2 feet (Figure C-14).
Eastern boundary - time-varying Constant Head condition using interpreted
elevations based on the available groundwater level data from the Springbrook
wetland piezometers feet; modeled levels ranged between elevations 12.0 feet
and 190 feet (Figure C-14).
Precipitation-derived recharge – based on recorded weekly precipitation and monthly factors that range from zero (for June-August) to 40 percent (for
December and January) (Figure C-15).
Phase 2 Drains – uses the MODFLOW Drain boundary condition (described
in Section C.3.4), commencing on February 25, 2015.
Phase 2 Pond – uses the MODFLOW General Head boundary conditions (described in Section C.3.4). Pond stage was maintained at elevation 23 feet
throughout the simulation period.
The primary calibration observation data were:
Groundwater levels in wells B-1-ow, B-2-ow, and B-3-ow between April and November 2016; and
Phase 2 drain system inflow, adjusted for groundwater component (February
through October 2016).
21-1-22205-001_R1_AC/wp/lmr 21-1-22205-001 C-8
Figure C-15 show the Phase 2 groundwater inflow for the transient calibration. These
results indicate that the model over-predicts the drain system inflow during the spring and
summer of 2015 and during the summer of 2016. Although the model reasonably reproduces the
inflow during the fall and winter of 2015-2016, the accuracy of the groundwater inflow during
this period is uncertain due to very high runoff and data gaps. The model predicts that the pond
recharge ranged between 10 and 25 gpm during the calibration time period. Although no
measured recharge data exist for the pond, this range seems reasonable based on the water
budget estimates of 35 gpm and 42 gpm during 2016 (Section C.2.5).
Figure C-16 shows the Phase 2 groundwater level results for the transient calibration.
Overall, the modeled heads are between one and two feet higher than those observed in the three
monitoring wells. However, the observed seasonal trend and the hydraulic gradient between the
three wells is adequately reproduced. Table C-3 presents the final modeled hydraulic properties
for the three hydrogeologic units for the period April through October 2016.
C.5 PREDICTIVE SIMULATIONS
C.5.1 Overview
We used the calibrated model to simulate the expanded Phase 3 underdrain and stormwater pond
system for three hydrologic conditions (each run at steady-state). These conditions are:
Average annual hydrology – typical average precipitation-derived recharge (equal
to 6 inches per year, which is 16 percent of total annual precipitation); mid-year Green River stage (elevation 14 feet); and eastern boundary groundwater level (elevation 16 feet).
Normal winter season – typical winter Green River stage (elevation 20 feet) and
eastern boundary groundwater level (elevation 18 feet).
Wet winter season – high winter Green River stage (elevation 23 feet) and eastern boundary groundwater level (elevation 20 feet).
We revised the calibrated model’s computational mesh to include a denser grid in the
area of the planned Phase 3 drains and enlarged stormwater pond (Figure C-19). The smallest
cells have plan view dimensions 5 feet by 5 feet.
C.5.2 Base Case Results
Figure C-20 shows the estimated groundwater levels in model layers 1 and 3 (He unit) and in
layer 5 (upper Ha unit) for the Base Case for the average annual hydrologic condition. The
underdrain system would create an irregular shaped cone of depression with groundwater levels
as low as approximately elevation 7 feet. The stormwater pond would maintain higher
21-1-22205-001_R1_AC/wp/lmr 21-1-22205-001 C-9
groundwater levels to the south of the underdrain area. Table C-4 summarizes the model-
estimated groundwater discharge to the existing Phase 2 underdrains and to the expanded Phase
3 underdrains for the three hydrologic cases. These rates represent only the groundwater inflow
to the drains; therefore, the total inflow would also include surface run-off that the model does
not explicitly simulate. We estimate that for average annual conditions (precipitation of 36
inches per year), the drain system would collect 10 gpm on average and up to 25 gpm in winter.
The model estimates that:
The groundwater inflow to the Phase 3 underdrain system would be approximately 150
gpm for average annual conditions and approximately 355 gpm for the wet winter
condition.
Assuming that the total inflow to the pump station is conveyed to the stormwater pond,
the overflow from the pond to the wetlands could be on the order of 130 gpm (average
annual condition) and 405 gpm (wet winter condition).
These overflow rates are between 10 and 50 percent higher than those estimated by the
model for the existing Phase 2 underdrain system under the same hydrologic conditions
(120 gpm and 270 gpm, respectively).
C.5.3 Mitigation Cases
We used the model to evaluate the potential to reduce the groundwater inflows to the
Phase 3 underdrain system and limit overflows from the stormwater pond. We developed the
following concepts:
Case A – Remove the over-drilled window through the He unit in the Phase 2 excavation
by grouting.
Case B – Install low permeability cut-off walls through the He and upper Ha units
Case C – Recharge water collected at the pumping station in wells located around the stormwater pond
Case D – combined Cases A and C
Case A assumed that the permeability of the over-excavated window through the base of the He
unit could be reduced by grouting. In practice, this would likely involve removal of some of the
existing structures. We simulated this option by decreasing the hydraulic conductivity of the
material in model layers 3 and 4 (the lower half of the He unit) from 250 ft/day to 0.5 ft/day.
This case was run for the three hydrologic conditions.
21-1-22205-001_R1_AC/wp/lmr 21-1-22205-001 C-10
Case B involved installing impermeable sheet walls around the northern, eastern, and southern
ends of the Phase 2 underdrains where the over-excavation took place. The goal of this action
was to reduce inflow from the upper Ha unit. We simulated three wall depths, one each
extending from ground surface to elevations -5 feet, -25 feet, and -50 feet. We ran these three
cases only for the average hydrologic condition.
Case C involved simulating six shallow groundwater wells that re-inject water removed at the
pump station as a means to reduce (or eliminate) the overflow from the pond. The wells were
simulated to recharge to the middle part of the upper Ha unit (model layers 6 and 7). The
analysis consisted of an iterative process during which the number of wells and their assigned
recharge rates were balanced to roughly equal the model-estimated inflow to the pumping station
minus losses from evaporation and pond infiltration. This case was run for the three hydrologic
conditions.
Table C-6 summarizes the estimated water budget results for these mitigation cases. Figures C-
21 through C-24 show the modeled steady-state groundwater levels for Cases A, B, C, and D for
the average annual hydrologic condition. The results indicate the following:
For Case A, grouting the window through the relatively low permeability He unit, the
groundwater inflow to the Phase 3 underdrains and the pond overflow would be
between 50 gpm (average) and 115 gpm (wet winter). The estimated pond overflow
rates are 35 gpm and 165 gpm, which are 25 and 40 percent of those estimated for the Base Case.
For Case B, the cut-off wall options would have negligible effects on groundwater
inflows to the Phase 3 system. This option would only be beneficial if the wall could
be keyed into a low permeability soil unit to reduce vertical flow from the lower part
of the Ha unit.
For Case C, the six recharge well option could theoretically greatly reduce the
overflow from the stormwater pond (despite increasing the groundwater inflow to the
pumping system by between 10 and 20 percent). However, there would be significant
practical challenges in operating and maintaining these wells.
The hybrid Case D would reduce the required recharge rate for each well from 165 gpm (for Case C) to 55 gpm for the average hydrology condition. This would make
this option more practically feasible.
C.5.4 Sensitivity Analysis
As part of the long-term transient calibration, we evaluated the sensitivity of the model-
estimated groundwater inflow into the Phase 2 underdrain system and stormwater pond recharge
to uncertainty in key model parameters. Table C-7 presents the sensitivity cases and parameters.
These parameters are:
21-1-22205-001_R1_AC/wp/lmr 21-1-22205-001 C-11
Hydraulic conductivity (horizontal and vertical) for the He, Ha(o), and upper
Ha units.
Specific yield and specific storage for the upper Ha unit.
Drain and stormwater pond bed conductance values.
The percentage of annual precipitation that is assigned as surficial recharge.
We evaluated parameter values that were higher and lower than the final calibration
values. Overall, the analysis indicated that the groundwater discharge to the drains was most
sensitive to the upper Ha unit hydraulic conductivity and the drain conductance parameters. The
pond recharge was most sensitive to the He unit hydraulic conductivity.
We then developed a Phase 3 underdrain system sensitivity case that consisted of the
following:
Higher hydraulic conductivity (horizontal and vertical) for the He, Ha(o), and
upper Ha units (sensitivity cases S1, S3 and S5 in Table C-7).
Higher drain conductance (sensitivity case S9 in Table C-7).
We ran this sensitivity case for the wet winter hydrologic condition for the Base Case.
The results indicated that the groundwater inflow to the Phase 3 underdrain system would be 500
gpm, which is 40 percent higher than for the calibrated case (355 gpm; see Table C-4).
C.6 REFERENCES
Aquaveo, LLC, 2014, Groundwater modeling software GMS (v. 10.1): Provo, Utah, Aquaveo,
LLC.
Driscoll, F. G., 1986, Groundwater and wells (2nd ed.): St. Paul, Minn., Johnson Division, 1089 p.
Panday, Sorab; Langevin, C. D.; Niswonger, R. G.; and others, 2013, MODFLOW-USG version
1: An unstructured grid version of MODFLOW for simulating groundwater flow and tightly
coupled processes using a control volume finite-difference formulation: U.S. Geological
Survey Techniques and Methods 6-A45, 68 p/., available: https://pubs.er.usgs.gov/publication/tm6A45.
National Oceanic and Atmospheric Administration, 2016, Weather observations for the past three
days, Renton, Renton Municipal Airport: http://w1.weather.gov/obhistory/KRNT.html
Shannon & Wilson, Inc., 2011, Strander Boulevard underpass phase II, revised dewatering
evaluation: Report prepared by Shannon & Wilson, Inc., Seattle, Wash., 21-1-21292-003, for Berger/ABAM, Federal Way, Wash., May.
21-1-22205-001_R1_AC/wp/lmr 21-1-22205-001 C-12
U. S. Geological Survey, 2016, Provisional data subject to revisions for USGS 12113350 Green
River at Tukwila, WA: National Water Information System: Web Interface, available: http://waterdata.usgs.gov/nwis/uv?site_no=12113350, accessed November 2, 2016.
TABLE C-1
SUMMARY OF HYDRAULIC CONDUCTIVITY VALUES BY HYDROGEOLOGIC UNIT
SHANNON & WILSON, INC.
Pumping Test1 Slug Tests2 Grain Size Analysis3
ft/d <0.01 - 0.4
cm/sec <10-5 - 1.2x10-4
ft/d 48 - 125 9 - 48 1.1 - 88
cm/sec 1.7x10-2 - 4.4 x10-2 3.3x10-3 - 1.7x10-2 4x10-3 - 3x10-2
ft/d <0.01 - 10
cm/sec <10-5 - 3x10-3
Notes:
1 - 2010 constant rate test using PW-1 (S&W, 2011)
2 - using the Bouwer & Rice solution
3 - using empirical methods in Odong, 2007
NA - not analyzed
ft/d - feet per day
cm/sec - centimeter per second
Hydrogeologic Unit
Method
NA
Lower Ha NA NA
Unit
Upper Ha
He and Ha(0) NA
Appendix C - tables 21-1-22205-001DRAFT
TABLE C-2
MODELED HYDROGEOLOGIC UNITS AND LAYERING
SHANNON & WILSON, INC.
Model Layer(s)Unit(s)Elevation Range
1 He and Ha(o)Land to +10 ft
2 - 4 He and Ha(o)+10 ft to zero
5 Upper Ha and He zero to -5 ft
6 - 8 Upper Ha -5 to -75 ft
Appendix C - tables 21-1-22205-001DRAFT
TABLE C-3
FINAL MODELED HYDRAULIC PROPERTIES BY UNIT
SHANNON & WILSON, INC.
Hydrogeologic Unit Layer(s) Kh (ft/d) Kv (ft/d) Sy (-) Ss (per ft)
He 1 - 4 1 0.1 0.05 5 x 10-5
Ha(o)1 - 4 2.5 0.25 0.1 5 x 10-5
Upper Ha 5 - 8 80 16 0.1 5 x 10-5
Notes:
ft/d - feet per day
Kh - horizontal hydraulic conductivity
Kv - vertical hydraulic conductivity
Sy - specific yield
Ss - specific strage (=thickness x storativity)
Appendix C - tables 21-1-22205-001DRAFT
TABLE C-4
ESTIMATED GROUNDWATER INFLOW INTO UNDERDRAIN SYSTEM - PHASE 3 BASE CASE
SHANNON & WILSON, INC.
Existing
Underdrain New Underdrain Total Inflow
Average annual 120 75 75 150
Normal winter 200 125 130 255
Wet winter 245 155 200 355
Note:
units = gallons per minute
Hydrologic Case
Existing Phase 2
Underdrain System
Expanded Phase 3 Underdrain System
Appendix C - tables 21-1-22205-001
TABLE C-5
ESTIMATED WATER BUDGET FOR STORMWATER POND - PHASE 3 BASE CASE
SHANNON & WILSON, INC.
Average annual 160 (150 + 10) 5 25 130
Normal winter 285 (255 + 30) 0 15 270
Wet winter 415 (355 + 60) 0 10 405
Notes:
Units are gpm.
GW = groundwater
Runoff estimated using the Rational Method and precipitation data for Feb. 2016 - Oct. 2016 (data provided by BergerABAM, Nov. 3, 2016)
Hydrologic Case
Phase 3 System
(GW + Runoff)
{A}
Evaporation Loss at
Pond
{B}
Infiltration at Pond
{C}
Estimate Overflow
from Pond
{D = A-B-C}
Appendix C - tables/wp/lmr Page 1 of 1 21-1-22205-001
TABLE C-6
ESTIMATED WATER BUDGET FOR PHASE 3 MITIGATION CASES
SHANNON & WILSON, INC.
GW
Inflow
Pond
Overflow
GW
Inflow
Pond
Overflow
GW
Inflow
Pond
Overflow
GW
Inflow
Pond
Overflow
GW
Inflow
Pond
Overflow
Average
annual 150 135 50 35 130-1501 115-1301 180 5 70 0
Normal
winter 255 270 90 105 NA NA 310 35 NA NA
Wet winter 355 405 115 165 NA NA 385 45 NA NA
Notes:
GW = groundwater1 Range for three modeled wall depths.
Units are gpm.
NA = not analyzed
Case D – Combined
Grout Window &
RechargeHydrologic
Case
Expanded Phase 3
System
Case A - Grout
Window Case B – Cut-off Wall
Case C – Recharge
Wells
Appendix C - tables/wp/lmr Page 1 of 1 21-1-22205-001
TABLE C-7
CALIBRATION SENSITIVITY ANALYSIS PARAMETERS
SHANNON & WILSON, INC.
S1 2,5, 0.25
S2 0.25, 0.025
S3 5, 0.5
S4 1, 0.1
S5 100, 20
S6 60, 12
S7 0.2, 5 x 10-5
S8 0.05, 1 x 10-6
S9 25
S10 2.5
S11 25
S12 2.5
S13 20%
S14 13%
Notes:
1 - units are feet per day
2 - units are per foot
3 - units are square feet per day
Ha(o) unit - Kh, Kv1
Upper Ha unit - Kh, Kv1
Sensitivity Model ValuesParameter Changed
16%
Upper Ha unit - Sy, Ss2
Subsurface Drain Conductance3
Stormwater Pond Bed Conductance3
Precipitation-derived Recharge
1.0, 0.1
2.5, 0.25
80, 16
0.1, 1x10-5
10
10
Base Case Model
Values Sensitivity Case
He unit - Kh, Kv1
Appendix C - tables 21-1-22205-001DRAFT
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Design ‐Geotechnical
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Design ‐Geotechnical
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APPENDIX D
IMPORTANT INFORMATION ABOUT YOUR GEOTECHNICAL/ENVIRONMENTAL REPORT
Page 1 of 2 1/2016
SHANNON & WILSON, INC.
Geotechnical and Environmental Consultants
Dated:
Attachment to and part of Report 21-1-22205-001_R1
Date: December 2, 2016
To: Mr. Bob Fernandes, P.E.
BergerABAM
IMPORTANT INFORMATION ABOUT YOUR GEOTECHNICAL/ENVIRONMENTAL
REPORT
CONSULTING SERVICES ARE PERFORMED FOR SPECIFIC PURPOSES AND FOR SPECIFIC CLIENTS.
Consultants prepare reports to meet the specific needs of specific individuals. A report prepared for a civil engineer may not be adequate for a construction contractor or even another civil engineer. Unless indicated otherwise, your consultant prepared your report expressly
for you and expressly for the purposes you indicated. No one other than you should apply this report for its intended purpose without first conferring with the consultant. No party should apply this report for any purpose other than that originally contemplated without
first conferring with the consultant.
THE CONSULTANT'S REPORT IS BASED ON PROJECT-SPECIFIC FACTORS.
A geotechnical/environmental report is based on a subsurface exploration plan designed to consider a unique set of project-specific factors. Depending on the project, these may include: the general nature of the structure and property involved; its size and
configuration; its historical use and practice; the location of the structure on the site and its orientation; other improvements such as access roads, parking lots, and underground utilities; and the additional risk created by scope-of-service limitations imposed by the
client. To help avoid costly problems, ask the consultant to evaluate how any factors that change subsequent to the date of the report may affect the recommendations. Unless your consultant indicates otherwise, your report should not be used: (1) when the nature of
the proposed project is changed (for example, if an office building will be erected instead of a parking garage, or if a refrigerated warehouse will be built instead of an unrefrigerated one, or chemicals are discovered on or near the site); (2) when the size, elevation,
or configuration of the proposed project is altered; (3) when the location or orientation of the proposed project is modified; (4) when there is a change of ownership; or (5) for application to an adjacent site. Consultants cannot accept responsibility for problems that may
occur if they are not consulted after factors which were considered in the development of the report have changed.
SUBSURFACE CONDITIONS CAN CHANGE.
Subsurface conditions may be affected as a result of natural processes or human activity. Because a geotechnical/environmental report is based on conditions that existed at the time of subsurface exploration, construction decisions should not be based on a report whose adequacy may have been affected by time. Ask the consultant to advise if additional tests are desirable before construction starts; for example, groundwater conditions commonly vary seasonally.
Construction operations at or adjacent to the site and natural events such as floods, earthquakes, or groundwater fluctuations may also affect subsurface conditions and, thus, the continuing adequacy of a geotechnical/environmental report. The consultant should be kept apprised of any such events, and should be consulted to determine if additional tests are necessary.
MOST RECOMMENDATIONS ARE PROFESSIONAL JUDGMENTS.
Site exploration and testing identifies actual surface and subsurface conditions only at those points where samples are taken. The data were extrapolated by your consultant, who then applied judgment to render an opinion about overall subsurface conditions. The actual
interface between materials may be far more gradual or abrupt than your report indicates. Actual conditions in areas not sampled may differ from those predicted in your report. While nothing can be done to prevent such situations, you and your consultant can work
together to help reduce their impacts. Retaining your consultant to observe subsurface construction operations can be particularly beneficial in this respect.
Page 2 of 2 1/2016
A REPORT'S CONCLUSIONS ARE PRELIMINARY.
The conclusions contained in your consultant's report are preliminary because they must be based on the assumption that conditions revealed through selective exploratory sampling are indicative of actual conditions throughout a site. Actual subsurface conditions can
be discerned only during earthwork; therefore, you should retain your consultant to observe actual conditions and to provide conclusions. Only the consultant who prepared the report is fully familiar with the background information needed to determine whether or not the
report's recommendations based on those conclusions are valid and whether or not the contractor is abiding by applicable recommendations. The consultant who developed your report cannot assume responsibility or liability for the adequacy of the report's
recommendations if another party is retained to observe construction.
THE CONSULTANT'S REPORT IS SUBJECT TO MISINTERPRETATION.
Costly problems can occur when other design professionals develop their plans based on misinterpretation of a geotechnical/environmental report. To help avoid these problems, the consultant should be retained to work with other project design
professionals to explain relevant geotechnical, geological, hydrogeological, and environmental findings, and to review the adequacy of their plans and specifications relative to these issues.
BORING LOGS AND/OR MONITORING WELL DATA SHOULD NOT BE SEPARATED FROM THE REPORT.
Final boring logs developed by the consultant are based upon interpretation of field logs (assembled by site personnel), field test results,
and laboratory and/or office evaluation of field samples and data. Only final boring logs and data are customarily included in geotechnical/environmental reports. These final logs should not, under any circumstances, be redrawn for inclusion in architectural or
other design drawings, because drafters may commit errors or omissions in the transfer process. To reduce the likelihood of boring log or monitoring well misinterpretation, contractors should be given ready access to the complete geotechnical engineering/environmental report prepared or authorized for their use. If access is provided only to the report prepared for
you, you should advise contractors of the report's limitations, assuming that a contractor was not one of the specific persons for whom the report was prepared, and that developing construction cost estimates was not one of the specific purposes for which it was prepared.
While a contractor may gain important knowledge from a report prepared for another party, the contractor should discuss the report with your consultant and perform the additional or alternative work believed necessary to obtain the data specifically appropriate for construction cost estimating purposes. Some clients hold the mistaken impression that simply disclaiming responsibility for the accuracy of subsurface information always insulates them from attendant liability. Providing the best available information to contractors helps
prevent costly construction problems and the adversarial attitudes that aggravate them to a disproportionate scale.
READ RESPONSIBILITY CLAUSES CLOSELY.
Because geotechnical/environmental engineering is based extensively on judgment and opinion, it is far less exact than other design
disciplines. This situation has resulted in wholly unwarranted claims being lodged against consultants. To help prevent this problem, consultants have developed a number of clauses for use in their contracts, reports, and other documents. These responsibility clauses
are not exculpatory clauses designed to transfer the consultant's liabilities to other parties; rather, they are definitive clauses that identify where the consultant's responsibilities begin and end. Their use helps all parties involved recognize their individual responsibilities and
take appropriate action. Some of these definitive clauses are likely to appear in your report, and you are encouraged to read them closely. Your consultant will be pleased to give full and frank answers to your questions.
The preceding paragraphs are based on information provided by the ASFE/Association of Engineering Firms Practicing in the Geosciences, Silver Spring, Maryland
City of Renton Strander Boulevard Extension
and Union Pacific Railroad Realignment
Phase 1, Segments 2A and 2B
WETLAND TECHNICAL MEMORANDUM
PERT0000-0006
Prepared for:
CITY OF RENTON
Prepared by:
DAVID EVANS AND ASSOCIATES, INC.
415 118th Ave. SE
Bellevue, WA 98005
November 2007
City of Renton Strander Boulevard Extension
and Union Pacific Railroad Realignment
Phase 1, Segments 2A and 2B
WETLAND TECHNICAL MEMORANDUM
PERT0000-0006
Prepared for:
CITY OF RENTON
Prepared by:
Jim Shannon
Senior Fish and Wildlife Biologist
DAVID EVANS AND ASSOCIATES, INC.
415 118th Ave. SE
Bellevue, WA 98005
November 2007
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TABLE OF CONTENTS
1.0 INTRODUCTION..........................................................................................................................1
2.0 PROJECT DESCRIPTION..........................................................................................................1
3.0 REVISED WETLAND IMPACTS...............................................................................................2
4.0 WETLAND RATINGS..................................................................................................................2
4.1 Wetlands H, M, P, and S...........................................................................................................4
4.2 Wetlands A, C, D, and E...........................................................................................................4
4.3 Wetland QR...............................................................................................................................5
4.4 Wetland T..................................................................................................................................6
4.5 Mitigation Banking....................................................................................................................6
5.0 SUMMARY....................................................................................................................................7
6.0 REFERENCES...............................................................................................................................7
Tables
Table 1. Permanent and Temporary Wetland and Buffer Impacts................................................................2
Table 2. Project Wetland Classification and Jurisdiction. ............................................................................3
Appendices
Appendix 1. Vicinity Map
Appendix 2. Wetland Impacts
Appendix 3. Wetland Rating Forms
Appendix 4. Wetland Photographs
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Abbreviations and Acronyms
BNSF Burlington Northern Santa Fe Railway
City City of Renton
Corps U.S. Army Corps of Engineers
DEA David Evans and Associates, Inc.
Ecology Washington Department of Ecology
HGM hydrogeomorphic
JARPA Joint Aquatic Resources Permit Application
NEPA National Environmental Protection Act
Project Strander Boulevard Extension and Union Pacific Railroad Realignment Project –
Phase 1, Stage 2A and 2B
UPRR Union Pacific Railroad
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1.0 Introduction
At the request of the City of Renton (City), David Evans and Associates, Inc. (DEA) prepared
this Wetland Technical Memorandum for support of the Joint Aquatic Resources Permit
Application (JARPA) for the Strander Boulevard Extension and Union Pacific Railroad
Realignment Project – Phase 1, Stage 2A and 2B (Project). The project is located in the cities of
Tukwila and Renton, Washington (Appendix 1). The Project includes parts of three elements of
a larger project (Alternative 1) that received a National Environmental Protection Act (NEPA)
Categorical Exclusion and a State Environmental Protection Act Determination of Non-
significance on July 19, 2005.
This technical memorandum complements the Wetlands Technical Discipline Report, Strander
Boulevard Extension, dated May 2004, and includes a current project description, wetland
impacts, and wetland ratings using the Washington Department of Ecology (Ecology) rating
system (Hruby 2004).
2.0 Project Description
Three action alternatives were proposed in the discipline reports prepared for the NEPA.
Alternative 1 was chosen as the preferred alternative. The current project includes portions of
three elements from Alternative 1. These elements include:
1. Relocation of the Union Pacific Railroad (UPRR) tracks.
2. New roadway construction from West Valley Highway to Oaksdale Avenue SW
(overpass only).
3. Modifications to Longacres Way (bridge conveying UPRR over South Longacres Way
only).
We propose to relocate the UPRR approximately 300 feet to the east to parallel the existing two
sets of Burlington Northern Santa Fe Railway (BNSF) tracks. The relocation will begin
approximately 1,000 feet south of Southwest 27th Street and end 5,500 feet north under
Interstate 405. We estimate approximately 125,000 cubic yards of fill for the relocated track.
New roadway construction will include an overpass over the relocated track that ties to West
Valley Freeway to the west and approximately 1,000 feet to the east. It is estimated 250,000
cubic yards of fill will be used for the overpass approaches. A stormwater detention and
enhanced treatment facility will be built near the overpass.
Modifications to Longacres Way will include the construction of the UPRR bridge over
Longacres Way only. Standard railroad bridge designs will be used for this bridge.
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3.0 Revised Wetland Impacts
The proposed alignment of the UPRR relocation (Alternative 1 in DEA 2004) has changed from
its original design due to a change in the design of the new roadway overpass. The original
overpass was a bridge built on piers. Currently the design is an overcrossing with approaches
made of fill. This design change reduced total impacts to wetlands on-site but also changed
which wetlands will be impacted (Table 1; Appendix 2).
Table 1. Permanent and Temporary Wetland and Buffer Impacts.
Wetland
Impacted
Permanent
Wetland Impact
Permanent
Buffer Impact
Temporary
Wetland Impact
Temporary
Buffer Impact
(acres) (acres) (acres) (acres)
A 0.009 0.101 0.004 0.013
C 0.191 0.042 0.138 0.012
D 0.036 0.024 0.034 0.023
E 0.022 0.026 0.019 0.019
H 0 0.026 0 0.023
M 0 0.038 0 0.036
P 0.009 0 0.005 0
QR (Cat. I) 0 0 0 0
QR (Cat. II) 0.875 0.568 0.242 0.175
S 0 0.300 0 0.098
T 0.286 1.580 0.137 0.127
Total 1.430 2.846 0.599 0.526
4.0 Wetland Ratings
The study area contains nine wetlands impacted by the current design. Using scores from the
Washington State Wetland Rating System (Hruby 2004) the project will impact eight Category
III wetlands and one Category I/II wetland (Table 2). Wetland rating forms with aerial photos
used for determining ratings and wetland photos can be found in Appendices 3 and 4
respectively.
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Strander Boulevard Extension and Union Pacific Railroad Realignment Phase 1, Segments 2A and 2B
Table 2. Project Wetland Classification and Jurisdiction.
Ecology Classification
Wetland
Cowardin
Classification
HGM
Type
Water
Quality
Score
Hydrologic
Score
Habitat
Score
Total
Score
Ecology
Category Jurisdiction
Buffer
(ft)
Size
(approx.
sq ft)
A PEM D 20 24 5 49 III Tukwila 50 2,467
C PSS D 14 20 13 47 III Tukwila 80 67,870
D PSS D 16 24 8 48 III Tukwila 50 3,546
E PSS D 20 20 9 49 III Tukwila 50 1,500
H PEM D 20 20 4 44 III Tukwila 50 499
M PEM D 24 20 6 50 III Tukwila 50 5,110
P PFO D 16 20 7 43 III Tukwila 50 622
QR PSS/PFO D 22 20 16 58 I/II Tukwila 100
45,000/
1,044,000
S PEM D 20 20 6 46 III Tukwila 50 6,428
T PEM D 18 16 11 45 III Tukwila 50 21,831
The hydrogeomorphic (HGM) classification of all wetlands impacted by the Project area is
considered to be depressional, which means that the unit is in a topographic depression in which
water ponds or is saturated to the surface at some time during the year, and any outlet, if present,
is higher than the interior of the wetland (Hruby 2004).
Project wetlands have potential to improve water quality and reduce flooding and stream
degradation. The opportunity to improve water quality is provided by the presence of pollutant
sources in the close proximity or upslope of these wetlands. Pollutant sources include railroad
tracks and recreational paved trails (i.e. Interurban Trail). Water quality is improved when
wetlands trap pollutants and is a function of outlet type, vegetation density, and area of seasonal
inundation within the wetland. Hydrologic functions are provided when these wetlands store
excessive or erosive flows that may damage roadways or properties downstream. The potential
to perform hydrologic functions is provided by the characteristics of the outlets, wetland size,
and the amount of live flood storage provided. Field observations indicate that much of the
study area below the toe of fill for the railroad tracks is seasonally inundated. Additionally,
frequent flooding of the Green River and Springbrook Creek provide greater opportunity for
wetlands in the study area to provide functions that may mitigate the peak flows and reduce the
severity of flood events.
In general, the wetlands impacted by the project demonstrate a low level of habitat function.
Using the Washington State Wetland Rating System, no wetlands scored above 16 for habitat.
These wetlands generally have a moderate vegetation structure (five to nineteen species of
plants), but disturbed buffers limit vegetated connections to other wetlands in the area. Overall,
these characteristics allow for a moderate number of habitat niches, low access to the wetland,
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and low opportunities for connections to other wetlands within the greater wetland system.
However, the presence of large downed woody debris and persistent thin-stemmed vegetation in
areas subject to inundation are indications of adequate habitat for amphibians.
4.1 Wetlands H, M, P, and S
These isolated wetlands do not appear to fall under the jurisdiction of the U.S. Army Corps of
Engineers (Corps) through Section 404 of the Clean Water Act. However, the Corps has the
ultimate authority in making Section 404 jurisdictional determinations. No other wetlands
within the proposed Project alignment were determined to be isolated.
These wetlands were rated as Category III following Ecology’s rating system (Hruby 2004). The
primary function of these wetlands is water quality improvement and hydrologic storage.
Railroad and automobile activities upslope make available pollutants that provide the
opportunity for water quality improvement. All of these wetlands are densely vegetated and
have the ability to filter sediments, enhancing their ability to trap pollutants.
These wetlands are also hydrologically isolated. Any stormwater flowing into them is trapped
and does not contribute to downstream flooding.
4.2 Wetlands A, C, D, and E
Wetlands A, C, D, and E are located between the UPRR tracks and the Interurban Trail. These
wetlands were rated as Category III following Ecology’s rating system (Hruby 2004). Wetlands
A, C, D, and E are scrub/shrub with predominant species including Pacific willow and red-osier
dogwood.
These wetlands have a close proximity to the Green River. Soils and hydrology indicate that a
hydrologic connection was once present through a surface water connection to the river despite
the presence of a constructed berm, roadway, and trail between the two resources (DEA 2004).
The primary function of these wetlands is water quality improvement and hydrologic storage.
Railroad and recreational activities upslope make available pollutants that provide the
opportunity for water quality improvement. Wetlands A, C, D, and E are moderately vegetated
and have the ability to trap sediments.
Field observations indicate that Wetlands A, D, and E are inundated during the wet season and
dry during the summer months. Wetland C is inundated year round but has a significant area of
seasonal inundation. This characteristic facilitates the process of denitrification, which removes
nitrogen from the system by releasing it as Nitrogen gas. Wetlands A, C, D, and E have the
opportunity and potential to reduce concentrations of sediment, phosphorus, and nitrogen within
the waters that it receives.
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These wetlands have no surface water connection to the Green River and are hydrologically
isolated. Any stormwater flowing into them is trapped and does not contribute to downstream
flooding.
Wetland C provides wildlife habitat functions related to the complex vegetation structure, which
contains scrub/shrub and emergent vegetation. This type of vertical structure is a characteristic
that increases habitat complexity and niches (Hruby 2004). Additionally, Wetland C is in close
proximity to Wetland QR. These characteristics can provide appropriate habitat for wetland-
dependant and wetland-associated species and indicates greater opportunity for species dispersal
and foraging (Hruby 2004).
4.3 Wetland QR
Wetland QR is located between the BNSF and UPRR tracks. This almost 25-acre wetland spans
the distance between the UPRR and BNSF tracks for approximately 0.80 mile. This wetland is
characterized by a mature forested component dominated by cottonwood and a scrub/shrub
component dominated by willow species and red osier dogwood. The forested component
contains approximately 45,000 square feet of mature cottonwood stands along the east edge of
the UPRR track. Standing water and reed canarygrass along the railroad tracks comprise the
edges of Wetland QR.
Using the Ecology wetland rating system (Hruby 2004), Wetland QR scored as a Category II (i.e.
58 points). However, the mature forested component is a special characteristic of Wetland QR
that automatically makes that component a Category I wetland (Hruby 2004). The mature
forested portion is mostly black cottonwood (Populus trichocarpa) measuring 20 to 60 inches
diameter at breast height.
The scrub/shrub portion of Wetland QR is Category II. Therefore, following Ecology’s wetland
guidelines system (Hruby 2004), Wetland QR is a Category I/II wetland.
Wetland QR is connected to Wetland B by a 36-inch culvert under the UPRR tracks. Wetland B
is hydrologically connected to Wetland C. Wetland B is not impacted by this Project. A 36-inch
culvert at the north end of Wetland QR under the BNSF track connects Wetland QR to the
Springbrook Creek basin on the east.
This wetland provides water quality improvement, hydrologic storage, and wildlife habitat.
Railroad and recreational activities upslope make available pollutants that provide the
opportunity for water quality improvement. Wetland QR is a densely vegetated wetland that has
the ability to filter sediments, enhancing the ability to trap pollutants.
Wetland QR is inundated year round and has a significant area of seasonal inundation. This
characteristic facilitates the process of denitrification, which removes nitrogen from the system
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by releasing it as nitrogen gas. Wetland QR has the opportunity and potential to reduce
concentrations of sediment, phosphorus, and nitrogen within the waters that it receives.
Wetland QR provides wildlife habitat functions related to the complex vegetation structure,
which contains forested, scrub/shrub, and emergent vegetation. This type of vertical structure is
a characteristic that increases habitat complexity and niches (Hruby 2004). Additionally,
Wetland QR has a mature forested component. These characteristics can provide appropriate
habitat for wetland-dependant and wetland-associated species and indicates greater opportunity
for species dispersal and foraging (Hruby 2004).
4.4 Wetland T
Wetland T is a linear ditch feature located along the west edge of the BNSF track. The shape,
location, and concrete outlet structure indicate that the wetland was likely developed as part of a
stormwater management facility. Standing water was present throughout the wetland, as well as
a diverse number of emergent obligate wetland plants. The concrete outlet structure is
approximately 12 inches and is located under the BNSF track at the northern end of the project.
The primary function of this wetland is water quality improvement. Railroad, residential roads,
and recreational activities upslope make available pollutants that provide the opportunity for
water quality improvement. Wetland T is a densely vegetated wetland that has the ability to filter
sediments, enhancing the ability to trap pollutants.
Wetland T is inundated seasonally. This characteristic facilitates the process of denitrification,
which removes nitrogen from the system by releasing it as nitrogen gas. Wetland T has the
opportunity and potential to reduce concentrations of sediment, phosphorus, and nitrogen within
the waters that it receives.
Wetland T provides minimal wildlife habitat functions related to the emergent vegetation. This
characteristic can provide appropriate habitat for wetland-dependant and wetland-associated
species.
4.5 Mitigation Banking
It is anticipated that the direct wetland impacts of the Project will be mitigated for in the
Springbrook Creek Wetland and Habitat Mitigation Bank (Springbrook Bank), which is operated
and maintained by WSDOT and the City of Renton. The Springbrook Bank was established to
provide advanced compensatory mitigation for highway projects within the Lower Green and
Cedar River Basins (WRIA 8 an 9). The bank is located just east of the study area. See the
Mitigation Plan for more details (DEA 2007).
P:\p\PERT00000006\0600INFO\EP\EP37 Wetlands\Wetland Tech Memo\Strander Wetland Memo.doc
Wetland Technical Memorandum Page 7
Strander Boulevard Extension and Union Pacific Railroad Realignment Phase 1, Segments 2A and 2B
5.0 Summary
In summary, this technical memorandum complements the Wetlands Technical Discipline
Report, Strander Boulevard Extension (DEA 2004). The current project description includes the
UPRR relocation, an overpass of the UPRR and related stormwater facilities, and a bridge over
South Longacres Way.
The Project will impact nine wetlands for a total of 1.56 acres. The Project will also permanently
impact 3.09 acres of wetland buffer.
Using the Ecology rating system (Hruby 2004), all of the wetlands are Category III wetlands,
with the exception of Wetland QR which has a Category I/II rating. The Category I portion is a
one-acre stand of mature black cottonwood. The rest of the wetland, approximately 24 acres, is a
Category II.
We propose to mitigate for direct impacts to wetlands by using the Springbrook Bank. The
Springbrook Bank was established to provide advanced compensatory mitigation for highway
projects within the Lower Green and Cedar River Basins.
6.0 References
David Evans and Associates, Inc. (DEA). 2004.
———. 2007.
Hruby. 2004.
P:\p\PERT00000006\0600INFO\EP\EP37 Wetlands\Wetland Tech Memo\Strander Wetland Memo.doc
Wetland Technical Memorandum
Strander Boulevard Extension and Union Pacific Railroad Realignment Phase 1, Segments 2A and 2B
APPENDIX 1
VICINITY MAP
P:\p\PERT00000006\0600INFO\EP\EP37 Wetlands\Wetland Tech Memo\Strander Wetland Memo.doc
Wetland Technical Memorandum
Strander Boulevard Extension and Union Pacific Railroad Realignment Phase 1, Segments 2A and 2B
APPENDIX 2
WETLAND IMPACTS
P:\p\PERT00000006\0600INFO\EP\EP37 Wetlands\Wetland Tech Memo\Strander Wetland Memo.doc
Wetland Technical Memorandum
Strander Boulevard Extension and Union Pacific Railroad Realignment Phase 1, Segments 2A and 2B
APPENDIX 3
WETLAND RATING FORMS
P:\p\PERT00000006\0600INFO\EP\EP37 Wetlands\Wetland Tech Memo\Strander Wetland Memo.doc
Wetland Technical Memorandum
Strander Boulevard Extension and Union Pacific Railroad Realignment Phase 1, Segments 2A and 2B
APPENDIX 4
WETLAND PHOTOGRAPHS
Renton
Widener & Associates Transportation & Environmental Planning
10108 32nd Ave W, Suite D, Everett, WA 98204 Tel (425) 348-3059 Fax (425) 348-3124
Existing Outfall Conditions
TO: BergerABAM
FROM: Widener & Associates
SUBJECT: Stander Blvd Extension Project Outfall Inspection
DATE: 4/29/2016
This memo is provided to report on the existing conditions of two outfalls that have been identified as
potential outfall locations for the Strander Blvd Extension Project. The outfall is identified by the purple
line on the map ‘Strander Blvd Extension – Potential Outfall Locations’ (See attached), located just south
of the bridge on Strander Blvd that crosses the Green River. It is a corrugated metal outfall that is likely
below the vertical and horizontal limits of Ordinary High Water (Photo 1). Located at the bottom of a
steep bank, the outfall sits on angular rock that may have been added for bank stabilization. The outfall is
located roughly 80 feet southwest of a parking lot. The hillslope is mostly topped by sediment and
vegetation but subsurface conditions were not assessed during the visit. Vegetation at the site includes an
overstory of native trees with an invasive non-native understory which continues from the riverbank to
the parking lot.
Photo 1. Outfall identified by the purple alternative, adjacent to the bridge.
The outfall identified by the blue colored line in the ‘Potential Outfall Locations Map’, located to the
south, has been sealed off. It is located on the hillslope of the riverbank which has riprap armoring from
the river bank to roughly the elevation of the outfall (Photo 2). The outfall is roughly 25 feet downhill
from the roadway, where the slope begins to sharply descend to the water surface. Above the outfall, the
surface is mostly covered in sediment and herbaceous vegetation. A native overstory is present over a
mostly invasive non-native understory. Another small outfall (Photo 3), was found near the road edge.
The lack of scour beneath the outfall indicates that very little if any water is conveyed through this pipe.
Photo 2. Southern outfall identified by the blue line.
Photo 3. Small outfall found near the road, upslope from the southern outfall.
33301 9th Avenue South, Suite 300Federal Way, Washington 98003-2600(206) 431-2300 Fax: (206) 431-2250
STRANDER BLVD EXTENSION
POTENTIAL OUTFALL LOCATIONS
5-3-2016
1 of 1
PHASE 3 AREAS (5.47 ACRES)POND AREAS (2.37 TOTAL ACRES)PHASE 3 AREAS (7.84 TOTAL ACRES)
PHASE 3 AREAS (5.47 ACRES)POND AREAS (2.37 TOTAL ACRES)PHASE 3 AREAS (7.84 TOTAL ACRES)
PHASE 3 AREAS (5.47 ACRES)POND AREAS (2.37 TOTAL ACRES)PHASE 3 AREAS (7.84 TOTAL ACRES)
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24
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26
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27
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29
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R
B
R
I
D
G
E
2
EA
C
H
21
,
0
0
0
$
42
,
0
0
0
$
0
21
,
0
0
0
$
-
$
2 21,000.00 $ 42,000 $ 0 21,000.00 $ -$
32
FU
R
N
I
S
H
I
N
G
S
T
E
E
L
P
I
L
I
N
G
-
U
P
R
R
B
R
I
D
G
E
3,
9
9
0
LF
10
0
$
39
9
,
0
0
0
$
0
10
0
$
-
$
3990 100.00 $ 399,000 $ 0 100.00 $ -$
33
DR
I
V
I
N
G
S
T
E
E
L
P
I
L
I
N
G
-
U
P
R
R
B
R
I
D
G
E
42
EA
C
H
4,
0
0
0
$
16
8
,
0
0
0
$
0
4,
0
0
0
$
-
$
42 4,000.00 $ 168,000 $ 0 4,000.00 $ -$
34
FU
R
N
I
S
H
S
T
E
E
L
P
I
L
E
T
I
P
-
C
O
N
I
C
A
L
-
U
P
R
R
B
R
I
D
G
E
42
EA
C
H
2,
5
0
0
$
10
5
,
0
0
0
$
0
2,
5
0
0
$
-
$
42 2,500.00 $ 105,000 $ 0 2,500.00 $ -$
35
CO
N
C
R
E
T
E
C
L
A
S
S
4
0
0
0
-
U
P
R
R
B
R
I
D
G
E
1,
6
0
0
CY
50
0
$
80
0
,
0
0
0
$
0
50
0
$
-
$
1600 500.00 $ 800,000 $ 0 500.00 $ -$
36
RA
T
S
L
A
B
-
U
P
R
R
B
R
I
D
G
E
60
CY
25
0
$
15
,
0
0
0
$
0
25
0
$
-
$
60 250.00 $ 15,000 $ 0 250.00 $ -$
37
ST
E
E
L
R
E
I
N
F
O
R
C
E
M
E
N
T
-
U
P
R
R
B
R
I
D
G
E
40
0
,
0
0
0
LB
1.
0
0
$
40
0
,
0
0
0
$
0
1
$
-
$
400000 1.00 $ 400,000 $ 0 1.00 $ -$
38
DA
M
P
P
R
O
O
F
I
N
G
-
U
P
R
R
B
R
I
D
G
E
32
0
SY
75
$
24
,
0
0
0
$
0
75
$
-
$
320 75.00 $ 24,000 $ 0 75.00 $ -$
39
JO
I
N
T
W
A
T
E
R
P
R
O
O
F
I
N
G
-
U
P
R
R
B
R
I
D
G
E
26
0
LF
25
$
6,
5
0
0
$
0
25
$
-
$
260 25.00 $ 6,500 $ 0 25.00 $ -$
40
CL
E
A
N
I
N
G
A
N
D
P
A
I
N
T
I
N
G
-
U
P
R
R
B
R
I
D
G
E
1
LS
10
1
,
0
0
0
$
10
1
,
0
0
0
$
0
10
1
,
0
0
0
$
-
$
1 101,000.00 $ 101,000 $ 0 101,000.00 $ -$
41
PE
R
V
I
O
U
S
B
A
C
K
F
I
L
L
-
U
P
R
R
B
R
I
D
G
E
40
0
TO
N
20
$
8,
0
0
0
$
0
20
$
-
$
400 20.00 $ 8,000 $ 0 20.00 $ -$
42
SH
O
R
I
N
G
O
R
E
X
T
R
A
E
X
C
A
V
A
T
I
O
N
-
U
P
R
R
B
R
I
D
G
E
1
LS
42
9
,
0
0
0
$
42
9
,
0
0
0
$
0
42
9
,
0
0
0
$
-
$
1 429,000.00 $ 429,000 $ 0 429,000.00 $ -$
43
UP
R
R
S
H
O
O
F
L
Y
E
M
B
A
N
K
M
M
E
N
T
1
LS
59
6
,
0
0
0
$
59
6
,
0
0
0
$
0
59
6
,
0
0
0
$
-
$
1 596,000.00 $ 596,000 $ 0 596,000.00 $ -$
PH
A
S
E
I
I
I
T
O
T
A
L
Phase III
To
t
a
l
Ro
a
d
w
a
y
UPRR BNSF
N:
\
F
e
d
e
r
a
l
W
a
y
\
S
t
r
a
n
d
e
r
\
P
h
a
s
e
3
E
s
t
i
m
a
t
e
N
o
v
2
0
1
6
m
e
n
.
x
l
s
x
ST
R
A
N
D
E
R
B
O
U
L
E
V
A
R
D
P
R
O
J
E
C
T
C
O
S
T
E
S
T
I
M
A
T
E
PH
A
S
E
3
W
I
T
H
P
H
A
S
E
2
C
O
M
P
L
E
T
E
PR
O
J
E
C
T
C
O
S
T
L
I
N
E
I
T
E
M
To
t
a
l
Un
i
t
Un
i
t
C
o
s
t
Pr
i
c
e
Qu
a
n
t
i
t
y
Un
i
t
C
o
s
t
Pr
i
c
e
Quantity Unit Cost Price Quantity Unit Cost Price
PH
A
S
E
I
I
I
T
O
T
A
L
Phase III
To
t
a
l
Ro
a
d
w
a
y
UPRR BNSF
TR
A
I
L
B
R
I
D
G
E
Su
b
t
o
t
a
l
25
0
,
0
0
0
$
Su
b
t
o
t
a
l
Subtotal Subtotal
44
TR
A
I
L
B
R
I
D
G
E
1
LS
25
0
,
0
0
0
.
0
0
$
25
0
,
0
0
0
$
1
25
0
,
0
0
0
.
0
0
$
250,000
$
0 250,000.00 $ -$ 0 250,000.00 $ -$
LO
O
P
R
O
A
D
B
R
I
D
G
E
Su
b
t
o
t
a
l
99
0
,
0
0
0
$
Su
b
t
o
t
a
l
Subtotal Subtotal
45
LO
O
P
R
A
M
P
B
R
I
D
G
E
1
LS
99
0
,
0
0
0
.
0
0
$
99
0
,
0
0
0
$
1
99
0
,
0
0
0
.
0
0
$
990,000
$
0 990,000.00 $ -$ 0 990,000.00 $ -$
UT
I
L
I
T
Y
B
R
I
D
G
E
Su
b
t
o
t
a
l
30
0
,
0
0
0
$
Su
b
t
o
t
a
l
Subtotal Subtotal
46
UT
I
L
I
T
Y
B
R
I
D
G
E
1
LS
30
0
,
0
0
0
.
0
0
$
30
0
,
0
0
0
$
1
30
0
,
0
0
0
.
0
0
$
300,000
$
0 300,000.00 $ -$ 0 300,000.00 $ -$
UT
I
L
I
T
I
E
S
Su
b
t
o
t
a
l
1,
2
5
0
,
2
0
0
$
Su
b
t
o
t
a
l
Subtotal Subtotal
47
UT
I
L
I
T
I
E
S
-
M
I
S
C
1
LS
10
0
,
0
0
0
.
0
0
$
10
0
,
0
0
0
$
1
10
0
,
0
0
0
.
0
0
$
100,000
$
0 100,000.00 $ -$ 0 100,000.00 $ -$
48
SA
N
I
T
A
R
Y
S
E
W
E
R
R
E
-
R
O
U
T
E
1
LS
80
0
,
0
0
0
.
0
0
$
80
0
,
0
0
0
$
1
80
0
,
0
0
0
.
0
0
$
800,000
$
0 800,000.00 $ -$ 0 800,000.00 $ -$
49
F
I
B
E
R
O
P
T
I
C
R
E
L
O
C
A
T
I
O
N
1
LS
10
0
,
0
0
0
.
0
0
$
10
0
,
0
0
0
$
1
10
0
,
0
0
0
.
0
0
$
100,000
$
0 100,000.00 $ -$ 0 100,000.00 $ -$
50
CA
S
I
N
G
O
F
O
L
Y
M
P
I
C
/
B
P
F
U
E
L
L
I
N
E
S
A
T
U
P
R
R
60
LF
3,
9
2
0
.
0
0
$
23
5
,
2
0
0
$
60
3,
9
2
0
.
0
0
$
235,200
$
0 3,920.00 $ -$ 0 3,920.00 $ -$
51
SE
T
T
L
E
M
E
N
T
P
L
A
T
E
S
&
M
O
N
I
T
O
R
I
N
G
1
LS
15
,
0
0
0
.
0
0
$
15
,
0
0
0
$
1
15
,
0
0
0
.
0
0
$
15,000
$
0 15,000.00 $ -$ 0 15,000.00 $ -$
CI
V
I
L
Su
b
t
o
t
a
l
1,
8
4
2
,
4
0
4
$
Su
b
t
o
t
a
l
Subtotal Subtotal
52
HM
A
7,
6
7
8
TO
N
76
.
0
0
$
58
3
,
5
0
8
$
7,
6
7
8
76
.
0
0
$
583,508
$
0 76.00 $ -$ 0 76.00 $ -$
53
CS
B
C
5,
8
8
9
TO
N
30
.
0
0
$
17
6
,
6
6
7
$
5,
8
8
9
30
.
0
0
$
176,667
$
0 30.00 $ -$ 0 30.00 $ -$
54
GR
A
V
E
L
B
O
R
R
O
W
I
N
C
L
H
A
U
L
7,
4
2
1
CY
15
.
0
0
$
11
1
,
3
1
5
$
7,
4
2
1
15
.
0
0
$
111,315
$
0 15.00 $ -$ 0 15.00 $ -$
55
GR
A
V
E
L
B
O
R
R
O
W
I
N
C
L
H
A
U
L
R
O
A
D
W
A
Y
4,
2
4
3
TO
N
20
.
0
0
$
84
,
8
5
5
$
4,
2
4
3
20
.
0
0
$
84,855
$
0 20.00 $ -$ 0 20.00 $ -$
56
PE
R
M
E
A
B
L
E
B
A
L
L
A
S
T
3,
2
3
2
TO
N
60
.
0
0
$
19
3
,
8
9
1
$
3,
2
3
2
60
.
0
0
$
193,891
$
0 60.00 $ -$ 0 60.00 $ -$
57
SI
D
E
W
A
L
K
4,
0
2
7
SY
30
.
0
0
$
12
0
,
8
1
5
$
4,
0
2
7
30
.
0
0
$
120,815
$
0 30.00 $ -$ 0 30.00 $ -$
58
CU
R
B
&
G
U
T
T
E
R
5,
7
5
4
LF
70
.
0
0
$
40
2
,
7
8
0
$
5,
7
5
4
70
.
0
0
$
402,780
$
0 70.00 $ -$ 0 70.00 $ -$
59
DR
I
V
E
W
A
Y
E
N
T
R
A
N
C
E
10
5
SY
45
.
0
0
$
4,
7
3
0
$
10
5
45
.
0
0
$
4,730
$
0 45.00 $ -$ 0 45.00 $ -$
60
GR
A
V
E
L
37
7
TO
N
30
.
0
0
$
11
,
3
0
2
$
37
7
30
.
0
0
$
11,302
$
0 30.00 $ -$ 0 30.00 $ -$
61
UN
S
U
I
T
A
B
L
E
E
X
C
A
V
A
T
I
O
N
I
N
C
L
H
A
U
L
6,
9
3
4
CY
22
.
0
0
$
15
2
,
5
4
1
$
6,
9
3
4
22
.
0
0
$
152,541
$
0 22.00 $ -$ 0 22.00 $ -$
DR
A
I
N
A
G
E
Su
b
t
o
t
a
l
2,
5
7
7
,
0
0
0
$
Su
b
t
o
t
a
l
Subtotal Subtotal
62
UN
D
E
R
D
R
A
I
N
S
Y
S
T
E
M
1
LS
12
2
,
0
0
0
.
0
0
$
12
2
,
0
0
0
$
1
12
2
,
0
0
0
.
0
0
$
122,000
$
0 122,000.00 $ -$ 0 122,000.00 $ -$
63
ST
O
R
M
D
R
A
I
N
S
Y
S
T
E
M
1
LS
11
2
,
0
0
0
.
0
0
$
11
2
,
0
0
0
$
1
11
2
,
0
0
0
.
0
0
$
112,000
$
0 112,000.00 $ -$ 0 112,000.00 $ -$
64
TE
M
P
D
E
W
A
T
E
R
I
N
G
S
Y
S
T
E
M
1
LS
75
0
,
0
0
0
.
0
0
$
75
0
,
0
0
0
$
1
75
0
,
0
0
0
.
0
0
$
750,000
$
0 750,000.00 $ -$ 0 750,000.00 $ -$
65
ST
O
R
M
W
A
T
E
R
D
E
T
E
N
T
I
O
N
1
LS
87
,
0
0
0
.
0
0
$
87
,
0
0
0
$
1
87
,
0
0
0
.
0
0
$
87,000
$
0 87,000.00 $ -$ 0 87,000.00 $ -$
66
ST
O
R
M
W
A
T
E
R
W
E
T
L
A
N
D
1
LS
12
0
,
0
0
0
.
0
0
$
12
0
,
0
0
0
$
1
12
0
,
0
0
0
.
0
0
$
120,000
$
0 120,000.00 $ -$ 0 120,000.00 $ -$
67
OU
T
F
A
L
L
T
O
R
I
V
E
R
1
LS
23
6
,
0
0
0
.
0
0
$
23
6
,
0
0
0
$
1
23
6
,
0
0
0
.
0
0
$
236,000
$
0 236,000.00 $ -$ 0 236,000.00 $ -$
68
PS
-
U
P
P
U
M
P
S
T
A
T
I
O
N
1
LS
75
0
,
0
0
0
.
0
0
$
75
0
,
0
0
0
$
1
75
0
,
0
0
0
.
0
0
$
750,000
$
0 750,000.00 $ -$ 0 750,000.00 $ -$
69
PS
-
G
W
U
P
G
R
A
D
E
P
U
M
P
S
T
A
T
I
O
N
1
LS
40
0
,
0
0
0
.
0
0
$
40
0
,
0
0
0
$
1
40
0
,
0
0
0
.
0
0
$
400,000
$
0 400,000.00 $ -$ 0 400,000.00 $ -$
MI
S
C
Su
b
t
o
t
a
l
1,
3
7
0
,
5
9
2
$
Su
b
t
o
t
a
l
Subtotal Subtotal
70
QU
A
R
R
Y
S
P
A
L
L
S
F
O
R
S
I
T
E
A
C
C
E
S
S
6,
8
2
4
TO
N
S
25
.
0
0
$
17
0
,
5
9
2
$
68
2
4
25
.
0
0
$
170,592
$
0 25.00 $ -$ 0 25.00 $ -$
71
TR
A
F
F
I
C
S
I
G
N
A
L
3
EA
15
0
,
0
0
0
.
0
0
$
45
0
,
0
0
0
$
3
15
0
,
0
0
0
.
0
0
$
450,000
$
0 150,000.00 $ -$ 0 150,000.00 $ -$
72
ER
O
S
I
O
N
C
O
N
T
R
O
L
A
N
D
P
L
A
N
T
I
N
G
1
LS
20
0
,
0
0
0
.
0
0
$
20
0
,
0
0
0
$
1
20
0
,
0
0
0
.
0
0
$
200,000
$
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3/16/2017
1
INTRODUCTION
The following document is an outline of assumptions used to develop the Conceptual Plan Cost Estimate
for full build out of the Strander Grade Separation, including the proposed extension under UPRR,
widening of previously constructed Phase 2 and construction of a watertight seal for the entire length of
the project. Because plans for the proposed Phase 3 have not yet been prepared, the estimate is based
on AutoCAD modeling, preliminary calculations of the thickness of the bottom seal and some sketches
located in the cost estimate folder along with the cost estimating spreadsheet. The basic configuration
of the proposed project is shown in Image 1.
MAINTENANCE OF TRAFFIC
To construct the UPRR and BNSF bridge foundations and the seal across the entire roadway, the road
will need to be closed for construction. The sounder station will still be accessible from West Valley and
Longacres Way.
WALLS AND BOTTOM SEAL (see Images 2 and 2a)
The walls for the boat are constructed with sheet piles with a permanent concrete wall cast in front of
the sheet piles. The sheet piles are supported with tie backs and an anchor wall as a temporary
condition to excavate and place the seal. The permanent concrete wall is 2’ thick and poured
monolithically with a reinforced footing layer that sits on top of the seal. The roadway section is built on
top of this footing layer.
Lean, unreinforced concrete will be used for the bottom seal. There are two ways to construct the seal.
The first (used for this estimate) is to excavate and place the seal with minimal dewatering. Contractor
will have to use methodology similar to dredging. This simplifies the dewatering process during seal
construction but complicates the contractor’s means and methods. The second way to construct the
seal includes dewatering below or near the bottom of seal. There were challenges during Strander Phase
2 construction on where to discharge this water, therefore we are not proposing this at this time,
however it is possible and needs to be evaluated during design.
Temporary dewatering is pumped north to Renton’s storm sewer like was done for beginning of phase
2. Temporary dewatering will be required to construct the structural walls, footing layer and roadway
section.
The cost for removal of structure and obstructions for seal is assumed to be 5% of bottom seal.
The foundations for the Bridges (Except pedestrian bridge) are part of the boat seal foundation, but are
constructed differently. Dewatering to the bottom of the seal is required at the UPRR, BNSF and
Vehicular bridges. The new BNSF, UPRR and Vehicular bridges will have same pile layout and seal as
BNSF Phase II Bridge. At these locations the sheet pile walls have to step behind the foundations, so that
the finished wall alignment matches between the structures and the structural walls. 6” rat slab under
UPRR and BNSF bridge foundations.
The sheet pile walls wrap the entire project to excavate for the seal, see images 3 and 3a for wall
locations. Sheet piles are assumed to be imbedded 50% of exposed face. We assumed PZ40 section for
the sheets. Where a seal is not required these sheets and the structural wall maybe replaced with other
wall types (Modular block wall 10’ long by up to 6’ tall).
3/16/2017
2
Anchor wall will be constructed continuously to support the sheet pile wall while seal is excavated and
poured, see images 3 and 3a. The anchor wall will be 8’ tall 16” thick cast-in-place concrete. There is an
option to use two sheet piles at each tie rod. This alternative may be cheaper (to be evaluated in
design). Excavation is incidental to bid item.
Tie rods are 70’ long from face of sheet pile wall to back of anchor wall. One layer of tiebacks across all
sheet pile walls at 9.2’ OC w/ waler (waler is assumed to be two MC10x22’s). The waler will be placed in
front of the sheet pile wall and cast into the permanent structural concrete wall. Construction of this
around the UPRR bridge and loop ramp will have to coincide with shoofly design of UPRR tracks.
Permanent ground anchors maybe a better option at this location and also around the restaurant
establishments. The utility corridor on the north side of the project also needs to be vetted with the
anchor wall design, see image 3a.
PHASE 2 WIDENING & RECONSTRUCTION (See image 4)
The cast in place retaining walls founded on pile supported spread footings are assumed to be removed
as part of this project. This is based on integrating the seal with the structural walls and the complication
of tying into the pile supported spread footings. This should be evaluated further in design.
The ecology block wall on the SE side of the BNSF Bridge will be removed as part of this project.
Quarry spalls are located on the slopes around the low part of phase 2 construction (between ramp to
sounder station and the BNSF Bridge). These may be salvageable but was not the basis for the cost
estimate.
Demo of Strander Phase II items is a $200,000 LS item. This includes roadway section, walls, quarry
spalls, sidewalk and other phase 2 items to be removed.
Pump station will be updated, a second series of pumps will be added, and the pond will be modified to
include a detention pond and storm wetland. An outfall will be constructed out to the river. Additional
items included in cost estimate to update and modify the drainage and storm systems are identified in
the drainage report memo. There will be two series of drains in the boat. The first will use catch basins
to capture the storm and pumped through the new pumps to the detention pond. The second series of
drains will utilize an underdrain system on top of the seal to capture ground water that gets into the
boat. This will be pumped through the upgraded pump system to the storm wetland (WQ Wet). An
outfall will go from the WQ Wet pond to the river and will include boring under UPRR and West Valley
HWY and new pipe connecting the system. See drainage report memo and Figure 32 (from drainage
report) for preferred drainage alternative detail. This figure shows groundwater being routed through
the water quality feature. However, it may be sent directly to the river.
3/16/2017
3
STORM WATER SYSTEM & UNDERDRAIN
Underdrain system of (2)12” perforated pipe longitudinally under the road with 6” perforated pipe
transversely at 10’ OC. Catch basins were not included in the cost but assumed the underdrain system
was overdesigned enough to capture these costs
BNSF/UPRR BRIDGES
The bridge constructed during phase 2 can accommodate 3 tracks. It is assumed the foundations for a
4th track will be constructed as part of phase 3. The superstructure will not be constructed as part of this
project. Existing concrete retaining walls are assumed to be removed as part of this work. The sheet pile
wall required behind the abutment was installed in phase 2. Temporary structural shoring will be
required across the roadway cross section to build the pile supported foundation, See image 5.
3/16/2017
4
The interface between the BNSF bridge abutments and the structural walls for the boat (sheet pile and
reinforced concrete wall) may have gaps that need to be resolved in design.
The shoofly is to the east of the existing UPRR rail alignment. The UPRR Bridge may be constructed in
one sequence, see images 6-8.
The structural shoring walls and permanent boat walls are interconnected and each has been broken
out in the cost estimate. The anchor walls and tie rods to accommodate excavation of the boat seal are
complicated due to staging of the UPRR bridge construction, the vehicular bridge ramp, the overhead
power utilities and the pedestrian bridge, see image 2.
Construction of the UPRR and BNSF bridges are assumed to be identical to the phase 2 construction and
phasing of the BNSF Bridge.
PEDESTRIAN, UTILITY AND VEHICULAR BRIDGES
All of these bridges are based on price per square foot.
Structural shoring will be required for each of these bridges but is incidental to the per square foot
bridge cost used.
The pedestrian bridge is assumed to be a prefabricated superstructure supported on cast-in-place
foundations. The foundations are located behind the structural walls for the boat and may be pile
supported, see image 9
The vehicular bridge is assumed to be a precast concrete girder superstructure on a pile supported
foundation similar to the BNSF Bridge without a middle pier, see image 10.
Utility bridge was left in the estimate. It is uncertain if it will be needed
ROW (See image 11 and 11a)
It has been assumed we can get an easement for the tiebacks so the anchor wall can be installed. Tie
rods might need to be cut before project completion.
ROW and easement coordination still needs to be accomplished.
MISCELLANEOUS ITEMS AND UTILITIES
Fences are needed behind each sheet pile wall and modular block wall.
Assumed unsuitable excavation of 3’ under road only where there is no seal due to seal being able to
accommodate unstable material.
Quarry spalls for construction access assumed to be 3’ thick in all new construction areas. Phase 2 areas
are not included because they already have a 3’ quarry spall over excavation with quarry spalls, see
Image 12.
Erosion Control was estimated as $200,000, based on experience at Strander Phase 2.
Landscaping was estimated as $50,000, based on experience from other projects.
Lighting was estimated as $200,000, based on experience from other projects.
3/16/2017
5
Taco Bell and Jack in the Box parking lot improvements estimated as $40,000 each. Jack in the box is not
needing relocating. Retaining walls will be required for both of these companies to maintain the drive
through access. The design needs to be coordinated with the owners. Taco bell may need to be
relocated and is estimated to cost $1,000,000.
The Olympic BP petroleum gas lines (2) run on the North side of the project, behind the BNSF and UPRR
bridges until they reach the shared use path on the west side of the project. Then they turn south and
cross the footprint of the project. The depth of the seal is below these lines and they will need to be
relocated. The Olympic BP relocation costs $1,000,000 is based on a telephone conversation with BP. BP
stressed that this was very much a guess. They also requested a long lead time to coordinate this work,
see images 13 and 13a.
Casing of the Olympic BP gas line will be required under the shoofly.
Sewer was estimated to be relocated at a cost of $800,000 and an additional $300,000 for a utility
bridge where it crosses the boat section. See the VE study.
Localized distribution and transmission lines (lines on the small poles) may have to be temporarily or
permanently relocated. This was estimated at $100,000 lump sum. The high mast transmission is
assumed to remain; coordination with bridge construction required, see images 13 and 13a
$100,000 lump sum was used for the fiber relocation. This value was based on Phase 2.
Costs to work with UPRR are similar to BNSF from phase 2.
REINFORCEMENT
Reinforcing for structural elements are based on standard volumetric ratios:
- For the concrete seal walls and bottom, reinforcing is estimated at 300lbs/CY of Concrete
- BNSF Bridge, reinforcing is estimated at 250lbs /CY of concrete
- UPRR Bridge, reinforcing is estimated at 250lbs /CY of concrete
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Image 3 - West Side Plan w/ ROW and Utilities
Sheet Pile & Structural Wall
Structural Foundations (Pile Supported)
Approximate Seal Limits (Depth Varies)
Anchor Wall
Tie Back Rod (or PGA)
Image 3a - East Side Plan w/ ROW and Utilities
Sheet Pile & Structural Wall
Structural Foundations (Pile Supported)
Approximate Seal Limits (Depth Varies)
Anchor Wall
Tie Back Rod (or PGA)
Utility Corridor
Image 4 - Phase 2 Materials to Be removed/Reused
Quarry Spalls Material Left-in-place
Phase 2 Construction
Ecology Block Wall (To Be Remove)
Walls on Pile Supported Footings (To
Be Removed)
Pump Station (To Be Updated and
Expanded)
Pond (To Be reconfigured - See
Drainage Memo)
BNSF Bridge
BNSF 4th Track Substructure
Imag
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5
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See Image11a for Key
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