HomeMy WebLinkAboutUtilities 2012-09-25 Item 2C - Review - Surface Water Comprehensive Plan / Capital Improvement ProgramCity of Tukwila
Jim Haggerton, Mayor
TO: Mayor Haggerton
Utilities Committee
FROM: Bob Giberson, Public Works Director-
BY: Ryan Larson, Senior Engineer
DATE: September 21, 2012
SUBJECT: Surface Water Comprehensive Plan
Project No. 91041202
Draft Comprehensive Plan for Review Capital Improvement Projects
ISSUE
Present draft of the proposed 2012 Surface Water Comprehensive Plan and review the proposed
Capital Improvement Projects.
BACKGROUND
The City hired CH2M Hill to update our Surface Water Comprehensive Plan (SWCP) to reflect changes
in regulatory requirements and drainage needs within the City. The current SWCP was completed in
2003 and does not reflect changes in regulations required under the City's National Pollutant Discharge
Elimination System Permit, our current GIS inventory, completed CIP projects, the Tukwila South
annexation area, nor newly identified needs.
DISCUSSION
Staff intends to review the draft SWCP in a series of three Utilities Committee meetings. This first review
will concentrate on how the project lists were determined and the corresponding proposed CIP projects.
The second meeting will review the entire SWCP document. Staff will then complete a final draft, obtain a
SEPA determination, and bring the SWCP forward for final review and Council approval by resolution.
The primary purpose of the SWCP is to review surface water and habitat needs and develop a list of
proposed CIP projects. The proposed projects are developed by reviewing past project lists, interviewing
staff, reviewing citizen complaints, and performing field assessments. Past projects that are no longer
needed are removed, existing projects costs are updated, and new projects are added to comply with
changes in regulations and newly identified deficiencies. A total of 14 Capital projects are proposed in
the SWCP under the 412 Fund and 4 are proposed under the 301 Fund that are related to fish habitat
improvements. Proposed new projects in the 412 Surface Water fund include:
Water Quality Retrofit Program East Marginal Way Conveyance Inspections
Tukwila Pkwy /Gilliam Creek, outfalls Tukwila Urban Center Conveyance Inspections
There are not any new fish habitat projects proposed.
RECOMMENDATION
Information only.
Attachments: CIP Pages 137, 140, 147, 149, 156
Surface Water Comprehensive Plan Chapter 4 and 5
Draft Surface Water Comprehensive Plan Under Separate Cover
W'\PW Eng1PROJECTSW- DR Projects%Surface Water Comp Plan (91041202) \Info Memo Draft Plan for Review CIP gl docx
10
City of Tukwila
CAPITAL IMPROVEMENT PROGRAM
for
2013-2018
IMINN
CIP
"Other
After Six
Page
PROJECT TITLE
2013
2014
2015
2016
2017
2018
TOTAL
Sources
Years
138
Annual Small Drainage Program
645
685
685
685
685
685
4,070
273
685
139
NPDES Program
150
155
155
160
160
160
940
0
160
140
Water Quality Retrofit Program
110
110
110
110
110
110
660
0
110
141
GIS Inventory
15
15
15
15
15
15
90
0
15
142
Storm Lift Station No. 15 Improvements
585
0
0
0
0
0
585
0
0
143
Soils Reclamation Facility
311
2,543
0
0
0
0
2,854
2,800
0
144
East Marginal Wy S Stormwater Outfalls
120
0
251
785
0
0
1,156
0
0
145
Christensen Rd Pipe Replacement
61
266
0
0
0
0
327
0
0
146
Gilliam Creek 42 Ave S Culvert
25
600
0
0
0
0
625
0
0
147
E Marginal Wy Conveyance Inspection
0
85
0
0
0
0
85
0
0
148
53rd Ave S Storm Drain System
0
0
0
0
293
1,264
1,557
0
0
149
Tukwila Pkwy /Gilliam Creek Outfalls
0
0
0
0
0
230
230
0
0
150
S 146th St Pipe 35th Ave S Drainage
0
0
0
0
0
0
0
0
882
151
S 143rd Street Storm Drain System
0
0
0
0
0
0
0
0
1,096
152
Nelsen PI /Longacres Phase II
0
0
0
0
0
0
0
0
345
153
Northwest Gilliam Storm Drainage System
0
0
0
0
0
0
0
0
940
154
Duwamish Rvrbk Stabilization at S 104th St
0
0
0
0
0
0
0
0
595
155
Surface Water Comprehensive Plan
0
0
0
0
0
0
0
0
175
156
TUC Conveyance Inspection
0
0
0
0
0
0
0
0
541
Grand Total
2,022
4,459
1,216
1,755
1,263
2,464
13,179
3,073
5,544
Denotes other funding sources, grants, or mitigation.
Chanoes from 2012 to 2013 CIP:
Additions
140 Water Quality Retrofit Program
147 E Marginal Wy Conveyance Inspection
149 Tukwila Pkwy /Gilliam Creek Outfalls
156 Tukwila Urban Center Conveyance Inspection
Deletions
Private Storm System Adoption, most completed, remainder will be added to Small Drainage Program.
Andover Park W 48 -inch Drain Rehabilitation, combined with Tukwila Pkwy /Gilliam Creek Outfalls
Property for Riverton Creek Sediment Trap, minimal benefit with high costs; cannot justify project.
Duwamish Riverbank Stabilization near S 115th St, responsibility of KCFCZD.
Minkler Blvd Culvert Replacement, no longer needed due to new development at SC Pkwy /Strander Blvd.
Treatment Pond for Gilliam Creek, minimal benefit with high costs; cannot justify project.
Retrofit Storm Water Treatment at 51 st Ave S, minimal benefit with high costs; cannot justify project.
Tukwila Parkway Drainage, minimal benefit with high costs; cannot justify project.
Lift Station No. 15
Lift Station No. 16
Lift Station No. 17
Lift Station No. 18
Lift Station No. 19
5880 S 180th St Claim Jumper
7420 S 180th St (underpass)
530 Strander Blvd Bicentennial Park
4225 S 122nd St Allentown
Fort Dent Park (Parks Dept.)
137
11
CITY OF TUKWILA CAPITAL PROJECT SUMMARY
2013 to 2018
PROJECT: Water Quality Retrofit Program Project No. 91241202
DESCRIPTION: Design and install water quality vaults at selected locations throughout the City
JUSTIFICATION: NPDES permit requirements to improve water quality.
STATUS: New project for 2013 2018 CIP. Two candidates have been identified; water quality vaults (WOV)
for 48th Ave S and S 122nd St.
MAINT. IMPACT: Expected to increase maintenance.
COMMENT: Combine with other CIP projects for design and construction, where feasible
FINANCIAL Through Estimated
(in $000's)
2011 2012 2013
2014
2015
2016
2017
2018
BEYOND
TOTAL
EXPENSES
Design
15
15
15
15
15
15
15
105
Land (RAM
0
Const. Mgmt.
15
15
15
15
15
15
15
105
Construction
80
80
80
80
80
80
80
560
TOTAL EXPENSES
0 0 110
110
110
110
110
110
110
770
FUND SOURCES
Awarded Grant 0
Proposed Grant 0
Mitigation Actual 0
Mitigation Expected 0
Utility Revenue 0 0 110 110 110 110 110 110 110 770
TOTAL SOURCES 0 0 110 110 110 110 110 110 110 770
T1
Project Location:
E ntire Syst
r
5
y�
i
e
2013 2018 Capital Improvement Program
140
GIs'
im
12
FUND SOURCES
Awarded Grant 0
Proposed Grant 0
Mitigation Actual 0
Mitigation Expected 0
Utility Revenue 0 0 0 85 0 0 0 0 0 85
TOTAL SOURCES 0 0 0 85 0 0 0 0 0 85
147
S 1 2.1906 ,%128
Ip
G
13
A I r a to) "A'A I W- I
STATUS:
MAINT. IMPACT: After project completion, maintenance will be able to clean and inspect the pipes.
COMMENT: New manhole structures will include the slide gates which will control water flow during maintenance.
Through Estimated
2011 2012 2013 2014 2015 2016 2017 2018 BEYOND TOTAL
30 30
0
25 25
175 175
0 0 0 0 0 0 0 230 0 230
0
0
0
0
0 0 0 0 0 0 0 230 0 230
0 0 0 0 0 0 0 230 0 230
.-.t Location
'S
is on
L
S N
1
Pw
1 a...
eT
ir
J�IS
J
2013 2018 Capital Improvement Program
1z' L41
14
CITY OF TUKWILA CAPITAL PROJECT SUMMARY
2013 to 2018
PROJECT: Tukwila Urban Center Conveyance Inspections Project No. 91241203
DESCRIPTION: Clean and inspect existing piped conveyance systems 30" or larger throughout the Tukwila Urban Center
ProjectLocation 8 13681
A
T
s
Ile
GS
2013 2018 Capital Improvement Program 156
15
4.0 Surface Water Issues and Solutions
This section summarizes existing surface water issues. These issues are organized by type of
surface water issue: drainage, water quality, or aquatic habitat. Appendix D contains the
detailed information in support of this Section 4.
4.1 Available Data and Information
The following sources of information were used to identify drainage, water quality, and
aquatic habitat issues:
Anecdotal and recorded information provided by City staff
Observations made during field visits by CH2M HILL and City staff
2003 City of Tukwila Comprehensive Surface Water Management Plan
The following drainage studies:
1993 Surface Water Management Comprehensive Plan
1994 Gilliam Creek Detention and Water Quality Enhancements
1996 Fostoria Basin Stormwater Quality Management Plan
1997 Southgate Creek By -Pass Study
2001 Gilliam Creek Basin Storm Water Management Plan.
4.2 Identified Surface Water Issues
Localized drainage problems are the primary surface water concern for the residents of the
City of Tukwila. Drainage issues arise on both public and private property because there are
no storm drainage systems, the existing conveyance systems are damaged or in need of
maintenance, or the existing conveyance systems have inadequate hydraulic capacity. Much
of the development in Tukwila occurred previous to current stormwater flow control
standards. In addition, as impervious surfaces are added, more stormwater runs off during
storms, exacerbating existing problems.
Water quality problems are evident in the Green and Duwamish River system and in each
of the major creek systems within the City of Tukwila. The Green River and Duwamish
River are listed as impaired on the 2008 Ecology 303(d) list for dissolved oxygen,
temperature, pH, and fecal coliform. Untreated runoff from arterial streets with intensive
traffic usage, areas of dense commercial development, parking lots in the Tukwila
International Boulevard corridor and Westfield Mall area, and I -5 and I-405 contributes to
these problems. All of Tukwila s creek systems are affected, including Gilliam, Riverton,
Southgate, and Johnson Creeks. Runoff conveyed to the river via these creeks is contributing
to the impaired water quality of the Green and Duwamish Rivers.
Available aquatic habitat has been significantly reduced in the creeks that drain Tukwila
due to the effects of development and the loss of riparian buffer areas. Uncontrolled runoff
4.1
16
CITY OF TUKWILA 2012 SURFACE WATER COMPREHENSIVE PLAN
flows coupled with steep slopes in the upper reaches of Gilliam, Southgate, Riverton, and
Johnson Creeks cause channel erosion that in turn delivers sediments to the lower gradient
downstream reaches of these streams. Sediment deposition significantly reduces the
conveyance capacity of these channels, restricts fish passage, and hinders the potential for
salmonid spawning in these lower reaches. Better quality aquatic habitat in the lower
reaches of all four streams in Tukwila would provide refuge to salmonids from high flows
and predators in the Green and Duwamish Rivers. Several culverts are blockages to fish
passage from the lower reaches to the upper reaches of each of the creek systems.
Addressing these blockages to fish passage would provide salmonids access to aquatic
habitat in the upper reaches of these systems. In addition, restoration of riparian buffer
areas both in the upper and lower reaches of these creeks would reduce water temperatures,
which is better for salmonids at all life cycles.
Table 4 presents a summary of the number of identified drainage, water quality, and aquatic
habitat issues. Individual surface water issues are shown on Figure 6 and discussed in detail
in Appendix D.
TABLE 4
Surface Water Issue Summary
This Comprehensive Surface Water Management Plan for Tukwila has outlined 26 specific
surface water problems within the City of Tukwila. In addition to these specific 26, several
smaller drainage issues have been identified by the City of Tukwila and have been included
on the Small Drainage Project List maintained and frequently updated by City of Tukwila
staff. The drainage issues on the Small Drainage Project List are addressed as a small
drainage program.
4-2 WBG031611103411SEAtSURFACEWATERCOMPP LAN_DRAFT2012_0831-REV
17
Type of Surface Water Issue
Number
Water
Aquatic
Drainage Basin
of Issues
Drainage
Quality
Habitat
Green/ Duwamish
9
X
X
X
Gilliam Creek
5
X
X
Nelson Place Long Acres
3
X
X
X
P17
1
X
Riverton Creek
3
X
X
Southeast CBD
0
Southgate Creek
3
X
X
Johnson Creek
0
City -wide
2
X
X
Totals
26
X
X
X
This Comprehensive Surface Water Management Plan for Tukwila has outlined 26 specific
surface water problems within the City of Tukwila. In addition to these specific 26, several
smaller drainage issues have been identified by the City of Tukwila and have been included
on the Small Drainage Project List maintained and frequently updated by City of Tukwila
staff. The drainage issues on the Small Drainage Project List are addressed as a small
drainage program.
4-2 WBG031611103411SEAtSURFACEWATERCOMPP LAN_DRAFT2012_0831-REV
17
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4.
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uft w
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Lake `singtn
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0
a
Surface Water Issues City of Tukwila Stormwater Pipe
Drainage King County Unincorporated Drainage Basins
Drainage /Habitat Other Municipalities A Outfall
Habitat
4
I
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y
a
a n°is f
I
N
18
6
Lake `singtn
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0
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Surface Water Issues City of Tukwila Stormwater Pipe
Drainage King County Unincorporated Drainage Basins
Drainage /Habitat Other Municipalities A Outfall
Habitat
4
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a
a n°is f
I
N
18
CITY OF TUKWILA 2012 SURFACE WATER COMPREHENSIVE PLAN
4.3 Menu of Solutions to Address Surface Water Issues
This section outlines the menu of solutions that could be used to address the surface water
issues identified in the City of Tukwila. No single type of action, activity, or project is a "one
size fits all" fix to all of these identified problems. Some surface water problems have
structural solutions, while others have programmatic (non structural) solutions, and many
have both programmatic and structural solutions. Implementing a diverse portfolio of
solutions allows for different aspects of the issues to be addressed by different solutions.
Potential solutions are divided into actions that would not involve construction or land
acquisition, collectively referred to as programmatic approaches, and actions that would
require capital projects and would be listed in the City of Tukwila Capital Improvement
Program. The programmatic activities have the benefit of often being strategic rather than
reactionary. Instead of fixing a single problem with a structural solution, programmatic
alternatives often address a series of existing problems and are effective at preventing future
problems.
Often, capital (structural) solutions are most effective for single- location surface water
problems and programmatic solutions are most effective for watershed -wide or other large
scale problems. Regulatory requirements (such as the NPDES Phase II permit) emphasize
programmatic approaches to problems. Also, water quality problems can be targeted
successfully using programmatic means such as source control measures. Sub basin- or
watershed -wide water quantity problems, such as increase in impervious surface runoff, can
be addressed with programmatic solutions. Location- specific habitat, water quality, and
water quantity issues can be addressed with capital projects. Using capital projects and
programmatic solutions in tandem is the most effective method of addressing drainage,
water quality, and aquatic habitat problems comprehensively.
Because multiple sources contribute to the problems, multiple solutions targeting different
sources and different aspects of sources are appropriate. Programmatic actions can provide
overlapping benefits, thus addressing several pollution sources at once. However, capital
projects can yield immediate, measurable results in a specific location, such as reduction of
sediment load to the Green River from a specific parking lot. An additional benefit of capital
projects is that the City can implement any number of individual capital projects in any
given year depending upon funding availability.
Both capital and programmatic solutions are discussed in the next sub sections.
4.3.1 Programmatic Solutions
The driving factor behind the comprehensive stormwater management plan is to
comprehensively address drainage, water quality, and aquatic habitat issues identified in
the City of Tukwila. The type(s) of surface water issues that could be addressed by
individual programmatic solutions are summarized in Table 5. Note that many of these
activities are required in whole or in part by the City's NPDES Phase II permit. The
remainder of this sub section discusses each of seven programmatic solutions in further
detail. These seven types of programmatic solutions are education, incentives, changes to
City policies or regulations, inspections and enforcement, illicit discharge detection and
elimination, public involvement and compliant response, and operations and maintenance.
19
4.0 SURFACE WATER ISSUES AND SOLUTIONS
TABLE 5
Surface Water Issue Types Addressed by Programmatic Solutions
4.3.1.1 Education
Many surface water issues in Tukwila are caused by the everyday actions of people that live
in or visit the City. While difficult, changing behavior patterns is a cost effective
programmatic solution to surface water problems. Establishing public knowledge of the link
between activities within the watershed and ecosystem health is imperative for the success
of these education programs.
The educational topics listed below would supplement the current City of Tukwila
education program:
Surface water runoff from existing residential lots
Surface water runoff from new developments
Improperly maintained surface water detention or treatment facilities
Proper maintenance of septic systems (where applicable)
Wastewater conveyance systems inspection and maintenance
Dog and cat pet waste disposal
Erosion management
Wildlife
Waterfowl (ducks and geese)
General awareness of receiving water health and fostering `ownership'
Education has drainage, water quality, and aquatic habitat benefits.
WBG031 61 1 1 034 1 1SEAiSURFACEWATERCOMPPLAN _DRAFT2012_0831_REV 4 -5
20
Surface Water Issue Type
Required (in whole
or in part) by
Water
Aquatic
NPDES Phase II
Program Element
Drainage
Quality
Habitat
Permit
Education
x
x
x
x
Incentives
x
x
x
Changes to City
x
x
x
Policies or Regulations
Inspections and
x
x
x
Enforcement
Illicit Discharge
x
x
Detection and
Elimination
Public Involvement
x
x
x
x
(including complaint
response)
Operations and
x
x
x
x
Maintenance
4.3.1.1 Education
Many surface water issues in Tukwila are caused by the everyday actions of people that live
in or visit the City. While difficult, changing behavior patterns is a cost effective
programmatic solution to surface water problems. Establishing public knowledge of the link
between activities within the watershed and ecosystem health is imperative for the success
of these education programs.
The educational topics listed below would supplement the current City of Tukwila
education program:
Surface water runoff from existing residential lots
Surface water runoff from new developments
Improperly maintained surface water detention or treatment facilities
Proper maintenance of septic systems (where applicable)
Wastewater conveyance systems inspection and maintenance
Dog and cat pet waste disposal
Erosion management
Wildlife
Waterfowl (ducks and geese)
General awareness of receiving water health and fostering `ownership'
Education has drainage, water quality, and aquatic habitat benefits.
WBG031 61 1 1 034 1 1SEAiSURFACEWATERCOMPPLAN _DRAFT2012_0831_REV 4 -5
20
CITY OF TUKWILA 2012 SURFACE WATER COMPREHENSIVE PLAN
4.3.1.2 Incentives
Incentives could be considered as a way to more quickly and more effectively obtain the
targeted benefits of education. Incentives are one step over on the education- incentives-
regulations- enforcement spectrum.
Incentives are most often financial. Possible incentives include:
Free "mutt mitts" for pet owners
Reduced surface water fee with on -site surface water management implemented on
private property
Free technical assistance for private property owners wishing to implement on -site
surface water management (such as rain gardens or rain barrels)
Incentives would have drainage, water quality, and aquatic habitat benefits.
4.3.1.3 Regulatory and Policy Changes
Most existing drainage problems are best addressed with a capital project. However,
programmatic solutions can be used to prevent future drainage problems by managing how
new and re- development is conducted.
Most of the water quality problems in Tukwila are caused by the activities of residents and
visitors, including the way that people use the land. These pollutants cannot be removed
practically by stormwater treatment facilities that are typically more effective at removal of
point source pollution. Therefore, protection of water quality is dependent on improved
regulations to address the source of the pollutants.
Possible changes to City policies or regulations include the following:
Require maximum potential infiltration on development and re- development sites
Require zero stormwater discharge from all new development
Establish a policy of no net increase in Effective Impervious Area in the City
Establish a policy of no net loss of forest cover in the City
Require annual inspections and corrections for septic systems (where applicable)
Require that all new roads, driveways, parking areas and walkways be constructed of
pervious materials such as pervious asphalt, concrete, or pavers
Changes to policies or to regulations at the state or national level are outside the scope of
this Plan.
Changes to City policies and regulations would have drainage, water quality, and aquatic
habitat benefits.
4.3.1.4 Inspection and Enforcement
Inspections are conducted during construction activities to ensure compliance with existing
requirements. In Tukwila, these inspections might occur at less than-ideal frequency due to
4 -5
21
LrI�� 'J����Il� ^Irsltlrl.�[illttiG 7�3
lack of available personnel. In addition, enforcement is difficult. The inspection program
would be enhanced and a more reliable and detailed recording system should be utilized.
This recording system should be used to determine "hot spots" or "repeat offenders."
Programmatic decisions affecting inspection and enforcement would incorporate input from
the City's Planning and Development Services department.
In addition to inspections of construction activities, Tukwila will need to develop an
approach for inspections of privately -owned stormwater facilities such as detention ponds
and vaults.
Inspection and enforcement activities have drainage and water quality benefits.
4.3.1.5 Illicit Discharge Detection and Elimination
Illicit discharge detection and elimination is an NPDES Phase H permit requirement. The
permit requires the City to have an ongoing program to detect, remove, and prevent illicit
connections, discharges, and improper disposal, including spills, into the surface water
system. The permit requires full implementation of an illicit discharge and elimination
Disconnecting homes from septic systems and connecting them to piped sewers is a
structural solution aimed at reducing the risk of malfunctioning septic systems affecting
receiving water quality.
Illicit discharge detention and elimination would benefit water quality.
4.3.1.6 Public Involvement
Public involvement can promote awareness of and foster a sense of responsibility for the
health of the watersheds of Tukwila and of the greater Puget Sound, and help identify
problems and solutions. Engaging citizens in the reporting and documenting of surface
water problems through phone hotlines increases detection of problems.
Environmental stewardship activities should be increased. Individually targeted groups
should include children, students, adults, and visitors. Public involvement activities can be
coordinated with the educational activities mentioned previously. Volunteers can perform
stream buffer planting, become stream watchers, and plant trees both on their own property
and in public spaces.
Public Involvement would benefit drainage, water quality, and aquatic habitat.
4.3.1.7 Surface Water System Maintenance
Currently, Tukwila City maintenance staff perform maintenance of the surface water
system, including pipes, manholes, inlets and catch basins, ditches, open streams, and pump
stations. Because of demands on limited resources, maintenance is too often done in
response to a drainage complaint or issue rather than proactively. Proactive maintenance
may also benefit water quality and aquatic habitat by reducing total sediment load to creeks.
An example of this is cleaning out catch basins more often than required by the NPDES
Phase II permit in sensitive areas such as near salmon- bearing creeks.
Tukwila is required to ensure maintenance of private stormwater facilities in NPDES Phase
II areas according to their NPDES Phase II permit. According to the permit, the City must
er7
22
CITY OF TUKWILA 2012 SURFACE WATER COMPREHENSIVE PLAN
have a regular inspection plan for both public and private facilities. In addition to the
inspection program, the City must have a program to work with private property owners to
ensure that maintenance of the private facilities is occurring.
Maintenance benefits drainage, water quality, and aquatic habitat.
4.3.2 Capital Project Solutions
Capital projects implemented as part of a comprehensive capital improvement program can
together address many of the surface water problems identified in the City of Tukwila.
Capital projects have the potential to reduce and /or store stormwater volumes, reduce peak
flows, improve water quality, and restore aquatic habitat. This section includes descriptions
of the methods that can be utilized to address these surface water issues using capital
projects. The type(s) of surface water issues that could be addressed by capital projects are
summarized in Table 6. The remainder of this sub section discusses each of the types of
capital projects in further detail. Capital project types are organized by surface water issue
type (drainage, water quality, and aquatic habitat).
TABLE 6
Surface Water Issue Types Addressed by Capital Projects
4-8 WBG031611103411SEAl SURFACEWATERCOMPP LAN_DRAFT2012_0831 -REV
23
Surface Water Issue Type
Water Aquatic
Capital Project Type
Drainage
Quality Habitat
Increase conveyance capacity
x
Provide drainage system (or re -route
x
existing)
Infiltration
x
x
On -site detention /retention
x
x
Regional detention /retention
x
x
Velocity Reduction (check dams, etc.)
x
x
High flow bypass
x
x
Impervious surface reduction
x
x
Point source control
x
Water quality treatment
x
Conveyance system cleaning and
x
x
inspection
Land acquisition
x
x x
Riparian buffer restoration protection
x
x x
Channel stabilization
x
Channel physical habitat restoration
x
Replacement of culvert or other
x
infrastructure to be fish passable
4-8 WBG031611103411SEAl SURFACEWATERCOMPP LAN_DRAFT2012_0831 -REV
23
4.0 SURFACE WATER ISSUES AND SOLUTIONS
4.3.2.1 Drainage
Capital projects meant to address altered hydrology (that is, water quantity) include
infiltration, regional detention /retention, onsite detention /retention, reductions in
impervious surface, velocity reduction, high -flow bypass facilities, dispersion, stream buffer
restoration, and land purchase. The effectiveness of any of these alternatives can be limited
by physical space constraints. The feasibility of any of these alternatives is also often limited
by topography, soil conditions, and the presence of sensitive areas.
Increasing Conveyance Capacity of a drainage network is often performed to alleviate
localized drainage issues. Pipes are removed and replaced with a larger diameter pipe.
Hydraulic and hydrologic analysis should be performed in order to assess downstream
impacts of proposed conveyance capacity changes.
Providing a drainage network where there is currently a formal system will provide
conveyance of stormwater away from a location. Lack of a formal (that is engineered or
planned) drainage network is common in areas developed before current stormwater
standards.
Infiltration is an extremely effective method to reduce stormwater runoff volumes and peak
flows. Under pre development conditions, a significant portion of the annual precipitation
infiltrates into the ground. After development and the corresponding increase in impervious
surfaces that prevent infiltration, much more of the annual precipitation runs off as
stormwater. Promoting infiltration is a method to reduce the impacts of development by
mimicking natural hydrologic processes.
Infiltration effectiveness is a function of soil infiltration capacity. Many areas of Tukwila
have top soils conducive to infiltration. When local soils are not conducive to infiltration,
soils amended with organic material can be brought in and placed over native soils. Even if
the native underlying soils have low infiltration capacity, the infiltrated water will use the
storage available in the soil column of the amended soil layer until infiltration into the
underlying layer is possible. Moisture retained in the amended soil layer is available for
plant uptake, including lawns.
During construction activities, it is common for the native top layer of soil to be stripped
away. In this case, amended soils should be introduced rather than relying on the remaining
native soils. Planting, then maintaining, a lawn on the remaining native soil will require
watering and fertilizing that would not be necessary if the native top layer were still in place
or if amended soils were brought in.
Regional detention/retention is a plausible structural solution. Regional detention could be
used to detain erosive peak flows. Total volumes of stormwater runoff can be reduced
through retention via evaporation, plant uptake, and infiltration. In addition to
implementation of new facilities, existing regional detention facilities can be retrofitted to
promote capacity and capability.
Onsite detention/retention and other site specific measures are also effective at detaining
peak flows and decreasing total volumes of stormwater runoff. Onsite detention and other
site specific measures on public, City -owned property are considered capital project and are
therefore discussed in this section. Onsite detention and other site specific measures on
IT?TtTlkf3iilkii�']1•I T* tTi13��tTrT�7e1 ".'�R1�1I771�ik,I lTk
24
CITY OF TUKWILA 2012 SURFACE WATER COMPREHENSIVE PLAN
private property are discussed in the programmatic solutions section under education,
incentives, and regulations. That said, it may be feasible to use public funds to fund on -site
detention on private property if the benefit is shared by a larger group than just the private
property owner. Dispersion, for purposes of this discussion, is considered a type of on -site
stormwater management
Reductions in impervious surface can reduce runoff volumes and velocities. Low Impact
Development (LID) regulations can promote reduced widths of newly constructed
roadways and is covered in the regulations section (programmatic), but retrofitting existing
infrastructure is a structural solution. Pilot projects for reducing road widths and using
permeable pavements can be implemented within the City to address water quantity
concerns.
Conveyance system cleaning and inspection provides information as to the condition of
the stormwater conveyance system that allows for prioritization of rehabilitation, repair, or
replacement efforts. In addition, cleaning of the conveyance system can increase the
effective conveyance capacity by removing accumulated sediment and other material. Water
quality benefits may also be obtained by removing that sediment from the stormwater
system.
Stormwater runoff velocities can be reduced using check dams and vegetation in existing
ditches. In addition, high -flow bypass facilities can be installed in areas that are prone to
erosion under high flow regimes. Stream buffer restoration can reduce stormwater
volumes via plant uptake and reduce stormwater velocities by adding roughness to the flow
path. Land acquisition can be an effective method to reduce developed land surface and
therefore reduce impervious surface, promote infiltration, and retain the natural tree
canopy.
4.3.2.2 Water Quality
The most effective methods to reduce pollutant loading to the City of Tukwila's receiving
waters are controlling pollutants at the source and controlling stormwater flows (that is,
peak flows and volumes). Water quality treatment can also be an effective method but
effectiveness is often limited by available technology. Channel stabilization also has water
quality benefits.
Source control measures tend to be programmatic in nature rather than structural and are
therefore addressed in the programmatic solution section. However, control of point source
water quality problems is covered in this section.
Alternatives geared towards reducing volumes and peaks of stormwater runoff discussed in
the drainage section also have positive impacts on pollutant inputs by reducing erosion and
erosive capabilities of stormwater and by reducing total stormwater inputs to receiving
water bodies. These solutions include infiltration, regional or on -site detention or retention,
impervious surface reduction, velocity reduction, stream buffer restoration, and land
purchase.
The effectiveness of water quality treatment as an alternative is limited by available
technology. Total suspended solids (TSS) is relatively easy to remove but other pollutants
such as nutrients and heavy metals are not. Particulate -bound copper can be removed via
4-10
25
4.0 SURFACE WATER ISSUES AND SOLUTIONS
treatment, but dissolved copper is difficult to remove. Though particulate -bound copper can
be removed using sedimentation and filtration, dissolved copper requires adsorption,
precipitation, or separation.
The pollutant removal capabilities of stormwater treatment is dependent upon the
concentrations of pollutants entering the treatment facility. The lower the influent
concentration, the harder it is to remove. The term "irreducible limits" refers to the
concentration at which no more of a constituent can be removed. The irreducible limit
depends on available technology. The higher the influent concentration, the easier the
constituent is to remove.
Channel stabilization can be used to reduce channel erosion propagated by increasing
stormwater peak flows and volumes. This structural solution can prevent significant erosion
and minimiz the risk of increasing channel incision (that is, down cutting).
The selection of a preferred water quality solution is dependent upon pollutants of concern
in the receiving water body.
4.3.2.3 Aquatic Habitat
Structural solutions aimed at aquatic habitat restoration include replacing culverts, flap
gates, or other structures that block fish passage, restoration of physical features of creek
and river channels, and riparian buffer restoration and protection. Any of these solutions
can aid in aquatic habitat restoration. This Plan contains an inventory of blockages to fish
passage in the Gilliam, Riverton, Southgate, and Johnson Creeks. Restoring physical
features of creek channels and protecting and restoring stream buffers also have water
quantity and water quality benefits, in addition to aquatic habitat benefits. Note that habitat
restoration or protection projects on the Green or Duwamish Rivers will require significant
partnerships with regulatory agencies and with other municipalities such as King County.
Land acquisition can be an effective method to reduce developed land surface and therefore
promote infiltration, retain the natural tree canopy, and restore stream buffers. Retention of
the natural tree canopy and restoration of stream buffers promote improvement of aquatic
habitat.
4.4 Solutions to Tukwila's Surface Water Issues
The purpose of this sub section is to specify individual solutions to the surface water issues
outlined earlier in this section. Table 7 outlines all major surface water issues identified
during this planning effort. All of the surface water issues identified have been assigned one
or more possible solutions. Each issue can be wholly or partially addressed by that, or those,
solutions. Note that City -wide problems will need to be addressed by either a programmatic
activity (such as a regulatory change) or else as a series (or program) of capital projects.
Problems identified at specific locations may be addressed by a capital project, a
programmatic action, or a combination of both programmatic and capital investment.
A recommended solution is also shown in Table 7.
In addition to the specific surface water issues shown in Table 7, several smaller drainage
issues have been identified by the City of Tukwila and have been included on the Small
4419
26
CITY OF TUKWILA 2012 SURFACE WATER COMPREHENSIVE PLAN
Drainage Project List. The drainage issues on the Small Drainage Project List are addressed
as a small drainage program.
Note that both the programmatic activities and capital projects recommended as part of this
Plan are described in Section 7 (Recommendations). Section 5 provides specific details of the
operations and maintenance programmatic activities and Section 6 provides a listing of the
capital projects.
4-12
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5.0 Capital Improvement Projects
This section summarizes the eighteen capital improvement projects recommended for
inclusion into the City of Tukwila's capital improvement program. These capital projects are
organized by fund (412 Fund for drainage and water quality shown in Table 8 and 301 Fund
for fish habitat shown in Table 9). Figure 7 shows the locations of each of these capital
projects. Appendix E contains the details for each capital project, including cost estimates.
5.1 412 Fund (Drainage and Water Quality)
TABLE 8
Drainage and Water Quality Capital Projects 412 Fund
Estimated Total Project
6'S
32
Cost (March 2012
ID
Project Name
Basin
Dollars)
98641222
S 143 St storm drain system
Duwamish River
$1,096,000
98741202
Nelson /Longacres Phase II
Nelson /Longacres
$678,000
98941202
Christensen Rd. pipe
Gilliam Creek
$327,000
replacement
99341208
Gilliam Creek 42 Ave S culvert
Gilliam Creek
$702,000
99441202
Soil Reclamation Facility
Nelson /Longacres
$3,504,000
90341206
Northwest Gilliam Storm
Gilliam Creek
$1,978,000
Drainage System
90341213
53` Ave S storm drain system
Duwamish River
$1,557,000
90341214
S146 th St pipe and 25` Ave S
Southgate Creek
$882,000
drainage
91041203
Storm Lift Station No. 15
P17
$698,000
Improvements
91041204
E. Marginal Way S Stormwater
Duwamish River
$772,000
Outfall
91241201
Water Quality Retrofit Program
Duwamish River
$287,000
91241202
Tukwila Pkwy /Gilliam Cr Outfalls
Gilliam Creek
$278,000
91241203
Tukwila Urban Center
Gilliam Cr. /P17
$541,000
Conveyance Inspections
91041204
E. Marginal Way Conveyance
Riverton Creek
$85,000
Inspection
6'S
32
0
6
33
D4120
180th
t
P uJget Sound I
JohnSer 20 th
V
Capital Improvement Projects
City of Tukwila
Stormwater Pipe
Drainage
King County Unincorporated
Drainage Basins
A Drainage/Habitat
Other Municipalities
A Outfall
0 Habitat
33
5.0 CAPITAL IMPROVEMENT PROJECTS
5.2 301 Fund (Fish Habitat)
TABLE 9
Fish Habitat Capital Projects 301 Fund
Estimated Total Project
5-3
34
Cost (March 2012
ID
Project Name
Basin
Dollars)
90330104
Nelson Side Channel
Nelson /Longacres
$1,497,000
90630102
Duwamish Gardens
Duwamish
$3,000,000
99830103
Riverton Creek Flap Gate
Riverton Creek
$946,000
Removal
99830105
Gilliam Creek Fish Barrier
Gilliam Creek
$816,000
Removal
5-3
34