HomeMy WebLinkAboutPlanning 2019-02-28 Item 4 - Attachments - Critical Areas ReportJ. S. Jones and Associates, Inc.
Type 4 Watercourse Buffer Enhancement Plan
and Justification for Buffer Reduction
of the
15404 40th Avenue South Property
King County Tax ID No.: 004300-0266
Prepared for:
FLS Development, LLC
155 SW 152nd Street, #A
Seattle, Washington 98166
206-423-8425
Dated:
May 14, 2010
Prepared by:
Lance Erickson, Environmental Designer
rimer 0
AUG 12 20 I
o p vuo,
402 EAST MAIN STREET, SUITE 110
AUBURN, WASH 1 N G T O N 9 8 0 0 2
253-804-2645 / FAX 253-333-8584
17
Executive Summary
The subject property is located at 15404 40th Avenue South, in Tukwila, Washington. A Type 4
watercourse is located between the north property line and South 154th Street. Type 4 watercourses are
required to have a 50-foot buffer in the City of Tukwila. The applicant proposes to reduce the buffer
by 50% and enhance the remaining buffer area. No evidence of additional sensitive areas are present
south of the Type 4 watercourse. The remainder of the property is dominated by invasive vegetation
which include Himalayan blackberry and non-native grasses. The applicant proposes to remove the
invasive vegetation within the proposed enhancement area and install native trees and shrubs. The
total area of enhancement is 3,057 square feet. The enhancement area will be planted with plant
materials native to the Puget Sound lowlands. Native plant species will increase plant diversity,
wildlife habitat and prevent the establishment of invasive species. In addition to the proposed
enhancement, the reduced buffer will be fenced with split rail fencing and stream buffer signs will be
posted. Detailed plans documenting the proposed enhancement are shown on the attached mitigation
plan.
Figure 1.0
Proposed buffer
reduction and
enhancement area
(existing lawn located in
the northwest corner of
the subject property)
Baseline Information
The subject property is located at 15404 40th Avenue South, in Tukwila, Washington. The tax parcel
number is 00430-0266. The property is located in the southwest quarter of Section 22, Township 23,
Range 04 East of the Willamette Meridian.
A watercourse flows from a culvert under 40th Avenue South and runs parallel to the north property
line. The watercourse is located in the vacated Right of Way for South 154th Street. The stream is
rated as a Type 4 Watercourse. Section 18.45.100.A.4 of the Tukwila Municipal Code (TMC) defines
Type 4 Watercourses as "those watercourses that have intermittent flows and are not used by salmonid
fish." Type 4 Watercourses are required to have a 50-foot wide buffer. No evidence of additional
sensitive areas are present south of the Type 4 watercourse. The remainder of the property is
dominated invasive vegetation which include Himalayan blackberry and non-native grasses. Most of
the eastern portion of the property is being used as residential lawn. The property slopes
approximately 5% to the east. A residence and four associated out buildings (a detached garage and
three sheds) are present. Multi -family residences are present to the south and east.
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J. S. Jones and Associates, Inc.
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Figure 2.0
Type 4 Watercourse
(view from side walk at
northeast corner of
property)
The TMC allows for buffer width variations. Section 18.45.10.F.1 of the TMC states "The Director
may reduce the standard watercourse buffers on a case -by -case basis, provided the buffer does not
contain slopes 15% or greater. The approved buffer width shall not result in greater than a 50%
reduction in width. Any buffer reduction proposal must demonstrate to the satisfaction of the Director
that it will not result in direct, indirect or long-term adverse impacts to watercourses." The applicable
sections of the TMC are attached.
Justification for Buffer Reduction
This action is permitted in the TMC in Section 18.45.100.F.la which states: "The Director may reduce
the standard watercourse buffer on a case -by -case basis, provided the buffer does not contain slopes
15% or greater. The approved buffer width shall not result in greater than a 50% reduction in width.
Any buffer reduction proposal must demonstrate to the satisfaction of the Director that it will not result
in direct, indirect or long-term adverse impacts to watercourses, and that b), if there is no significant
vegetation in the buffer, a buffer may be reduced only if an enhancement plan is provided. The plan
must include using a variety of native vegetation that improves the functional attributes of the buffer
and provides additional protection for the watercourses functions and values."
The proposed buffer reduction meets the required conditions as follows:
• The buffer is Tess than 15% slope
• The proposed reduction is not greater than 50%
• The existing buffer is mowed and maintained lawn, invasive Himalayan blackberry, and un-
maintained grasses. In is current state the buffer provides little to no function or values to the
Type 4 Watercourse. Enhancement will increase the functions and values of the buffer.
• Enhancement with native trees and shrubs will increase both the function and the value of the
buffer area. Native trees and shrubs will increase will increase plant diversity, wildlife habitat
and prevent the establishment of invasive species.
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Environmental Goals and Objectives
The goal of mitigation is to increase the functions and values of the existing Type 4 Watercourse
buffer through enhancement. The area of stream buffer which is proposed to be reduced is currently
maintained lawn, invasive Himalayan blackberry, un-maintained grasses and weeds. Enhancement
will provide a greater functions and values by improving plant diversity, wildlife habitat, and
protection for the off -site watercourse. The objectives necessary to meet the above stated goal area as
follows:
• Remove invasive vegetation from the stream buffer
• Remove trash and debris from the stream buffer
• Install native vegetation within the stream buffer
• Install split rail fencing and stream buffer signs at the limits of the proposed buffer deter future
intrusions into the sensitive area
• Maintain and monitor the enhancement area for a period of three years or until the site meets
the specified performance standards
• Record the sensitive area in a "Notice on Title"
• If the enhancement area fails to meet performance standards provide a contingency plan to
rectify the situation.
Buffer Reduction and Mitigation
The area of the existing 50-foot buffer is 8,009 square feet. The applicant proposes a 50% reduction
for enhancement. The remaining buffer area to be enhanced is 3,057 square feet. Section
18.45.10.F.1.B of the TMC, allows for reduction of a watercourse buffer by up to 50% if there is no
significant vegetation present and an enhancement plan is provided. The western portion of the on -site
buffer area is dominated by mowed and maintained lawn. The eastern portion is dominated by
invasive Himalayan blackberry and un-maintained grass and weeds (see Figure 1.0 and Figure 3.0).
The applicant proposes to remove the weeds and invasive vegetation and replant the area with native
trees and shrubs. Native plant species will increase plant diversity, wildlife habitat and prevent the
further establishment of invasive species. One existing maple tree will remain in the buffer area. No
impacts to the Type 4 watercourse are proposed.
Plant quantities were calculated on a 9'x 9' spacing for trees and 5'x 5'spacing for shrubs. 40 trees
and 120 shrubs are proposed for installation within the enhancement area. The enhanced buffer will be
fenced with split rail fencing. Two stream buffer signs will be posted on the split rail fence. Details
for split rail fencing and stream buffer signs are shown on the attached planting plans.
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J. S. Jones and Associates, Inc.
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Figure 3.0
Invasive plant material and
existing landscape trees in
the mitigation area.
Performance Standards
The plant survival and cover standards established to measure the success of the mitigation area are as
follows:
Year 1
Year 2 Year 3
Shrub and Sapling Tree Cover* >10% >15% >20%
Shrub and Sapling Tree Survival 100% >85% >80%
*Includes beneficial native plants in that category that are naturally recruiting volunteers
• Less than 10% invasive vegetation during any monitoring event.
• The establishment of 3 species of native trees and 4 species of native shrubs at the end the
monitoring period.
Monitoring Program
The applicant's environmental consultant will perform a three-year monitoring program. A monitoring
report will be submitted to the City of Tukwila by December 31 st of each year beginning the first fall
after enhancement installation. Sample points or transects will be established for vegetation
monitoring. Photo -points will be established from which photos will be taken throughout the
monitoring period. Linear transects are the preferred method for vegetation monitoring for this site.
No less than one (1) 50 foot transect will be established in the mitigation area. Permanent transect
location(s) must be identified on the approved mitigation plans in the first monitoring report (they may
be drawn on approved mitigation plans by hand). Plots located at the end of each transect shall detail
herb, shrub, and tree aerial cover at radii of 1m, 5m, and 10m respectively, using the Braun-Blanquet
releve method or other acceptable field method. Monitoring of vegetation transects shall occur
annually between August 1 and September 30, prior to leaf drop, unless otherwise specified.
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J S. Jones and Associates. Inc.
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As applicable, the monitoring reports must include description/data for:
• Project reference number
• Site plan and location map
• Historic description of the project, including date of installation, current year of monitoring,
restatement of enhancement goals, and performance standards
• Plant survival, vigor, and aerial coverage from every plant community and an explanation of
monitoring methodology in the context of assessing performance standards
• Hydrologic data from wells, hand -ball test, and visual observations, and an explanation of
monitoring methodology
• Buffer conditions, e.g. surrounding land use, use by humans, wild and domestic creatures
• Observed wildlife, including amphibians, avians and others
• Assessment of nuisance/exotic biota and recommendations for management
• Receipts for off -site disposal of any dumping, weeds or invasive plants
• Receipts for structural repairs or replacement
• Color photographs taken from permanent photo -points as shown on enhancement plan
• Summary of maintenance and contingency measures proposed for next season and completed
last season
Maintenance Plan
In order to achieve performance standards, the applicant shall have the mitigation area maintained for
the duration of the monitoring period. Maintenance shall be required in accordance with City of
Tukwila guidelines and approved plans. Maintenance activities will be conducted a minimum of twice
per year (April and September) for the duration of the monitoring period, three years. Maintenance
will include:
• Watering
• Weeding around base of installed plants
• pruning
• Replacement
• Restaking
• Removal of all classes of noxious weeds (see Washington State Noxious Weeds List, WAC 16-
7150-005) as well as Himalayan blackberry
• Any other measures needed to insure plant survival
• General maintenance activities which include the replacement of any vandalized or damaged
signs, habitat features, fences or other structural component of the mitigation site.
Chemical controls shall not be used in the mitigation area. However, limited use of herbicides may be
approved depending on site specific conditions, only if approved by City of Tukwila staff. All
invasive material and debris is to be disposed of off -site in a legal manner. The Permittee shall be
responsible for the health of 100% of all newly installed plants for one growing season after
installation has been accepted by City of Tukwila staff. A growing season for these purposes is
defined as occurring from spring to spring (March 15 to March 15, following year). The Permittee
shall replace any plants that are failing, weak, defective in a manner of growth, or dead during this
growing season, as directed by the Landscape Designer, Wetland Biologist, and/or City of Tukwila
staff. Water shall be provided during the dry season (July 1-October 15) for the first two years after
installation to ensure plant survival and establishment. Water should be provided by a temporary
above ground irrigation system. Water should be applied at a rate of 1" of water two times a week for
Year 1 and 1" of water one time a week during Year 2.
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J S. Jones and Associates, Inc.
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Contingency Plan
Should any monitoring report reveal the enhancement has failed in whole or in part, and should that
failure be beyond the scope of routine maintenance, a contingency plan will be submitted. Once
approved, it may be installed, and will replace the approved enhancement plan. If failure is substantial,
the City of Tukwila may extend the monitoring period for the enhancement.
Performance Bonds
Prior to beginning any work, the Permittee must provide a mitigation bond or assignment of funds per
City of Tukwila procedures. A bond quantity worksheet has been completed based on all elements of
the mitigation plan. The total cost, plus contingency fees has been determined to be $ 13,894.37 ,
which will be the amount of the mitigation bond the Permittee is required to provide.
Critical Areas Mitigation
Bond Quantity Worksheet
Project Name: Tukwila Property Date: 5/14/10 Prepared by: J. S. Jones and Associates, Inc.
Location: 15404 40th Avenue South Applicant: FLS Development, LLC Phone: 206.423.8425
PLANT MATERIALS'
Type Unit Price I Uni Quantity
Descrt on
Cost
PLANTS: Container, 1 gallon, medium sod I 311.50 Each 105
a .,.
$ 1.207.50
PLANTS: Container, 29allen, medium soil I 320.00 Each 15
5 300.00
$ 1,440.00
PLANTS Container, 5 gallon, medium sod I 336.001 Each, 40
• All cods include nwaadm ....'TOTAL
$ 2,947.50
INSTALLATION COSTS ( LABOR, EQUIPMENT, 8. OVERHEAD)
Type Und Price I Unit
... ...............
general ) 540.001 2I
960.00
Hauling and disposal : 54001 Cyr 4
Mulch, delivered and spread 335.7 CY 5
S 960.00
5.... 178.65
__.. .....
TOTAL
S 1,338.65,
GENERAL ITEMS
ITEMS Unit Cost
Uni
Cost
II Fencnsokt rail. 3' hi (2.aat( ..... 310.54
L
185
,.,.
S 1.949.90
Signs sensitive area boundary (in backing, post in I) 328.5
Each
2
TOTAL
$ ...... 57.00
S 2,008.90
OTHER
'', (Construction Cost SubtotelJ
S 8,293.05
ITEMS
rercentagee1
nstruction
Unit
Cost
Modgzabon 10%�.�.$
629.31
.._ ...... I .. 30%
Contingency
(TOTAL
$ 1,887.92
5.... 2,517.22 I..
NOTE Projects with multiple permit requirements may be required to have longer
MAINTENANCE AND MONITORING monitoring and maintenance terms. This will be evaluated on a case -by -case
basis for development applications. Monitoring and maintance ranges may 61
'I. assessed anywhere from
Maintenance, Twice/Annual
n.,.,..,..�.._..._...
I.
Larger than 1,000 sq. fL but less than 5.000 sq.8. cr button
mitigation
$ 180.00
EACH
9I4hr t $45lhr)
S 1,620.00
Mongering, annual
Larger than 1,000 sq.ft but less Than 5,000 -butter mitigation
on ....
S 720.00
EACH' 3I(8 hrs q51 90/hrl
S 2,180.00
Maintenance and Monitoring Inspection (City), annual
3382.25
EACH( 2 (2.5 hrs r. $144.90/hr)
S 724.50
Maintmance and Monitoring Inspec5m (City), final
3579.80
EACHI 1 (4 hrs $144.90/hr)
S 579.60
r _.. 'TOTAL
', $ 5,084.10 '..
Total $13,894.37
May 20/0
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J. S. Jones and Associates. Inc.
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REVISED FINAL WETLAND MITIGATION PLAN
TUKWILA POND
Tukwila, Washington
Prepared for
Wig Properties LLC-SS
4811 SE 134th Place SE
Bellevue, Washington 98006
Prepared by:
Chad Armour LLC
6500 126th Avenue SE
Bellevue, Washington 98006
(425) 641-9743
August 2006
RECENED
AUG 14 2006
1 o ihf u;,i t'f
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Revised Final Wetland Mitigation Plan Wig Properties LLC-SS
Tukwila, Washington
TABLE OF CONTENTS
1. EXECUTIVE SUMMARY 1
2. PROJECT DESCRIPTION 3
2.1 PROJECT LOCATION 3
2.2 RESPONSIBLE PARTIES 3
2.3 DESCRIPTION OF THE OVERALL PROJECT 3
3. BASELINE INFORMATION 4
3.1 WETLANDS ON THE PENNEY SITE 4
3.1.1 Wetland A 4
3.1.2 Wetland B 4
3.1.3 Wetland C 4
3.1.4 Wetland D 4
3.1.5 Wetland E 5
3.1.6 Wetland F 5
3.1.7 Wetland Ratings 5
3.1.8 Wetland Functions 5
3.1.9 Fauna Associated with the Penney Wetlands 5
3.2 TUKWILA POND SITE 5
3.2.1 Existing Vegetation 6
3.2.2 Existing Soils 6
3.2.3 Existing Hydrology 6
3.2.4 Wetland Ratings 7
3.2.5 Wetland Functions 7
3.2.6 Tukwila Pond Fauna 7
3.3 PRECIPITATION ANALYSIS 7
4. PROBABLE IMPACTS OF THE PROPOSED DEVELOPEMENT 8
4.1 SHORELINE PROTECTION 8
4.2 HYDROLOGIC SUPPORT 8
4.3 STORM/FLOOD WATER ABATEMENT 9
4.4 GROUNDWATER EXCHANGE 9
4.5 WATER QUALITY IMPROVEMENT 10
4.6 BIOLOGICAL SUPPORT 10
5. MITIGATION APPROACH 11
5.1 CODE COMPLIANCE 11
5.1.1 Permitted Alterations 11
5.1.2 Mitigation Sequencing 12
5.1.3 Mitigation Plans 12
5.1.4 Mitigation Location 13
5.2 RATIONALE FOR CHOICE 13
5.2.1 Case Study 13
5.2.2 Projected Conditions of the Mitigation Site 14
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Revised Final Wetland Mitigation Plan Wig Properties LLC-SS
Tukwila, Washington
5.3 CONSTRAINTS 14
5.4 GOALS AND OBJECTIVES OF THE MITIGATION PLAN 14
5.4.1 Goals 14
5.4.2 Objectives 14
5.5 PERFORMANCE STANDARDS 15
5.5.1 Hydrology 15
5.5.2 Soil 16
5.5.3 Vegetation 16
5.5.4 Structure 17
6. CONSTRUCTION PLAN 17
6.1 HYDROLOGY 18
6.2 SOILS 18
6.3 VEGETATION 18
6.4 HABITAT STRUCTURES 19
6.5 INSTALLATION SEQUENCE 19
7. MONITORING PLAN 20
7.1 PRE -CONSTRUCTION MONITORING 20
7.2 CONSTRUCTION MONITORING 20
7.3 POST -CONSTRUCTION MONITORING 20
7.3.1 Hydrology 21
7.3.2 Soils 21
7.3.3 Vegetation 21
7.3.4 Fauna 21
7.3.5 Habitat Structures 21
7.3.6 Water Quality 21
7.3.7 Buffers 21
8. SITE PROTECTION 22
9. MAINTENANCE PLAN 22
10. CONTINGENCY PLAN 22
10.1 POST A BOND 23
10.2 INSTALL PLANTS SUITED TO SEASONAL FLOODING 23
10.3 ANNUAL MONITORING FOR THE FIRST 5 YEARS 23
10.4 REMOVE ALL REED CANARYGRASS 23
10.5 INSTALL ADDITIONAL PLANTS AS NECESSARY 23
11. SCHEDULE 24
12. PERFORMANCE BOND 24
13. LIMITATIONS 24
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Revised Final Wetland Mitigation Plan
Tukwila, Washington
Wig Properties LLC-SS
Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
REFERENCES
TABLES
Wetland Functional Assessment of Various Wetlands
Pre- and Post -Construction Water Detention and Water Quality Comparison
Groundwater and Surface Water Elevations in the Tukwila Pond Mitigation Area
Comparative Analyses of Precipitation Records
Functional Wildlife Habitat of Various Wetlands
Plants to be Installed on the Mitigation Site
FIGURES
Vicinity Map
Wetlands on the Penney Site
Upland Location Plan
Comparative Precipitation Analyses
Grading Plan
Planting Plan
APPENDIX A
U.S. Army Corps of Engineer Jurisdictional Determination of Wetlands on the Penney site
U.S. Army Corps of Engineer Recommendation for Off -Site Mitigation
Washington Department of Ecology Recommendation for Off -Site Mitigation
U.S. Army Corps of Engineer Nationwide Permit 39 Notification
APPENDIX B
Wetland Rating for the Penney site
Wetland Rating for the Tukwila Pond site
Wetland Rating for the Mitigation site — Existing Conditions
Wetland Rating for the Mitigation site — Projected Conditions
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Revised Final Wetland Mitigation Plan Wig Properties LLC-SS
Tukwila, Washington
1. EXECUTIVE SUMMARY
Wig Properties LLC-SS (Wig) plans to construct the Southcenter Shopping center on the 18.77-
acre Penney warehouse distribution site in Tukwila, Washington (Figure 1). To do so, Wig
proposes to fill 1.16 acres of wetlands that developed on fill soil placed on the Penney site in the
late 1960s (Figure 2).
Based on the City of Tukwila's (Tukwila) wetland rules, four of the six Penney site wetlands
meet the criteria for Type 3 wetlands. The other two are unregulated. The U. S. Army Corps of
Engineers (Corp) determined that only one of the six wetlands on the Penney site is
jurisdictional and therefore regulated by the Corps (Appendix A). All six of the Penney site
wetlands are regulated by the Washington Department of Ecology (Ecology).
As a whole the wetlands on the Penney site exhibit low wetland functions because they are
small and support immature plant communities that developed on imported fill soils (Table 1).
Upon closer inspection, the Penney site wetlands exhibit high water quality functions and low
hydrologic and habitat functions. The road ruts that support wetlands store water that would
otherwise be released quickly to the tower Green River. They also provide limited water quality
improvement and biological support.
To mitigate for filling the Penney site wetlands, Wig proposes to create and enhance a total of
3.48 acres of lacustrine emergent and open water wetland dominated by reed canarygrass
(Phalaris arundinacea). The mitigation site is located in the southeast quadrant of the 24-acre
Tukwila Pond site. It is surrounded by open water, scrub -shrub and forested wetland, forested
upland, and upland shrubs.
The Tukwila Pond site as a whole, rates at the low end of Category II wetlands (Appendix B).
Its water quality functions rate high and it's hydrologic and habitat functions are rated as
moderate. The mitigation site currently rates as a solid Category III wetland. It has a moderate
rating for water quality and hydrologic functions and a low habitat function. Following
completion of mitigation and at the end of the 10-year monitoring and maintenance effort, the
Mitigation site is projected to function as a high end Category II wetland. The Tukwila Pond site
is located about 1,000 feet northeast of the Penney site.
The Tukwila Pond was selected for mitigation for the following reasons:
• The quality of the existing wetland at the Tukwila Pond site can be substantially
improved (Tablet);
• Both Ecology and the Corps prefer that mitigation occur off site (Appendix A);
• The sensitive areas regulations allow for off site mitigation;
• Tukwila's long-term plans include enhancing degraded portions of the Tukwila Pond
site;
• The mitigation site is located in the same drainage basin as the Penney site; and
• The mitigation site is bounded by existing open water and forested wetlands as well
as upland forest and shrub plant communities.
In addition to providing compensation for wetland loss, the benefits of the wetland mitigation
plan include:
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Revised Final Wetland Mitigation Plan Wig Properties LLC-SS
Tukwila, Washington
• Increasing the complexity of the Tukwila Pond site; and
• Increasing the detention capacity of the Tukwila Pond.
In addition to providing these benefits, the wetland mitigation plan is designed to more than
replace the wetland functions that will be lost on the Penney site. Filling the Penney site
wetlands will have minimal impact on the hydrological support function because their
contribution to base flow is very small. Conversely it will have a positive effect on floodwater
abatement and water quality improvement. The shopping center's stormwater management
system together with the new detention capacity on the Mitigation site represents a 574 percent
increase over existing conditions (Table 2). Similarly, the shopping center's water quality
system and landscaping together represents a 1,345 percent increase in water quality treatment
capacity. Replacing the immature forest and meadow habitat present on the Penney site with
four wetland classes, including open water, will more than offset the lost habitat functions (Table
1).
Wig recognizes that it is likely that some of the plants installed on the Mitigation site will not
survive the seasonal flooding typical of the Tukwila pond. Wig also recognizes that seasonal
flooding tends to favor reed canarygrass. To reduce these potentials Wig will:
• Install plants that tolerate seasonal flooding;
• Monitor the Mitigation site for 10 years — annually for the first 5 years;
• Install new plants annually to replace those that are lost; and
• Post a bond sufficient to cover the cost of replanting the Mitigation site.
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Revised Final Wetland Mitigation Plan Wig Properties LLC-SS
Tukwila, Washington
2. PROJECT DESCRIPTION
This plan presents information about the proposed Southcenter Square Shopping Center project
(Proposed Development), the wetlands that are present on the Penney site, the land present in
the southeast quadrant of the Tukwila Pond site, and the mitigation plan designed to
compensate for lost wetland functions due to the Proposed Development.
2.1 Project Location
The Proposed Development is located in Tukwila, Washington (King County) in Sections 26,
Township 23 North, Range 4 East (Willamette Meridian) (Figure 1). It is bounded by
Southcenter Parkway to the west, Minkler Boulevard to the south, the Bon distribution
warehouse to the north, and a business park to the east. The Mitigation site is located within a
larger parcel typically referred to as the Tukwila Pond. The Mitigation site is located west of
Andover Parkway West (Andover).
2.2 Responsible Parties
The following key people are responsible for this project:
Ms. Leshya Wig, Project Manager
Wig Properties LLC-SS
4811 134th Place SE
Bellevue, Washington 98006
(425) 957-4774
Ms. Moira Bradshaw, Sr. Planner
City of Tukwila Department of Community Development
6300 Southcenter Boulevard
Tukwila, Washington 98188-2544
(206) 431-3651
Mr. Chad Armour, Principal
Chad Armour LLC
6500 126th Avenue SE
Bellevue, Washington 98006
(425) 641-6743
Mr. Armour prepared this wetland mitigation plan and delineated the wetlands on the Penney
site and the central uplands on the Mitigation site (Figure 3).
2.3 Description of the Overall Project
Wig plans to construct a commercial shopping center on the 18.77-acre Penney site. There are
currently two buildings on the western 13.55 acres of the Penney site. The eastern 5.22 acres
is the location of immature deciduous forest and meadow plant communities that developed on
fill soils. These soils were placed on the site some 35 years ago (Armour, 2004). To build the
shopping center, Wig proposes to fill 1.16 acres of low quality emergent and forested wetlands.
To mitigate for filling these wetlands, Wig proposes to enhance and/or create 3.48 acres of
existing upland and wetland present on the Tukwila Pond site. This includes creating wetland at
a ratio of 1.5:1, enhancing degraded wetland at a ratio of 3:1, and enhancing degraded wetland
at a ratio of 1:1. At the end of the 10-year monitoring the functional value of the created and
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enhanced wetlands on the Mitigation site will be considerably greater than the functions of the
existing wetlands on both the Penney and Tukwila Pond sites (Tables 1 and 2).
3. BASELINE INFORMATION
Chad Armour LLC (Armour) delineated the wetlands on the Penney site in April 2004. Armour
installed and measured the water levels in 14 shallow groundwater monitoring wells on the
Mitigation site from October 2004 to the present.
Bush, Roed & Hitchings, Inc. (BRH) is Wig's civil engineering consultant. BRH surveyed the
delineated wetland boundaries on the Penney site, calculated pre- and post -development
stormwater runoff on the same, and prepared the grading plan for the Mitigation site.
3.1 Wetlands on the Penney Site
There are six wetlands located on the Penney site (Figure 2).
3.1.1 Wetland A
Wetland A is an isolated Type 3 wetland that covers 13,718 square feet (0.32 acre). Its most
notable feature is a rutted road. Grasses and herbs dominate most of Wetland A, including the
road. Trees dominate a small portion of this wetland. The forested portion of Wetland A
occupies 2,698 square feet; almost 20 percent of the wetland. During the rainy season standing
water about 6 inches deep is present on about 75 percent of the wetland.
3.1.2 Wetland B
Wetland B is an isolated Type 3 wetland that covers 24,461 square feet (0.57 acre). Trees
dominate the western half of Wetland B. Emergent herbs typically growing in a deeply rutted
road dominate the remaining wetland. During the rainy season standing water averages about
6 inches deep; however, can be up to 1.5 feet deep in places.
3.1.3 Wetland C
Wetland C is an isolated Type 3 wetland that covers a total of 6,305 square feet (0.15 acre). It
includes a forested area that covers 40 percent of the wetland and a rutted road. The road
contains standing water during the rainy season and supports emergent vegetation. The
understory of the forested area is generally devoid of vegetation, presumably as a result of
standing water. During the rainy season 100 percent of this wetland is covered with about 6
inches of standing water.
3.1.4 Wetland D
Wetland D is a Type 3 wetland that covers 3,943 square feet (0.09 acre). Himalayan blackberry
(Rubus discolor) shrubs, grasses, and herbs dominate it. Surface water accumulates in this
wetland during the rainy season. This water discharges west to the asphalt apron and
associated stormwater drain located on the developed portion of the distribution center. After
the water enters the catch basin, it flows into a series of pipes (sizes range from about 6 inches
to 66 inches in diameter) and swales before being discharged into a King County regional
stormwater detention pond. This water is then pumped into the Green River (Clark, 2004).
Wetland D is the only wetland considered jurisdictional by the Corps (Appendix A).
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3.1.5 Wetland E
Wetland E covers 179 square feet (<0.01 acre) and is dominated by soft rush (Juncus effusus).
The slight grade of this wetland precludes standing water during the rainy season. This isolated
wetland is too small to be regulated by Tukwila, but is regulated by Ecology.
3.1.6 Wetland F
Wetland F is an isolated wetland that covers 1,971 square feet (0.05 acre). Trees dominate the
central 40 percent of this wetland. The remainder of Wetland F is dominated by emergent plant
species. Like all of the other Penney site wetlands, a rutted road represents a significant portion
of this wetland. During the rainy season standing water about 6 inches deep is present on
about 50 percent of the wetland. As with Wetland E, this isolated wetland is too small to be
regulated by Tukwila, but is regulated by Ecology.
3.1.7 Wetland Ratings
Based on Tukwila's criteria (Tukwila, 2005), the wetlands individually and collectively are rated
as Type 3 wetlands. The wetlands are classified as a Category III wetland using Ecology's
wetland rating system (Appendix B).
3.1.8 Wetland Functions
Based on the revised Washington State Wetland Rating System for Western Washington
(Hruby, 2004), the Penney site wetlands are rated at the low end of Category III wetlands (Table
1). As a whole the wetlands on the Penney site exhibit low functions because they are small
and support immature plant communities that developed on imported fill soils. When the
wetland functions are partitioned, the Penney site wetlands exhibit moderate water quality and
habitat functions and low hydrologic functions. They rated high for water quality because very
little surface water flows off of the site and the wetlands are surrounded by urban development.
The road ruts on the site that are wetlands store water that would otherwise be released quickly
to the lower Green River. We assume that this stored water infiltrates into the soil and
contributes to the regional groundwater system. These open water areas also provide some
habitat for waterfowl, and the trees and shrubs provide some nesting opportunities for small
birds.
3.1.9 Fauna Associated with the Penney Wetlands
During one of our site visits we recall observing mallard (Anas platyrhycos) and American crow
(Corvus brachyrhyncos). The Penney site likely attracts and supports a number of bird species
typically attracted to western Washington's urban and suburban habitats. Small mammals could
also be present.
There are three listed threatened species reported to be located in the vicinity of the Penney
site. They are Chinook salmon (Oncorhynchus tshawytscha), bull trout (Salvelinus confluentus),
and bald eagle (Haliaeetus leucocephalus). The salmonids are present in the Green River. An
abandoned bald eagle nest was reported about 2 miles southwest of the Penney site (WDFW,
2004).
3,2 Tukwila Pond Site
The Tukwila Pond site is located about 1,000 feet north northeast of the Penney site (Figure 1).
It occupies approximately 24 acres, more than 19 acres of which are open water. The Tukwila
Pond site is bounded by uplands and urban development. Its buffers are narrow, confined to
short steep slopes, and support trees and shrubs. Relatively tall (-75 foot) black cottonwood
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(Populus balsamifera) trees are rooted in the buffer along the east side of the Tukwila Pond site.
The southeast corner of the Tukwila Pond site is the location of the Mitigation site. This area
covers a total of 3.48 acres.
3.2.1 Existing Vegetation
There are five plant communities in the southeast corner of the Tukwila Pond site.
A forest dominated by black cottonwood is located along the eastern perimeter of the Tukwila
Pond site. The southern boundary is dominated by Himalayan blackberry. Both of these plant
communities function as uplands. Most of the Tukwila Pond site is dominated by a monoculture
of reed canarygrass (meadow). A portion of this meadow functions as upland (Figure 3). A
Himalayan blackberry thicket is present at the south end of this upland. A forest composed of
Pacific willow (Salix lasiandra) and red -osier dogwood (Corpus stolonifera) separate the
meadow from the pond proper. The steep slopes of the railroad grade along the southern site
boundary are covered with a tangle of blackberry and the flats with red -osier dogwood in two
places. A depression near the southeast corner of the Mitigation site supports rooted floating
vegetation.
3.2.2 Existing Soils
A 1986 geotechnical engineering report on the Mitigation site described the near -surface soils
as silty fine sand and sandy silt (Dames and Moore, 1986). When Tukwila delineated the
wetlands on the Tukwila Pond site, they described the near -surface soils as silt loam.
3.2.3 Existing Hydrology
Permanent open water is present in the Tukwila Pond site throughout the year. We understand
that the pond is groundwater fed and know that there are seasonal inputs from precipitation and
runoff from adjacent built up areas. On occasion Green River flood water is routed to the pond.
We understand that the pond is relatively shallow, averaging about 2 to 3 feet deep, with the
deepest point about 6 feet below the surface (Partee, 2004). A 1988 construction drawing for a
site to the north indicated a static pond water level of ±13.0 feet (Barghausen, 1988). The same
drawings indicate that the flood elevation is 25.8 feet. In 2005 and 2006 we found the pond
elevation to range from 19.2 to 19.3 feet in April (Table 3).
The elevation of the water in the pond is controlled by a 15 inch corrugated metal culvert (CMP)
fitted with a flap gate located on the east side of the Mitigation site adjacent to Andover. When
the lower Green River is in flood, Tukwila opens the flap gate to allow flood water to enter the
pond for temporary storage. This stored water is released back into the river after the flood
crest has passed (Howat, 2004). The invert elevation of this CMP is18.8 feet (BRH, 2004).
We have observed that a significant portion of the Mitigation site can be flooded during the rainy
season (Figure 3). The southeast corner of the Mitigation site is flooded with water as much as
5 feet deep. Standing water in this depression extends from the area southeast of the upland to
the flap gate CMP (Figure 3). The pond proper floods the western edge of the Mitigation site.
In April 2005 and 2006 we measured the elevation of the pond to be about 19.2 feet (Table 3).
During the same month the elevation of the standing water in the southeast corner of the
Mitigation site was about 18.1 feet in 2005 and 18.4 feet in 2006. Apparently the flap gate CMP
allows the smaller body of water to drain quickly, and retards pond drainage. When the
mitigation area is flooded the surface of the water is covered with pieces of reed canarygrass.
We assume that this flotsam includes reed canarygrass seed.
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3.2.4 Wetland Ratings
There are several Iacustrine wetland classes present on the Tukwila Pond site. A portion of the
proposed Mitigation site is emergent and open water seasonally flooded wetland. To the west is
a forested wetland and beyond that is open water (Cowardin et al., 1979). Based on Ecology's
wetland rating system for western Washington, the wetland present on the Tukwila Pond site is
classified as a Category II wetland (Appendix B).
3.2.5 Wetland Functions
The Tukwila Pond site wetland as a whole, rates at the low end of Category II wetlands (Table
1). It is completely surrounded by impervious surfaces associated with retail and commercial
development. The Tukwila Pond wetland has a good mixture of open water, emergent, scrub -
shrub, and forested wetland habitat, as well as unmanaged upland buffers. Its water quality
functions rate high because it temporarily stores untreated stormwater prior to discharge to the
Green River. It's hydrologic and habitat functions are rated as moderate (Appendix B).
Because the pond is not regularly flushed, is shallow, has a limited outflow, and during the dry
season the size of the pond shrinks, the quality of the water is poor. This is particularly so in the
summer when algal blooms rob the water of oxygen. The pond can be flushed during the rainy
season.
When viewed independently of the Tukwila Pond site, the Mitigation site rates as a Category III
wetland (Table 1). The thick mat of reed canarygrass prevents other species of plants —
including woody shrubs and trees — from becoming established. This persistent monoculture is
unattractive to most animals. It has a moderate rating for water quality because it is covered
solely with herbaceous vegetation. It exhibits moderate hydrologic functionality because it
temporarily stores untreated stormwater during the rainy season. It provides low habitat
functions because of the predominance of the reed canarygrass monoculture.
3.2.6 Tukwila Pond Fauna
Many different animal species have been reported on the Tukwila Pond site. Waterfowl are
attracted to the Tukwila Pond in an otherwise highly urbanized area. It is reported to be used as
permanent habitat for some animals and as a migratory stopover for others (Watershed
Dynamics, 1994). During periods of low water in the fall and winter, mudflats form on the
southern end of the pond. These mudflats provide foraging opportunities for waterfowl. And
the pond provides foraging opportunities for diving birds such as pied -billed grebe (Podylimbus
podiceps) and double-breasted cormorant (Phalocrocorax auritus). During the summer the
limited diversity afforded by thick vegetation limits the value to waterfowl and marsh birds.
Brown bullhead (lctalurus nebulosus) is present in the pond. Few mammals are reported for the
Tukwila Pond site. Muskrat (Onodantra zibethica) haul -out sign was reported in the southeast
corner of the Tukwila Pond site. Bull frog (Rana catesbeiana) is found near the edge of open
water. The only reported priority species on the site is the great blue heron (Ardea herodias).
A report prepared by the WDFW for the Penney site also covers the Tukwila Pond and
Mitigation sites. The WDFW report indicates that no priority species are present on or near the
Tukwila Pond site.
3.3 PRECIPITATION ANALYSIS
As indicated in Section 3.3.2, the surface water elevation of the Tukwila Pond is affected by
groundwater, runoff from surrounding areas, and on occasion flood water from the Green River.
All of these factors are related to precipitation. As shown on Figure 4 the 2004/2005 water
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years was somewhat drier than normal for the first 5 months (October through February),
normal in March and June, and somewhat wetter than normal in April and May (Table 4). The
2005/2006 water year began normally (October and November) but quickly became wetter than
normal in December and January, particularly in January when nearly twice the amount of
expected rain fell on the region (Seattle Times, 2004, 2005, & 2006). The following two months
of the 2005/2006 water year (February and March) were drier than normal and April exhibited a
near normal amount of precipitation.
4. PROBABLE IMPACTS OF THE PROPOSED DEVELOPEMENT
Wetlands have several physical, chemical, and biological processes or attributes that are
important to the ecosystem. These wetland functions include shoreline protection, hydrologic
support, storm/flood water abatement, groundwater exchange, water quality improvement, and
biological support. Each of these functions and the probable impact of site development are
discussed in detail in the following subsections.
4.1 Shoreline Protection
Wetlands provide shorelines protection from erosion caused by tidal action along coasts,
currents in rivers and streams during flooding, and wind or wake generated erosion along
coastlines. Wetlands reduce shoreline erosion by absorbing or dissipating wave energy, by
binding and stabilizing shoreline substrates, and by enhancing suspended sediment deposition
(Hammer, 1992).
None of the wetlands on the Penney site are located adjacent to shorelines. Therefore, filling
these wetlands will have no impact on shoreline functions. We anticipate that limited areas of
soil adjacent to the Tukwila Pond shoreline will be exposed as part of mitigation. As such, a
limited amount of erosion from wave action will likely occur the first couple of years following
construction.
4.2 Hydrologic Support
Hydrology is the single most important factor for establishing and maintaining wetlands and
wetland processes. Hydrologic inputs include precipitation, surface water runoff, groundwater,
tides, and flooding. Water inputs are almost always the major source of nutrients to wetlands.
Water outflows often remove biotic and abiotic material from wetlands. These physiochemical
modifications of the environment have a direct impact on the biotic response in wetlands (Mitsch
and Grosselink, 1986).
During the winter rainy season surface water from Wetland D (one of the Penney site wetlands)
flows into a nearby catch basin. From this parking lot catch basin, water flows through a man-
made storm water conveyance system into a detention pond where it is pumped into the Green
River. The other five wetlands at the Penney site are isolated depressions with no direct
connection to nearby streams. We assume that the water that accumulates in these
depressional wetlands percolates through the soil profile and contributes to the base flow of the
Green River.
Filling the Penney site wetlands will have a minimal impact on the hydrological support function
because the contribution to Green River base flow is extremely small.
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4.3 Storm/Flood Water Abatement
Wetlands can have an effect on the peak flows of floodwaters in streams and on their base
flows during dry periods. Floodwater modification is most often identified with bottomland
hardwood swamps. Forested wetlands in river floodplains can reduce the height of downstream
floodwater peaks by acting as natural reservoirs and directly obstructing and slowing flows. By
retaining stormwater and releasing them at a controlled rate, wetlands augment base flows
(Hammer, 1992).
Tukwila's stormwater management strategy is to release stormwater into the Green River before
flood flow reaches Tukwila. This strategy limits the potential for high water in the river from
blocking runoff generated in the city and reduces the potential for flooding beyond the river's
levees. In support of this strategy, Tukwila will require no detention for the existing impervious
surfaces on the Penney warehouse distribution site, but will require Wig to detain runoff from the
pervious surfaces currently present on this site. The development plan has these pervious
surfaces — which cover 5.8 acres of the Penney distribution site — being converted to impervious
surfaces.
Based on visual observations over a period of two winters, we estimate that the wetlands on the
Penney site provide approximately 16,875 cubic feet (cf) of detention capacity (Table 2). This
capacity assumes that all but one of the wetlands stores water averaging 6 inches deep
throughout the rainy season. It also assumes that standing water represents 100 percent of the
surface area of Wetlands C and D, 75 percent of Wetland A, and 50 percent of Wetlands B and
F. Wetland E is located on a slight slope and retains no surface water.
The wetland mitigation plan includes removing a significant quantity of soil from the Mitigation
site (Figure 5). This action will increase the detention capacity of the Tukwila Pond site by
about 46,900 cf (BRH, 2006).
Using the King County Runoff Time Series (KCRTS) method for estimating runoff, Tukwila will
require 26,200 cf of storage for the additional 5.8 acres of impervious surfaces that will be
created by the Planned Development (BRH, 2004). This is a conservative estimate because the
model assumes that the impervious surfaces are occupied by a mature Douglas -fir
(Pseudotsuga menziesii) forest. The impervious surfaces are actually represented by 0.6 acre
of mowed lawn and 5.22 acres of immature forest and meadow.
The volume of water to be detained on the Planned Development is somewhat less than three
times the stormwater holding capacity of the Penney site wetlands (50,000cf/16,875cf). When
the added capacity on the Mitigation site is also factored into the equation, the increase
stormwater holding capacity of the Planned Development represents nearly a 575 percent
increase over existing conditions (Table 2). Thus the mitigation plan compensates for the lost
stormwater holding capacity of the Penney site wetlands many times over.
4.4 Groundwater Exchange
Groundwater recharge has been shown to occur in isolated wetlands such as prairie potholes,
cypress domes, and floodplain forests. A few wetlands in Wisconsin, North Dakota, and Florida
were shown to have direct connections and contributed significantly to groundwater. But other
wetlands have been shown to have little influence on groundwater or, in some cases, the
wetland is present because of surfacing groundwater (Hammer, 1992).
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It is likely that the Penney site wetlands do not owe their existence to surfacing groundwater.
Rather the precipitation that accumulates in these wetlands seasonally likely contributes to the
regional groundwater system. This phenomenon is thought to be largely due to the original soil
being covered some 35 years ago with up to 10 feet of imported fill soil (Armour, 2004).
4,5 Water Quality Improvement
Wetlands have the ability to remove pollutants from water, through a variety of physical,
chemical, and biological processes. Water purification functions of wetlands are dependent on
four principal components — vegetation, water column, substrates, and microbial populations.
With respect to water quality improvement, the principal function of vegetation in wetlands is to
provide environments for microbial populations. Not only do plants in the water column obstruct
flow and facilitate sedimentation they also provide habitat for microbes. In addition to
attachment surfaces for microbes, substrates provide physical support for plants, and surfaces
for chemical reactions. The water column transports substances and gasses to microbial
populations, carries off by-products, and provides matrix for biochemical processes (Hammer,
1992).
No surface water flows onto the eastern 5.22 acres of the Penney warehouse distribution site.
Only surface water from Wetland D flows off of this area. As such, sediment retention is limited
and most of the water quality improvement capacity of Penney site wetlands is provided by
microbes attached to vegetation and to soil particles. The water flowing from Wetland D
receives some water quality treatment when it flows through grass -lined ditches and is detained
in the regional stormwater pond adjacent to the Green River. The water quality treatment
capacity of the Penney wetlands is 1.16 acres.
The Planned Development specifies treating approximately 14 acres of pollution -generating
surfaces (i.e., asphalt). Surface water runoff from the asphalt will be directed to a water quality
treatment system. The water quality treatment system will be designed and maintained in
accordance with Tukwila engineering standards. The Penney site currently has 7.1 acres of
untreated pollution -generating surfaces (BRH, 2006).
In addition to the water quality treatment system, the Planned Development will have about 1.5
acres of landscaping. Most of the landscaping will be located around the perimeter of the
shopping center. This landscaping represents pervious surface directly connected to the
regional groundwater system. The microbes attached to soil particles in the landscaped areas
will treat water that falls on these areas.
Wig will provide water quality treatment far in excess of that provided by the Penney site
wetlands (Table 2). The water quality treatment system, together with the landscaped areas,
represents about a 1345 percent increase in water quality treatment capacity relative to these
wetlands. The total increase is even larger when the relatively clean water entering the Penney
site wetlands is compared to the water entering the treatment system, which contain petroleum
hydrocarbons and metals.
4.6 Biological Support
Wetlands produce many diverse forms of life and provide habitat for countless others. Wetlands
are dynamic, transitional, and dependent on disturbance. Wetlands receive, hold, and recycle
nutrients continually washed from upland regions. The combined interactions of abiotic and
biotic factors create a diversity and abundance of habitats that make wetlands the most
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important wildlife habitat. Basic productivity of many wetlands far exceeds the most fertile farm
fields (Hammer, 1992).
The Penney site wetlands offer limited biological support functions because they are small and
support immature or simple plant communities. Ducks use the wetlands seasonally during
periods of prolonged precipitation. Other animals likely utilize the wetlands when they are dry.
Filling the Penney site wetlands will have very little impact on the biological support function of
these wetlands. Listed salmonids cannot access the wetlands and bald eagles are not known to
be present on the Penney site. The immature black cottonwood trees on the Penney
warehouse distribution site are too small (<12 inches in diameter and 70 feet tall) to support
nesting and/or roosting bald eagles.
5. MITIGATION APPROACH
After carefully evaluating several scenarios, Wig concludes that filling 1.16 acres of wetlands on
the Penney site is unavoidable. With the exception of the Tukwila Pond site, options for
mitigating for lost wetland functions are limited. In exchange for filling the Penney site wetlands,
Wig proposes to create and/or enhance 3.48 acres of degraded upland and wetland located at
the Tukwila Pond site.
Off -site mitigation makes the most sense in this case because:
• The quality of the existing wetland at the Tukwila Pond site can be substantially
improved (Tablel);
• Both Ecology and the Corps prefer that mitigation occur off site (Appendix A);
• Tukwila's rules allows for off site mitigation;
• Tukwila's Tong -term plans include enhancing degraded portions of the Tukwila Pond
site;
• The Mitigation site is located in the same drainage basin as the Penney site; and
• The Mitigation site is bounded by existing open water and forested wetlands as well
as upland forest and shrub plant communities.
5.1 Code Compliance
5.1.1 Permitted Alterations
Per Tukwila's sensitive area regulations, any use or development of wetlands requires the
review and approval of the Director of Community Development (TMC 18.45.090). Requests
may be approved if the alteration does not adversely affect water quality; fish, wildlife, or their
habitat; drainage or stormwater detention capabilities; lead to unstable earth conditions or
create an erosion hazard; be materially detrimental to any other property; and have an adverse
effect on any other sensitive areas (TMC 18.45.090.6.1). Isolated wetlands exhibiting low
functions that formed on fill material in highly disturbed environmental conditions may be altered
(TMC 18.45.090.B.6). Per these requirements, the Penney wetlands clearly qualify as wetlands
that may be altered (Tukwila, 2005).
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5.1.2 Mitigation Sequencing
Tukwila requires that development proposals demonstrate a reasonable effort to avoid and
minimize impacts to wetlands and their buffers. If avoidance and minimization are not possible,
the preferred order of compensation is:
• Restoring wetlands on upland sites that were formerly wetlands;
• Enhancing significantly degraded wetlands;
• Creating wetlands on disturbed upland sites (TMC 18.45.090.C).
Wig cannot avoid or minimize filling the wetlands on the Penney site because Wig's tenant -
driven key criteria are that the land be at least 18 acres in size and be located on the main strip
of Southcenter Parkway. There are no other properties that meet these criteria.
Wig evaluated off site options including the Macadam site, River Bend site, and a site off of
Strander Boulevard. The Macadam site was too steep and not large enough to be considered a
viable option. The River Bend site was too small and as much as 15 feet of soil would need to
be removed to create wetlands. The Strander site is owned by the Boeing Corporation and is
not readily available for sale. None of these three options represented upland sites that were
formerly wetlands.
The Mitigation site is a significantly degraded wetland with the potential to be enhanced.
Enhancing this degraded wetland is supported by the Corps, Ecology, and Tukwila staff. Here
Wig can create four wetland classes where only one wetland class now exists. Enhancement
will significantly increase the functional value of the degraded wetland.
There is no opportunity to create wetlands on disturbed upland sites in Tukwila.
After evaluating the attributes of four potential mitigation sites, Wig concluded that enhancing
the degraded wetland present on the Tukwila Pond site was the only reasonable available
option. Further, on site mitigation has been discouraged by both the Corps and Ecology
(Appendix A).
5.1.3 Mitigation Plans
Per section 18.45.090.D of the wetland regulations, "wetland and/or buffer relocation may be
allowed only when a mitigation plan clearly demonstrates that the changes would be an
improvement of wetland and buffer quantitative and qualitative functions." Further, the plan
shall "show how water quality, wildlife and fish habitat, and general wetland quality would be
improved."
The close proximity of available degraded upland and wetland adjacent to a large expanse of
open water, scrub -shrub and forested wetland, and upland in an urban environment provide a
unique opportunity to mitigate for impacts to wetlands. The enhanced wetland area will improve
the habitat function of the existing wetland (Table 1) and be composed of four wetland classes —
open water, forested, scrub -shrub, and emergent wetland (Figure 6). The existing Mitigation
site wetland is composed of two wetland classes. The enhanced wetland will be bordered on
the east by upland forest, on the south by wetland and upland shrubs, and on the northwest by
a combination of existing open water and forested wetland. The resultant plant communities in
conjunction with open water will provide excellent habitat for wildlife (Table 5).
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5.1.4 Mitigation Location
According to Section 18.45.090.E of the wetland regulations, on -site mitigation shall be
provided, except where the application can demonstrate that:
a) On -site mitigation is not scientifically feasible due to problems with hydrology, soils,
waves, or other factors; or
b) Mitigation is not practical due to potentially adverse impact from surrounding land uses;
or
c) Existing functional values created at the site of proposed restoration are significantly
greater than lost wetland functional values; or
d) That established regional goals for flood storage, flood conveyance, habitat or other
wetland functions have been established and strongly justify location of mitigation at
another site.
On -site mitigation is not preferred because the Penney site wetlands are very small, surrounded
by asphalt and concrete, and generally isolated from the closest wetland — the Tukwila Pond.
Wig qualifies for off -site mitigation under provisions b) and c). Table 1 demonstrates that the
functional values of the Tukwila Pond site are significantly greater than the function values of
the Penney site wetlands. Further, the Penney site wetland functions can be more than
compensated for by converting degraded upland to wetland and enhancing degraded wetland
on the Tukwila Pond site. Wetland functions currently present on the Mitigation site are
projected to increase from the current rating of a Category III wetland to a Category II wetland
by 2015. When considering wildlife habitat functions in isolation, the created and enhanced
wetland (score = 70) is projected to out perform the existing wetland (score = 15) as well as the
Penney site wetlands (score = 42) (Table 5).
Tukwila requires that off -site mitigation shall occur within the same watershed where the Toss
occurred. The Tukwila Pond site is located in the same basin as the Penney site and therefore
meets this requirement.
Finally, the regulation lists an order of preference for off site mitigation. The Tukwila Pond site
contains existing degraded upland and wetland. Degraded upland areas are listed as the
second and degraded wetlands the fourth preference for off site mitigation. All of the other sites
considered but the unavailable Strander site fall into the third preference. These sites were
deemed unsuitable because they were either too small or contained excess overburden.
5.2 Rationale for Choice
The 24-acre Tukwila Pond site was selected because it is the only suitable area available in the
drainage basin. Also, the degraded area of the Tukwila Pond site has been identified by
Tukwila as an area suitable for enhancement.
Tukwila owns the site.
5.2.1 Case Study
A 6.3-acre monoculture of reed canarygrass in Auburn was converted to a wetland complex
possessing open water, emergent, scrub -shrub, and forested wetland classes (Raedeke
Associates, 2002). This wetland was identified by Ecology as an example of a successful reed
canarygrass conversion project.
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5.2.2 Projected Conditions of the Mitigation Site
At the end of the 10-year monitoring period the monoculture of reed canarygrass currently
present on the Tukwila Pond site is projected to have been transformed into a wetland complex
composed of open water, emergent, scrub -shrub, and forested habitats. All three wetland
functions will improve relative to existing conditions (Table 1). Similarly Wig projects that they
will exceed the functions exhibited by the Tukwila Pond site as a whole (Appendix B). The
improved Mitigation site is projected to enhance water quality and habitat functions largely by
adding complexity and structure where little previously existed. The Mitigation site ten years
after it is improved would rate at the high end of the Category II wetlands.
As shown on Table 1 the restored wetland (Projected Mitigation site) scored higher than the
Tukwila Pond site for habitat largely because of added complexity. The Projected Mitigation site
will have more plant communities and habitat amenities as well as fewer weeds than the
existing Tukwila Pond site.
5.3 Constraints
It appears that potential constraints can be adequately mitigated. The 3.48 acre wetland will be
designed so that seasonal flooding and near -surface groundwater will support and maintain
wetland plant communities. It will be vegetated with native plants that typically tolerate
temporary seasonal flooding during the dormant season.
The plan includes removing reed canarygrass. If the grass were not treated it would create a
maintenance challenge during the monitoring and maintenance period. Its seed will be
distributed throughout much if not all of the Mitigation site during flood events. As such Wig will
remove the reed canarygrass, including its stolon mat, at the time of site grading. The resultant
bare soil will be revegetated with native plants.
A robust monitoring and maintenance plan will limit invading weeds, including reed canarygrass.
Tukwila will protect the Mitigation site in perpetuity. In the event Tukwila alters other parts of the
Tukwila Pond site to enhance its water quality or to increase its capacity to store stormwater, a
deed restriction or some other site development -limiting instrument will protect the enhanced
wetland.
5.4 Goals and Objectives of the Mitigation Plan
To meet Tukwila's no net loss of wetland functions requirement, Wig proposes to improve the
functions of 3.48 acres of degraded wetland and upland on the Tukwila Pond site.
5.4.1 Goals
The goal of the mitigation plan is to create 0.88 acre and enhance 2.6 acres of degraded
lacustrine emergent and open water wetland habitat by converting it to a diverse wetland
complex composed of four wetland classes. This action will considerably improve the habitat for
indigenous and migratory wildlife. It will also increase the stormwater detention capacity of the
Tukwila Pond.
5.4.2 Objectives
Hydrology
• Open Water Wetland — water at least 2 feet deep into the late growing season;
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• Existing Degraded Wetland — seasonally flooded with saturated soil within 12 inches
of the ground surface into the late growing season;
• Emergent Wetland — seasonally flooded with saturated soil within 12 inches of the
ground surface into the late growing season;
• Scrub -shrub Wetland — seasonally flooded with saturated soil within 12 inches of the
ground surface into the middle of the growing season; and
• Forested Wetland — saturated soils within 12 inches of the ground surface in the
early growing season.
Wetland Classes
• Open Water — occupy approximately 0.92 acre;
• Existing Degraded Wetland — occupy approximately 0.88 acre and contain at least 3
native plant species (Table 6);
• Emergent — occupy approximately 0.52 acre and contain at least 3 native plant
species;
• Scrub -shrub — occupy approximately 0.51 acres and contain at least 2 native plant
species; and
• Forested — occupy approximately 0.65 acre and contain at least 2 native plant
species.
Habitat Attributes
• 6 hardwood snags ranging from 10 to 30 feet tall and 6 to 12 inches in diameter; and
• 12 hardwood Togs ranging from 10 to 30 feet long and 6 to 12 inches in diameter.
5.5 Performance Standards
Performance standards provide a basis for measuring the success of the mitigation plan. The
target for meeting the performance standards is within 10 years of installation. Comparing
actual results of the interim monitoring events (i.e., Years 1, 2, 3, 4, 5, 7, and 9) with the
performance standards will determine whether contingency actions are warranted. The
following standards will apply.
5.5.1 Hydrology
• Open Water Wetland — 0.92 acre of open water from 0 to more than 7 feet deep
(constructed bottom 15.2 feet elevation) November through May;
• Existing Degraded Wetland — 0.88 acre of emergent wetland with saturated soil
between 17.7 and 20.0 feet elevation November through June;
• Emergent Wetland — 0.52 acre of emergent wetland with saturated soil between 17.2
and 17.7 feet elevation November through June;
• Scrub -shrub Wetland — 0.51 acres of scrub -shrub wetland with saturated soil
between 17.7 and 18.2 feet elevation November through May; and
• Forested Wetland — 0.65 acre of forested wetland with saturated soil between18.2
and 19.2 feet elevation November through April.
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5.5.2 Soil
At final grade, the upper 6 inches of soil will contain 20 to 25 percent organic matter, as
validated by an approved agricultural testing laboratory. This requirement will be
reflected in final plan specifications.
5.5.3 Vegetation
• Emergent Wetland — 0.52 acre of emergent wetland that contains at least 3 or more
native emergent plant species each consisting of at least 20 percent of total native
emergent plant cover. The total native emergent plant cover will be at least:
• 5%inYear 1,
• 25% in Year 2,
• 30% in Year 3,
• 40% in Year 4,
• 50% in Year 5,
• 70% in Year 7,
• 80% in Year 9, and
• 90% in Year 10.
• Existing Degraded Wetland — 0.88 acre of emergent wetland that contains at least 3
or more native emergent plant species each consisting of at least 20 percent of total
native emergent plant cover. The total native emergent plant cover will be at least:
• 5%inYear 1,
• 25% in Year 2,
• 30% in Year 3,
• 40% in Year 4,
• 50% in Year 5,
• 70% in Year 7,
• 80% in Year 9, and
• 90% in Year 10.
• Scrub -shrub Wetland — 0.51 acres of scrub -shrub wetland that contains at least 2 or
more native shrub plant species each consisting of at least 20 percent of total native
shrub plant cover. The total native shrub plant cover will be at least:
• 5%inYear 1,
• 20% in Year 2,
• 30% in Year 3,
• 40% in Year 4,
• 50% in Year 5,
• 70% in Year 7,
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• 80% in Year 9, and
• 90% in Year 10.
• Forested Wetland — 0.65 acre of forested wetland that contains at least 2 or more
native tree plant species each consisting of at least 20 percent of total native tree
plant cover. The total native tree plant cover will be at least:
• 5%inYear 1,
• 10% in Year 2,
• 15% in Year 3,
• 20% in Year 4,
• 30% in Year 5,
• 70% in Year 7,
• 80% in Year 9, and
• 90% in Year 10; and
• No more than 20 percent of the vegetation will consist of non-native invasive plant
species at any time during the monitoring period. This includes Himalayan
blackberry, reed canarygrass, purple loosestrife (Lythrum salicaria), and all other
Class A, B, and C weeds on the state noxious weed list.
5.5.4 Structure
• Emergent Wetland — vegetation ranging from 1 to 4 feet tall by Year 3;
• Existing Degraded Wetland — vegetation ranging from 1 to 2 feet tall by Year 3;
• Scrub -shrub Wetland — vegetation ranging from 4 to 8 feet tall by Year 5; and
• Forested Wetland — vegetation ranging from 8 to 20 feet tall by Year 7.
6. CONSTRUCTION PLAN
This section of the plan describes the strategies that will be used to achieve the objectives
described in Section 5.4.2.
The plan is to remove all of the reed canarygrass and replace it with native trees, shrubs, and
herbs adapted to seasonally flooded and saturated soil conditions. We reviewed the file, visited
the site, and interviewed the designer of what appears to be a successful reed canarygrass
conversion project in the City of Auburn. As indicated in Section 5.2.1, the 6-1--acre Goedeke
wetland enhancement project was transformed from a monoculture of reed canarygrass to a
diverse wetland composed of four wetland classes. To achieve this result, the reed canarygrass
was mowed and the stolon mat was excavated, buried and covered with fabric and soil. In 2004
this precipitation driven wetland contained a wide variety of native trees, shrubs, and herbs, with
very little reed canarygrass. Based on results of the Goedeke project, it appears that the reed
canarygrass can successfully be converted to a wetland complex possessing increased water
quality, hydrologic, and habitat values.
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6.1 Hydrology
Wig installed 14 shallow groundwater monitoring wells and 2 staff gauges in late 2004 to
characterize the hydrology of the Mitigation site. Based on April measurements the central
ridge of the Mitigation site is upland covering 0.88 acre (Figure 3). A significant portion of the
area surrounding the upland is flooded in the winter and spring. The flooded area west of the
upland drains slowly, presumably because the flap gate CMP is small relative the volume of
water in the pond proper. We believe that the flooded area east of the upland drains more
quickly because it represents a much smaller volume of water.
6.2 Soils
Wig will grade the finished elevation of the Mitigation site according to the grading plan prepared
by BRH (Figure 5). The grading plan is based on the results of the groundwater monitoring
program during April 2005 & 2006. At a minimum, the upper ±6 inches of soil will be excavated
and exported. Exporting the upper layer of soil removes the canarygrass' subsurface
reproductive parts. More than a 6-inch-deep scoop will be required to eliminate reed
canarygrass' subsurface reproductive parts on occasion.
Wig will take every precaution to avoid or minimize impacts to existing stormwater control
structures, including the flap gate CMP. If the flap gate and/or the associated berm are
disturbed, Wig will repair these structures to Tukwila standards. We understand that the
Tukwila Pond is considered a jurisdictional wetland by the Corps. As such a permit to export
soil from the Mitigation site and if necessary import topsoil onto the same will require a permit
from the Corps (Whiting, 2006). With respect to Wetland D on the Penney site, Wig must notify
the Corps within 30 days after it is filled (Appendix A).
Wig will match grades along the edge of the existing forested and scrub -shrub wetlands, the
edge of the pond, and/or the upland buffers to the south and east. The slopes of the excavated
channel will be nearly vertical. The intent is to encourage fish and wildlife that are attracted to
open water to utilize these habitats and discourage emergent vegetation. Our hope is that the
channel will promote water circulation from the Tukwila pond. The flow and the resultant mixing
action could help improve the quality of the water in the Tukwila pond. To facilitate this flow,
Wig will excavate the edge of the Tukwila pond at the entrance to the channels to match the
bottom elevation of the channel.
To augment the organic content of soils subject to excavation, Wig will rotovate three inches of
fertile mulch (organic compost) into the upper 8 inches of the subgrade as necessary.
6.3 Vegetation
As shown on Figure 6, at least four wetlands classes are proposed — open water, forested,
scrub -shrub, and emergent. These new wetland classes will be juxtaposed with three existing
wetland classes and two upland classes. The existing open water, scrub -shrub, and forested
wetland classes and upland plant communities have been incorporated in the design to
compliment the created/enhanced wetland area.
Wig will vegetate the Mitigation site as indicated in Table 6. Several of the herbaceous plant
species will be broadcast seeded throughout the emergent, scrub -shrub, and forested habitats.
Larger herbs will be installed in the emergent wetland between 17.2 and 17.7 feet elevation.
Selected herbs and the indicated shrubs will be installed in the scrub -shrub wetland between
17.7 and 18.2 feet elevation. The forested wetland will be vegetated with herbs, shrubs, and
trees between 18.2 and 19.2 feet elevation. A mixture of grass species will be broadcast
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seeded throughout the Existing Degraded Wetland. The seed will be covered with about'/ inch
of soil to minimize the potential for the seed to float away during subsequent flood events.
Mulch will be placed around the base of all installed trees and shrubs for weed control and
moisture retention in the spring after the threat of flood has past.
Wig will install a temporary irrigation system designed to deliver up to 1 inch of water per week
in the mitigation area for at least one growing season after the plants are installed.
6.4 Habitat Structures
Wig will place 12 medium-sized (6 to 12 inches in diameter and 10 to 30 feet long) hardwood
Togs on the Mitigation site as habitat amenities. To reduce the potential for these logs to float
away during anticipated periods of high water, Wig will anchor the logs to the ground. Wig will
also install 6 hardwood snags — ranging from 10 to 30 feet tall and 6 to 12 inches in diameter on
the Mitigation site.
6.5 Installation Sequence
During a pre -construction meeting, the grading contractor, Wig, the project biologist, and
appropriate regulatory agency staff will review the grading plan and best management practices
(BMP), including stormwater pollution prevention plans (SWPPP), temporary erosion and
sediment control plans (TESC), and spill control and prevention plans. In addition, components
of the mitigation plan will be reviewed with the landscaping contractor at this meeting.
Based on the outcome of the pre -construction meeting, the grading contractor will flag the
construction limits consistent with the grading plan and BMPs, and will install temporary filter
fabric fences as necessary. A temporary fence will also be installed between the construction
area and the Sitka willow trees along the northwest boundary of the Mitigation site. Temporary
fence will also be placed around existing clumps of red -osier dogwood shrubs along the
southern Mitigation site boundary.
Track hoe excavators, dump trucks, and/or dozers will be used to grade the Mitigation site.
Machines will enter and leave the site via temporary construction entrances off Andover
Parkway West. Because road drainage may contain soil and mud from construction vehicles
and since the associated catch basins ultimately discharge to the Green River, filter fabric
sediment traps will be installed and maintained at each catch basin. In addition, Andover will be
swept as dirt or mud accumulates. Dust abatement measures, such as site watering during
grading, will be instituted as necessary.
As indicated previously, prior to site grading the reed canarygrass will be mowed and the
cuttings will be disposed off site. Following mowing the reed canarygrass mat will be excavated
and exported. If the results of the soil chemical analysis indicate that organic augmentation is
warranted, approximately three inches of fertile organic mulch will be rotovated into the upper
top 8 inches of soil.
Next the contractors will install the habitat amenities, the temporary irrigation system, fence,
sign, etc.
In the spring after floodwaters have subsided, seed from residual weedy plants that likely are
distributed over most of the Mitigation site will sprout. As such the landscaping contractor will
likely have to treat the Mitigation site for weeds prior to planting. After the weeds are treated the
landscaping contractor will broadcast seed the Mitigation site that is not designated open water
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habitat. About'/2 inch of soil will be raked over the seed. Landscapers walking all over the site
will also help "set" the seed. Following seeding the landscaping contractor will install the plants
specified on Table 6.
Following construction and plant installation, the project biologist and landscaping contractor's
representative will meet with Tukwila staff to develop a punch list of deficiencies. After the
punch list items are addressed by Wig, Wig will seek approval for concluding the construction
phase of the mitigation plan and seek Tukwila's approval to initiate the start of the ten-year
monitoring period. Wig will develop an as -built plan that will be used as a basis for evaluating
future results.
7. MONITORING PLAN
The purpose of the monitoring plan is to assess the existing Mitigation site and the results of the
mitigation measures. Monitoring the water regime prior to final design and construction
increases the probability of success. Post -construction monitoring provides an index for
measuring the performance of the mitigation plan, the extent and timing of remedial actions (if
necessary), and ultimately the length of the monitoring period. The monitoring plan consists of
three separate but equally important steps; pre -construction monitoring, construction monitoring,
and post -construction monitoring.
7.1 Pre -Construction Monitoring
Wig has been monitoring the hydrology of the Mitigation site since October 2004.
7.2 Construction Monitoring
Wig will maintain quality assurance by monitoring grading and landscaping contractors during
construction. This aspect of the monitoring plan is particularly important because the final
design elevation of the wetland is critical to establish and maintain the appropriate wetland
hydrology. Similarly the methods and techniques used to install the plants are important
because in many cases survival is dependent on the quality of the installation.
Tukwila will be responsible for final approval of construction. Wig will consult with Tukwila to
assess deviations from the approved plan. After construction is completed, Tukwila will
evaluate the installation and develop a punch list as necessary. Wig will address punch list
items and prepare a post -installation report for review and approval by Tukwila. The post -
installation report will be the basis for comparing future monitoring reports.
7.3 Post -Construction Monitoring
Hydrology monitoring will commence immediately following construction to characterize the
modified hydrologic conditions. The pre -construction shallow groundwater monitoring wells and
staff gauges will be replaced and incorporated as part of the post -construction monitoring plan.
Their position will be located by survey and shown on the As -Built Plan.
Wig will monitor the mitigation area for 10 years following installation. A qualified biologist will
be engaged for this effort. To document the results of the mitigation measures and to ensure
that reed canarygrass and other incompatible weeds do not invade and take over the Mitigation
site, Wig will monitor the Mitigation site annually for the first 5 years following installation as well
as in Years 7, 9, and 10. Post -construction monitoring will include hydrology monitoring as well
as vegetation monitoring. Wig will submit a detailed report comparing actual versus expected
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performance standards to Tukwila for review and approval by December 31 each year the
Mitigation site is monitored.
7.3.1 Hydrology
Wig will measure the water levels at least four times a year (April, May, June, and August)
during the growing season with an electronic water level meter.
7.3.2 Soils
Wig will not monitor soils after post -installation sampling, provided that the performance
standard is met at that time.
7.3.3 Vegetation
To measure the success of the vegetation effort, Wig will install permanent photographic and
vegetation monitoring points in the Mitigation site. The monitoring points will be established by
installing a permanent structure such as rebar, wood, fence post, plastic pipe, etc. Wig will
characterize the vegetation in August in 1/100-acre circular plots. The monitoring biologist will
also informally assess the vegetation when on site to monitor hydrology. The intent of informal
vegetation monitoring is to identify areas where undesirable weeds (e.g., reed canarygrass,
purple loosestrife, etc.) are present. These observations will be relayed to the maintenance
contractor for timely removal action. Photographs will be taken facing a predetermined direction
for consistency to provide a visual record of the Mitigation site throughout the monitoring period.
The vegetation monitoring will assess:
• Species composition;
• Percent cover of each plant stratum and species;
• Stand height; and
• The health of the vegetation.
7.3.4 Fauna
Wig will record site observations of fish and wildlife during vegetation and groundwater
monitoring activities.
7.3.5 Habitat Structures
After the habitat amenities are installed and their location noted on the As -Built Plan, it will not
likely be necessary to monitor them again. However, as indicated in Section 5.4.4, Wig will
characterize the average height of the plants present in the emergent, scrub -shrub, and forested
habitat types. Wildlife habitat is determined by the interspersion of plant communities, by the
structure of the plant communities, and by the mixture of species within a community. Although
all of these are important, most species of wildlife respond more to structure of the plant
community than to the plant species making up a community (Hall, et al., 1985).
7.3.6 Water Quality
Wig will not monitor water quality.
7.3.7 Buffers
Wig will not monitor the buffers.
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8. SITE PROTECTION
To discourage human intrusion, a permanent post -and -rail fence at least 4 feet tall will be
installed along the eastern boundary of the Mitigation site adjacent to Andover Parkway West.
The eastern and southern perimeter of the Mitigation site will be posted with Habitat
Conservation Area signs (Figure 6).
Tukwila will be responsible for protecting the Mitigation site. In accordance with Section
18.48.090.0 of the sensitive areas regulations, the Mitigation site shall remain undeveloped and
be protected from development in perpetuity. As such, Tukwila shall protect the Mitigation site
via deed restriction, conservation easement, or other legally binding instrument. After Wig's
monitoring and maintenance obligation is completed, the installed vegetation should be
protected against any impacts from mowing, cutting, dredging, or other adverse activities to the
Mitigation site.
9. MAINTENANCE PLAN
Wig will maintain the Mitigation site during the 10-year monitoring period. Maintenance includes
irrigating recently installed plants to promote their establishment and survival. One inch of water
per week shall be applied to the Mitigation site from the time the plants are installed to mid -
September the first year of plant installation. Irrigation is not required in subsequent years.
Maintaining the Mitigation site is paramount to prevent unwanted plant species — particularly
reed canarygrass and purple loosestrife — from expressing dominance during the 10-year
monitoring period. Maintenance measures beyond the required monitoring period will become
the responsibility of Tukwila.
In addition to collecting hydrologic and vegetative data as specified in Section 7.3, the
monitoring biologist will also note physical and biological features on the Mitigation site that
need attention, are of note, or reflect the ecological health of the mitigation area. These
features include, but are not necessarily limited to, wildlife use, trash, plant mortality, weeds,
and predation by herbivores, etc.
When reed canarygrass, purple loosestrife, or another aggressive undesirable weed is
observed, Wig will instruct the maintenance contractor to treat the offending plants within 14
days. Manual weeding is the preferred method for removing the plants. However, on occasion
it may be necessary to spot spray clumps with an approved herbicide. Rodeo is an herbicide
approve for use in aquatic environments
10. CONTINGENCY PLAN
Wig recognizes that there is a chance that some of the installed plants will not survive the
seasonal flooding typical of the Tukwila pond. Wig also recognizes that seasonal flooding tends
to favor reed canarygrass. To reduce these potentials Wig will:
• Post a bond sufficient to cover the cost of replanting the Mitigation site;
• Install plants that tolerate seasonal flooding during the dormant season;
• Monitor the installed plants annually for the first 5 years;
• Remove all reed canarygrass and purple loosestrife plants present on the Mitigation site;
and
• Install new plants annually to replace those that expired.
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10.1 Post a Bond
As indicated in Section 12, Wig will provide Tukwila with a surety instrument in the amount of
150 percent of the estimated cost to install plants on the mitigation site.
10.2 Install Plants Suited to Seasonal Flooding
Wig will install plants native to Western Washington that are adapted to seasonal inundation
during the winter rainy season. Many wetland plants survive seasonal inundation during the
winter rainy season because these plants are dormant at the time of flooding. As indicated on
Table 6 these plants include:
• Trees - black cottonwood and Oregon ash (Fraxinus latifolia), and to a limited extent red
alder (Alnus rubra);
• Shrubs - Pacific willow, Piper's willow (Salix hookeriana), Sitka willow (Salix sitchensis),
black twinberry (Lonicera involucrata), Pacific ninebark (Physocarpus capitatus), and
red -osier dogwood; and
• Herbs such as slough sedge (Carex obnupta), tufted hairgrass (Deschampsia
cespitosa), common spike-rush (Eleocharis palustris), wool -grass (Scirpus cyperinus),
and reed mannagrass (Glyceria grandis).
The Mitigation site can be subject to flooding events during the rainy season. We observed
inundation in both 2005 and 2006. The duration of these events can be as long as 4 months.
The plants selected to replace reed canarygrass typically survive short -duration inundation
during the winter rainy season when plants are typically dormant.
10.3 Annual Monitoring for the First 5 Years
Plant succession on bare ground is fairly predictable. A number of weeds, including reed
canarygrass, are expected to invade the bare areas initially. Bare areas are common on
mitigation sites the first couple of years following plant installation. That is, bare soil is typical
between installed trees and shrubs as well as locally where seeded grasses and herbs are
removed by herbivory, flowing water, etc. To minimize the potential for reed canarygrass to
become established in these bare areas, Wig will monitor the mitigation site several times a
year (April, May, June, and August) during the first 5 years following plant installation.
10.4 Remove All Reed Canarygrass
If reed canarygrass (and purple loosestrife) is observed during monitoring visits by the project
biologist, its location will be marked in the field by the biologist. Initially, the biologist will
accompany the maintenance contractor when they treat the offending plants to ensure that all of
these plants are treated. Once the biologist feels comfortable with the maintenance contractor's
ability to identify and treat offending weeds, it will no longer be necessary to accompany the
maintenance contractor when weeds are observed. Wig will make every attempt to treat
volunteer reed canarygrass plants before they go to seed. The entire plant, including stolons
will be treated. This action will increase the potential that reed canarygrass plants represent a
small fraction of the plant community.
10.5 Install Additional Plants as Necessary
Typically 80 percent of the installed trees and shrubs survive installation. As such, Wig
assumes that installing additional trees and shrubs and quite possibly herbs will be necessary
near the end of the first growing season. If during subsequent years the monitoring biologist
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concludes that additional plantings are required, Wig will install additional plants as necessary.
The selected replacement plants will include the most robust plant species growing on the site
at the time of site evaluation.
11. SCHEDULE
Wig anticipates executing the construction plan in 2007 and upon receipt of permits and/or
approvals from Tukwila and/or Ecology. Site grading will be limited to the drier months when
groundwater elevations are at their lowest. Wig anticipates installing the plant material the
following spring after flood waters have subsided. It is important that the surface soil (i.e., upper
12 inches) is moist at the time of plant installation. Monitoring will commence immediately
following acceptance of plant installation by Tukwila.
12. PERFORMANCE BOND
Wig will post a bond or other surety in the amount of 150 percent of the value of the expected
cost to install plants on the Mitigation site.
13. LIMITATIONS
Work for this project was performed, and this plan prepared, in accordance with generally
accepted professional practices for the nature and conditions of the work completed in the same
or similar localities, at the time the work was performed. It is intended for the exclusive use of
Wig Properties LLC-SS and its assigns for specific application to the referenced property. This
plan is not meant to represent a legal opinion. No other warranty, express or implied, is made.
It should be noted that Chad Armour, LLC relied on information provided by others indicated
previously. Chad Armour can only relay this information and cannot be responsible for its
accuracy or completeness. Also note that wetland mitigation planning is an inexact science.
Biological professionals may disagree on the nature and extent of mitigation plans. Final
acceptance of this wetland mitigation plan is the responsibility of the permitting authority.
Accordingly, this wetland mitigation plan should be reviewed by the appropriate permitting
authority prior to committing to detailed planning and design activities.
C:/Jobs/Wig/Revised Final Wetland Mitigation Plan.doc24
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08/10/06
56
Chad Armour, LLC
August 25, 2006
Moira Bradshaw, Senior Planner
City of Tukwila Department of Community Development
6300 Southcenter Boulevard, Suite 100
Tukwila, Washington 98188-2544
Subject: Mitigation Plan Bond
Southcenter Square
Tukwila, Washington
SEP 2 2 2006
T UKWII A
PUBLIC WORKS
Dear Ms. Bradshaw:
In your August 22, 2006 email you asked us to estimate the cost to construct and restore the
wetland in the Tukwila Pond and to monitor and maintain it for 10 years,
We trust that this information meets your needs. If you have any questions about the
spreadsheet, please let us know.
Sincerely,
Chad Armour, LLC
Chad Armour
Principal
Attachments:
Attachment A — Bond Quantity Worksheet for the Tukwila Pond Wetland Restoration
6500 1261h Avenue SE
Bellevue, Washington 98006
www.chadarmour.corn
(425) 641-9743
(425) 643-3499 (Fax)
chadSchadarmaur.com
Pu1o6-gal
57
Bond Quantity Worksheet for Sensitive Area Mitigations
Project Name:
Southcef'ier Square Project Address: Tukwila Pond Wetland Restoration Wetland File No.
23-Aug-06 Contact Person/Phone: Chad Armour (425.641.9743)
Date:
Trees (includes delivery, installation, and materials)
Scientific Name Common Name I Qty Unit Price
1 gallon
Alnus rubra
Fraxinus lataolia
Pop:dustrichocarpa
re• alder
regon as
!black cottonwood
[Total
o
50.0
Qty
Unit Price
2 gallon
2 gal i Qty Unit Price 1.5"* salt Total Cc
Total I 1.5" cal Total
a1. v 4 ». u I ,)> -,)aD
$6. of 31 $ 55.00 $1,705 51,705
� OS
s0.00
(Total
50.00
Total
$6,875f S6,875
Shrubs (includes delivery, installation, and materials)
Scientific Name Common Name I Qty Unit Price
1 gallon
:era i
1er8
Pi
a
at
Live Stakes / Cuttings
Scientific Name
Populus trichocarpa
Salix lasiandra
Salix piperi
Salix sitchensis
d-osper dogwooa
black twinberry
Pacific ninebark
Common Name
ty
otaI
Unit Price
Slack cortoraw
Pacific willow
Piper's willow
Sitka willow
440 $2.00
1 gal
Total
au. 3.56 I a s .uu fu,i40 0- j av vu aau air.
0.00I 30 ) 5 30.00 I 5900.00 ( I $0.00 $9a00 UO
$1 Cho
OAQI$900
_ 30 1 $ 30AG ' s9GU.0U� � $0.00
i I SI1,94'O,tlil
s0.001 !Total I_ $11,940.001 'Total T sue,
Cost
Unit
Qty Unit Price I 2 gal
2 gallon Total
Total. Cos
50.00
5�
124 52.00 s24
123 $2.001
Sub Total $1,374.00
Qty
Unit Price 5 gal
5 gallon I Total
Page 1 Bond Quantity Worksheet.xls
58
Earthwork/Organics (labor, equipment, overhead and profit)
S , ecific Name 1 Unit Price
Gradin
Topsoil - delivered & spread
Mulch
14.0
Unit
40
Amount
4, 0
Ttstal
$3.00
4000
$12.951 1400
$20.001 681
4.000
1.400
681
4 2,000.,00
Sub Total
Grasses/Emeraents (includes delivery, installation, and mater'als)
Name Seeding Acre Unit Pounds Total Cost.
Rate Price
,10 . 2..25 ,7
Land See cax, including:
Beckmannia syzigachne
Deschanrpsiia cespitosa
flymus glaucus
Giyseria occtdentalis
Hordeatm brachyantherurpr
2 to 40 lb./acre
American slou&hgrass
tufted hairgrass
blue wildrye
westem mannagrass
meadow barley
ap is cespitosa
crophyllurn
rra rarults
ufted hairgrass
large -leaved avens
reed mannagrass
1.68 $50.00; 0.55
1.68 S120.001
1.68 $100.00 5.9
$27.50
$120.00
$590.00
Sub Total
53,465.50
Specific Name
Qty
Unit
Price
br
Total Cost
Carexobnupta 'slough sedge
1 ,
lsawbeak sedge2
7436
$1.65
'
$x2,269.40'
,ar°ex stipata
B1eod.hrax ahustris [common spike-rush
1898
$1.65
1.31 40
5cirpaus oypchinus Iwool-grass
950
$1.65
$,13 ,70
bcrrpars da2rerraxrernarretarai lsoftstem bulrush
950
$1.65
$1„56+.50
$0.00
Sub Total
$30,150.45
Page 2
111.30.00
1',620.00
S99,750,.00
Bond Quantity Worksheet.xls
59
Habitat Structures (includes delivery, installation, and materials)
Specific Name Unit
Price
Wood debris, large
Snags
General Items (includes delivery, installation, and
Specific Name
Fencing, Split Rail, 4' High (3-rail) or 3' High (2-rail)''
Signs, Sensitive Area Boundary
Irrigation, Temporary
s350.00
S500.00I
12
0
Sub Total $7,200.00
materials)
1 Unit Cost 1 Units 1
1 $10.001 8b0 I
I 320.001 12
1 S9,500.001
1 _I
Sub Total
** may be included in construction bond instead of wetland bond with City approval
Monitoring and Maintenance Costs
tenance - next 8 years
Monitoring attauruta1 -Est 5 years
Mormon annual - Year 7
Monitoring annual - Years 9 & 10
O
Unit Prices- Unit
LI I
I8 1 5,650.001
5 2,500.001
1 1 1 3,000.001
1 2 1 3,500.001
Sub Total
Total Construction/Maintenance/Monitoring Costs
Total Bond Amount Agency Multiplier
150%
1 Cast
6,000 Off
$240.00
,500.00
515,740.00
Total Cosa ~
526,366.004
S45,200.00
$12,500 00
0.00
$7
594,066.00
S26.9,186, 95
$4
9,43
• Page 3
Bond Quantity Worksheet.xls
60
6500 128a" Avenue 3.IE.
lievue, 'Washington 98006-39411
(425p 841 9"743 Office (425) 43•34 99 Fax
chadir arc hadar'mour.com
August 13, 2010
Job No. 08-002
Ms. Anjali Wig
Wig Properties LLC-SS
4811 — 134mh Lace SE.
Bellevue, Washington 98006
Subject: Third Year Wetland Mitigation Monitoring Report
Tukwila Pond Mitigation Area (Fed Ref No. 200601027; St Ref No. 3815)
Tukwila, Washington
Dear Ms. Wig:
We are pleased to present the results of our wetland mitigation monitoring report the
third year after installing plants on the above -referenced property. This is the third of
several monitoring reports to assess the condition of the mitigation area relative to the
performance standards. The purpose of the work is to satisfy federal, state, and local
wetland permit requirements.
The report is organized in sections and includes:
SUMMARY OF FINDINGS that presents the results of the third year of monitoring
and recommendations for additional work;
BACKGROUND INFORMATION that explains the purpose for the mitigation and
how the mitigation area came to be;
MONITORING METHODS that describes how we collected the data, and presents
the goals and performance standards of the mitigation plan;
MITIGATION AREA OBSERVATIONS that presents the results of our current
hydrological and vegetative observations;
CONCLUSIONS that summarize the results of wetland mitigation to date relative to
the performance standards; and
LIMITATIONS of this project.
Tables, figures, and representative photographs follow the text of the report. Table 1
shows the precipitation that fell on the region in the 2009/2010 water year. Table 2
presents the hydrological data for the mitigation area. Table 3 presents the vegetative
data for the various wetland classes. And finally Table 4 summarizes the current
vegetative data relative to the performance standards. Figure 1 is a vicinity map that
shows the location of the mitigation area. Figure 2 shows the location of the vegetation
classes, monitoring wells, and other pertinent features, as well as the size of the wetland
classes and the plants that were installed on the mitigation area. Representative
photographs follow the figures.
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Third Annual Wetland Mitigation Monitoring Tukwila Pond Mitigation Site
Tukwila, Washington
SUMMARY OF FINDINGS
Wig Properties, LLC-SS (Wig) converted the area east of the Tukwila Pond from a
wetland and upland plant community dominated by reed canarygrass to a wetland plant
community containing four wetland classes — open water, emergent, scrub -shrub, and
forested. During the grading operation Wig was able to retain a significant portion of the
mature trees and shrubs present in and adjacent to the mitigation area (site). Soon after
the site was graded Wig installed several thousand native trees, shrubs, and herbaceous
plants. Wig also applied the seed of several different grasses and herbs to the site.
Chad Armour, LLC (Armour) collected groundwater data from several shallow
groundwater monitoring wells several times in the spring and summer and collected
vegetative data in the summer of 2010.
The results of the third year of monitoring indicate that the site is in the process of
complying with the performance standards. It appears that wetland hydrology is present
throughout most of the site. The monitoring well measurements that are out of
compliance appear to be related to excess ground elevation. Most of the vegetative
performance standards are in compliance at this time. Currently the dominant plant
species include Pacific willow, Sitka willow, red -osier dogwood, and tufted hairgrass.
We observed less than 1 % cover of non-native invasive plant species.
Recommendations
We recommend that Wig continue to aggressively treat non-native invasive plant
species, particularly reed canarygrass and purple loosestrife. The reed canarygrass and
purple loosestrife should be removed from the ground, roots and all and disposed off of
the site. However; the reed canarygrass is prevalent enough that the clumps can be
sprayed with an approved herbicide.
Install up to 25 Oregon ash trees in the forested wetland near where red alder and/or
black cottonwood trees have died. Installing `large' trees is not beneficial. Rather the
new trees should be of the 5-gallon variety.
Fit the existing `large' trees and the 25 trees to be installed with tree trunk protectors.
The tree trunk protectors will make it difficult for rodents to access the bark of these
trees. It will be necessary to remove the grass before the protectors are installed.
Remove the wooden stakes that were installed to support the `large' trees. These trees
no longer need the support.
Remove any remaining irrigation pipe on the site.
BACKGROUND INFORMATION
Wig constructed a wetland and enhanced degraded wetland in 2007 to compensate for
filling slightly less than 1.16 acres (ac) of wetland on their Tukwila Southcenter shopping
center. The 3.48ac site is a part of a larger 24-ac Tukwila Pond property that includes
the pond and what was once a field of reed canarygrass, both with fringes of willow
and/or black cottonwood trees. The site is located west of Andover Parkway West about
600 feet (ft) south of the intersection of Strander Boulevard and Andover Parkway West
in Tukwila Washington (Figure 1 — Tukwila Pond Site).
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Third Annual Wetland Mitigation Monitoring
Tukwila, Washington
Tukwila Pond Mitigation Site
Upland was transformed to wetland and degraded wetland was improved by replacing
non-native invasives with a native plant assemblage. First Wig mowed the reed
canarygrass then removed its rhizome mat before hauling it from the site. Then they
removed some soil from the site, bringing the surface closer to the seasonal water table.
To boost post -grading soil productivity, Wig mixed 3 inches (in) of Steergrow, a top soil
substitute, into the upper layer of soil. They then installed several snags and added
several pieces of large woody debris (LWD) to the finished surface prior to installing the
plants.
At the time the mitigation area was graded, Wig made every effort to avoid cutting down
existing mature trees and shrubs. The net result is more forested wetland and less
emergent wetland that planned. The City of Tukwila (City) was concerned that the
Steergrow (50% steer manure and 50% sawdust) would negatively impact the water
quality of the Tukwila Pond. For this reason the City asked Wig to bridge the open water
channel to prevent the water in the channel from mixing with the water in the pond. The
sand dike at the south end of the channel has been breached and water from the pond
has been comingling with water in the channel for the last two rainy seasons. Wig also
added a berm adjacent to the northwest edge of the mitigation area.
Following grading, Wig installed several thousand trees and shrubs. Wig also installed
several thousand sedge, rush, and spike-rush plugs as well as a mixture of emergent
plant seeds to the bare soil. The plan was to install plugs and seeds differentially among
wetland classes. During installation the plugs and seeds were installed across the entire
wetland mitigation area.
Prior to construction Armour installed 17 shallow groundwater monitoring wells (wells)
made from plastic PVC pipe across the site to model the groundwater elevation (Figure
2). Ten of these wells survived site grading. The seven new wells replace those lost
during site grading. Together they completely cover the site.
The wells serve as the centers of 13 circular 1/100 acre vegetation assessment plots.
After the first years monitoring we noticed that some wells yielded plots that straddled
vegetative classes (i.e., emergent and forested). In other areas large branches of
willows fell into plots, causing an emergent class to look like a forested class. For these
reasons we moved five of the vegetative plots about 20 to 75ft from the similarly
numbered well.
For the past two years Wig has maintained the site by removing non-native noxious
weeds. Weeds removed and/or treated include Himalayan blackberry, reed
canarygrass, and purple loose -strife.
In 2008 Wig installed about 80 additional willow live stakes on the site to replace those
that had died.
MONITORING METHODS
Armour used an electronic water level indicator to detect ground and/or surface water in
each of the 17 wells five times (March, April, May, June, and August). These
measurements allow us to calculate the elevation of the groundwater or surface water.
Groundwater elevation can be used as a surrogate to infer surface soil saturation. In
this instance we assume that wetland hydrology is present if groundwater is within 1ft of
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Third Annual Wetland Mitigation Monitoring
Tukwila, Washington
Tukwila Pond Mitigation Site
the surface or the surface soil is saturated. We record the data in the field and transfer it
to a spreadsheet that calculated the ground and/or surface water elevation.
In each vegetative plot we note the health, estimated the cover of the trees, shrubs,
herbs, and undesirable plants by species, and estimated the height of the vegetation.
We designed the performance standards to evaluate short-, mid-, and long-term
vegetation targets. Armour assessed the vegetation on August 11, 2010; recording the
data in the field and transferring the data to an electronic spreadsheet for analysis.
Goal
The goal of the mitigation plan is to create 0.88ac and enhance 2.6ac of degraded
lacustrine emergent and open water wetland habitat by converting it to a diverse wetland
complex composed of four wetland classes. This action will considerably improve the
habitat for indigenous and migratory wildlife. It will also increase the stormwater
detention capacity of the Tukwila Pond.
Performance Standards
Hydrology Performance Standards
The design performance standards used to assess wetland hydrology include:
• Open water wetland — water from 0 to more than 7ft deep November through
May;
• Emergent wetland — saturated soil between 17.2 and 17.7ft elevation November
through June (the hydrology performance standard for the existing degraded
wetland [now folded into the emergent wetland] ranged from 17.7 to 20.0ft);
• Scrub -shrub wetland — saturated soil between 17.7 and 18.2ft elevation
November through May; and
• Forested wetland — saturated soil between 18.2 and 19.2ft elevation November
through April.
Vegetation Performance Standards
The vegetation performance standards include:
• Emergent wetland — at least 3 or more native emergent plant species each
consisting of at least 20% of total native emergent plant cover and ranging from 1
to 4 ft tall at the end of the 1-year monitoring effort;
• Scrub -shrub wetland — at least 2 or more native shrub plant species each
consisting of at least 20% of total native shrub plant cover and ranging from 4 to
8 ft tall at the end of the 1-year monitoring effort;
• Forested wetland — at least 2 or more native tree plant species each consisting of
at least 20% of total native tree plant cover and ranging from 8 to 20ft tall at the
end of the 1-year monitoring effort;
• The total native plant cover for each wetland class in Year 3 will be at least:
• Emergent — 30%,
• Scrub -Shrub — 30%,
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Third Annual Wetland Mitigation Monitoring Tukwila Pond Mitigation Site
Tukwila, Washington
• Forested — 15%, and
• No more than 20% of the vegetation will consist of non-native invasive plant
species at any time during the monitoring period.
MITIGATION AREA OBSERVATIONS
The 2009/2010 water year was wetter than normal. Excess precipitation for the 6 'wet'
months ranged from 21 % to 73% of normal. The two 'dry' months — November and
February — were 51 % and 16% drier than normal. A normal amount of precipitation fell
in March (Table 1).
Much of the wetland was flooded for a significant period. The open water channel was
flooded a month longer than it was in 2009. Water was somewhat more than a foot
deep in mid -August (Table 2). Parts of the emergent, scrub -shrub, and forested wetland
classes were flooded though the end of June. Other areas were flooded though May.
Wetland hydrology was consistently present through the target date for the existing
forested and open water wetlands. Depending on the elevation of the ground, wetland
hydrology was either present or absent through the target date in parts of the scrub -
shrub and emergent wetlands.
The total cover of installed, volunteer and non-native plant species ranged from 3 to
197% (Table 3). As expected plant cover in the open water wetland was negligible,
although in some areas grasses and herbs adapted to prolonged flooding in shallow
water are colonizing the channel. About half of the plant cover in the emergent wetland
is represented by tree seedlings. Similarly, nearly half the cover in the scrub -shrub
wetland is represented by tree seedlings. Willow is aggressively colonizing that part of
the mitigation area that is regularly flooded. Trees represent nearly half of the cover in
the forested wetland. As expected, trees represent most of the cover in the existing
forest. Table 4 shows the vegetative results relative to the performance standards. To
date Wig has met all but two of the vegetative standards. Only one dominant is present
in the emergent wetland (three are required) and the average height of the vegetation on
the forested wetland is less than the 20ft requirement.
The following paragraphs summarize our observations based on the data collected in
2010 by wetland class.
Emergent Wetland
Based on the 2010 hydrology data for the emergent wetland it would appear that
wetland hydrology met the performance target in three of the four wells (Table 2). Two
of the areas as represented by wells G-103 & G-7 were flooded through the end of June.
The groundwater in the area represented by well G-106 was below or at the target
elevation through the end of June; however, we never observe surface soil saturation at
this location. Well G-101 missed the target significantly. Here groundwater ranged
from 1.1 to 1.5ft below the target elevation from the end of March through the end of
June. The area represented by well G-101 does not meet the regulatory wetland
hydrology requirement of being inundated or saturated to the surface for more than 30
consecutive days.
The emergent wetland in the northeast corner of the site is dominated by herbs and tree
seedlings, including tufted hairgrass, creeping buttercup, and black cottonwood. Other
5 08/13/10
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Third Annual Wetland Mitigation Monitoring
Tukwila, Washington
Tukwila Pond Mitigation Site
common plant species include bulrush, soft rush, and Pacific willow (Attachment A —
Photograph 1). The emergent wetland in the southwest corner of the site is dominated
by creeping buttercup, black cottonwood, and Pacific willow. Soft rush and western
yellowcress are common (Photograph 2). Branches of willow trees have fallen into the
emergent wetland from the adjacent willow forest at a number of spots. The black
cottonwood and willow seedling that form a virtual carpet in areas of prolonged flooding
suggest that these parts of the emergent wetland will eventually become forested
wetland.
There are a total of 25 different plant species in the emergent wetland. The native plant
species cover 96% of the emergent wetland; far more than the 30% Year 3 cover
standard (Table 4). The dominant plant species — black cottonwood and Pacific willow
seedlings — represent more than half of the total vegetative cover. Less than 1 % of the
cover is attributable to non-native invasive plant species (Table 3).
Scrub -Shrub Wetland
Two of the three wells in the scrub -shrub wetland met the hydrology performance target
(Table 2). One area was flooded through the end of June; the other area was flooded
through the beginning of June. From a regulatory perspective the areas represented by
all three wells exhibited wetland hydrology because the soil was saturated to the surface
for at least 30 consecutive days during the growing season. From the performance
standard perspective the area in the vicinity of well G-105 missed the hydrology target.
We counted a total of 17 plant species in the scrub -shrub wetland (Table 3). The total
native plant cover (110%) far exceeds the 30% Year 3 cover standard (Table 4). The
areas that are regularly flooded (G-8 & G-109) are dominated by Sitka willow saplings,
Pacific willow seedlings, and soft rush. Black cottonwood saplings and spotted
ladysthumb are common (Photographs 3 & 4). The non -flooded shrub -shrub wetland is
dominated by red -osier dogwood and tufted hairgrass. Hooker willow saplings are
common (Photograph 5). We observed only a trace of non-native invasive plants in this
wetland class.
Forested Wetland
Both of the wells in the forested wetland met the hydrology performance target (Table 2).
They also met the regulatory hydrology requirement.
The forested wetland is covered with a thick blanket of vegetation (Photograph 6). We
counted 14 different plant species (Table 3). The 102% cover of native plants far
exceeds the 15% Year 3 cover standard (Table 4). Pacific willow, red -osier dogwood,
American sloughgrass, tufted hairgrass, and creeping buttercup dominate. Climbing
nightshade is common in the forested wetland. We observed only a trace of non-native
invasive plants in this wetland class.
In late April we observe that several of the installed trees appear to be dying. On closer
inspection we saw that several black cottonwood and red alder trees are rooted in
standing water during the early growing season. Both of these tree species are adapted
to mesic (i.e., moderate) water regimes, but not hydric (i.e., flooded are prolonged
surface soil saturation) water regimes. In August we counted 11 dead red alder trees
and 9 black cottonwood trees. It is entirely possible that additional red alder trees will
expire in the next year or so due to prolonged flooding during the early growing season.
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Third Annual Wetland Mitigation Monitoring
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Tukwila Pond Mitigation Site
Although the outer bark of the Oregon ash trees has been gnawed by small rodents,
none of these threes are dead. They are adapted to wetter soil conditions than are the
alder and cottonwood.
Open Water Wetland
The hydrology performance standard for the open water wetland was achieved in 2010.
This wetland class was flooded through the middle of August with nearly 1.5ft of water
(Table 2).
Near the end of the second growing season the open water wetland continues to be
sparsely vegetated. The presence of standing water limits the vegetation in this wetland
class. We observed 2 different plant species that cover 3% of the area (Table 3).
Although not rooted in the open water wetland willow branches overhang the channel in
places (Photograph 7). In other places aquatic vegetation is beginning to colonize the
more protected areas (Photograph 8). We observed no non-native invasive plant
species in the open water wetland.
Existing Forested Wetland
Wetland hydrology for the existing forested wetland was present through the end of June
(Table 2).
Three of our original wells are located in existing forested areas dominated by Pacific
willow trees ranging from 45 to 50ft tall. The total vegetative cover for the existing
forested wetland is 197%, with trees representing 130%, shrubs 3%, and herbs 33% of
the cover, respectively (Table 3). In addition to Pacific willow, dominant plant species
include Sitka willow, creeping buttercup, and Watson willow -herb. Grasses are common
volunteers. We observed only a trace of non-native invasive plants in this wetland class.
CONCLUSIONS
The wetland mitigation plan for the Tukwila Pond site currently appears to be on track.
Hydrology
With a few possible exceptions it appears that wetland hydrology in the created and
enhanced wetlands is present. After three years of monitoring it appears that one area —
the area represented by well G-101 — may not meet the hydrology performance
standard. This area has consistently been 'dry' since the wetland was
created/enhanced. A hydrological snapshot of this area in early April 2005 and mid -April
2006 prior to creation/enhancement indicates that this area functioned as upland prior to
grading. At that time depth to groundwater ranged from 2.3 to 4.1ft below the ground
surface.
Other areas not a part of the open water wetland is wetter than planned. These areas
are subject to prolonged seasonal flooding and are represented by wells G-103 & G-7
(emergent wetland), G-8 & G-109 (scrub -shrub wetland), and G-113 (forested wetland).
All of these areas are adjacent to the open water wetland and are in the process of being
dominated by Pacific willow.
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Third Annual Wetland Mitigation Monitoring
Tukwila, Washington
Tukwila Pond Mitigation Site
Vegetation
Wig is on track to meet the vegetative performance standards. Many of the cover and
height requirements have been met (Table 4). Although the data does not show it, we
observe considerably more non-native invasives on the site, particularly reed
canarygrass and purple loosestrife. What were once small clumps are now small
patches of reed canarygrass. Purple loosestrife has spread beyond the western edge of
the Pacific willow forest. It is now also present along the edge of the open water wetland
in the northeastern sector of the wetland.
LIMITATIONS
Work for this project was performed, and this letter report prepared, in accordance with
generally accepted professional practices for the nature and conditions of the work
completed in the same or similar localities, at the time the work was performed. It is
intended for the exclusive use of Wig Properties LLC-SS and their assigns for specific
application to the referenced property. This report is not meant to represent a legal
opinion. No other warranty, express or implied, is made.
Any questions regarding our work and this report, the presentation of the information,
and the interpretation of the data are welcome and should be referred to the
undersigned.
Sincerely,
Chad Armour, LLC
Chad Armour
Principal
Table 1 — Precipitation measured at SeaTac from October 2009 through June 2010
Table 2 — Third Year (2010) subsurface hydrologic characteristics on the mitigation site
Table 3 — Third Year (2010) vegetation characteristics on the mitigation site
Table 4 — Third Year (2010) performance standard assessment for the mitigation site
Figure 1 — Vicinity Map
Figure 2 — Post -Construction Plan
Attachment A — Representative Photographs
cc: Sandra Whiting, City of Tukwila
Amy Klein, U.S. Army Corps of Engineers
Patrick McGraner, Department of Ecology
C:/Jobs/Wig/3rd Year Mitigation Report.doc 8 08/13/10
Chad Armour, LLC
68
TABLES
69
Third Annual Wetland Mitigation Monitoring
Tukwila, Washington
Tukwila Pond Mitigation Site
Table 1 - Precipitation measure at SeaTac from October 2008 through June 2009
Month
October
November
December
January
February
March
April
Measured Normal
5.54 3.19
8.96
2.75
6.17
3.52
5.9
5.62
5.13
4.18
1.04
-0.66
3.76 3.75 0.01
Cumulative Departure
2.35
5.41
2.54
3.58
2.92
2.93
May
June
3.49 2.
59 0.90
2.83 1.78
........
1.05
2.49 1.49 1.00
3.83
4.88
5.88
C:/Jobs/Wig/3rd Year Mitigation Report .doc 08/12/10
Chad Armour, LLC
70
Tukwila Pond Mitigation Site
Groundwater Elevation ft)a
3/31/10 4/27/10 6/1 /10 6/30/10 8/11/210
18.88f 18.75f 118.559 18.44g I 16.6
18.83f I 18.68f 1 18.519 18.42g 17.2
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G-4b Forested Wetland (ex) 18.5
G-11 b Forested Wetland (ex) 13.5
G-7 Emergent Wetland 17.6
G-101 Emergent Wetland 19.4
G-103 Emergent Wetland 18.0
G-106 Emergent Wetland 19.2
G-8 Scrub -Shrub Wetland 18.5
1 G-105 Scrub -Shrub Wetland 18.9
G-109 Scrub -Shrub Wetland 17.8
G-113 Forested Wetland 18.0
fi G-115 Forested Wetland 18.9
G-10 Open Water Wetland 15.0
G-12 Open Water Wetland 15.0
G-14 Open Water Wetland 15.0
S-1 Open Water Wetland 15.1
S-2h Open Water Wetland 18.7
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racemosa --
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Native Shrub Subtotal 0% --
Rubus discolor 1 -- 1 --
Non-Native Invasive Shrub Subtotal 0%
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on Report .doc
72
Tukwila Pond Mitigation Site
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common cattail T pha latifolia -- --
Ranunculus
creeping buttercup . repens --
unidentified grasses --
Geum
large -leaved evens n macrophyllum -
mint Mentha sp. -- --
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prostrate knotweed aviculare 3% 33%
slough sedge Carex obnupta -- I --
soft rush I Juncus effusus --
spatter-dock I Nuphar lutem--
Polygonum
spotted ladysthumb = persicaria -- --
` Carex
thick-headed sedge � pachystachya_I --
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three -square bulrush americana -- T
Deschampsia
tufted hairgrass cespitosa -- I --
Epilobium
willowherb watsonii -- --
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western yellowcress curvisiliqua , --
1
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73
Tukwila Pond Mitigation Site
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Non -Native Invasive Herbs Subtotal
Total Herbs
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74
Third Annual Wetland Mitigation Monitoring
Tukwila, Washington
Tukwila Pond Mitigation Site
Table 4 - Third Year (2010) performance standard assessment for the Tukwila
Pond mitigation site
Performance
Standard
Cover of native
dominantsa
Dominant
Plant S•ecies
Pacific willow
Plant Association
Emer•ent 1 Scrub -Shrub
Forested
52%0
--
37% 16%
4% 28%
Sitka willow
red-osier dogwood
T 10%
20%
tufted hairgrass
16% 33%
10%
Total native plant
coverb
96% 110%
102%
Non-native invasive
coverc
T T
T
Average plant
heights
3.6ft 6.1ft
4.6ft
a Year 10 standard - 20% cover for 3 species (Emergent) & 20% cover for 2 species
(Scrub -shrub & Forested)
b Year 3 standard - Emergent 30%, Scrub -shrub 30%, Forested 15%
° Standard <20%
s 1-4 ft (EM) Year 3 Standard, 4-8 ft (SS) Year 5 Standard, & 8-20 ft (FO) Year 7 Standard
shaded species are dominants
C:/Jobs/Wig/3`d Year Mitigation Report .doc 08/12/10
Chad Armour, LLC
75
FIGURES
76
.1r
Source: The Thomas Guide, 2002, King/Pierce/Snohomish Counties; Page 655.
Tukwila Pond Site]
NOT TO SCALE
FIGURE 1: VICINITY MAP
Wig Properties LLC-SS
Tukwila, Washington
Chad Armour, LLC
6500 126' Avenue SE
Bellevue, Washington 98006
77
78
ATTACHMENT A
Representative Photographs
79
Third Annual Wetland Mitigation Monitoring
Tukwila, Washington
00,10',N!?kolor
Tukwila Pond Mitigation Site
Photograph 1. View of the Emergent Wetland from Plot G-101 looking southeast.
��mipmV�Il�lilY�
IPIIP,1„„,,,
Photograph 2. View of the Emergent Wetland from Plot G-7 looking east.
C:/Jobs/Wig/3rd Year Mitigation Report .doc
Chad Armour, LLC
08/13/10
80
Third Annual Wetland Mitigation Monitoring
Tukwila, Washington
Tukwila Pond Mitigation Site
Photograph 3. View of the Scrub -Shrub Wetland from Plot G-109 looking west.
dlii1flllY11
h ° I'IIIN „
u
Photograph 4. View of the Scrub -Shrub Wetland from Plot G-8 looking east.
C:/Jobs/Wig/3rd Year Mitigation Report .doc
Chad Armour, LLC
08/13/10
81
Third Annual Wetland Mitigation Monitoring
Tukwila, Washington
Tukwila Pond Mitigation Site
Photograph 5. View of the Scrub -Shrub Wetland from Plot G-115 looking northeast.
IPAV
Photograph 6. View of the Forested Wetland from Plot G-105 looking southwest.
C:/Jobs/Wig/3rd Year Mitigation Report .doc 08/13/10
Chad Armour, LLC
82
Third Annual Wetland Mitigation Monitoring
Tukwila, Washington
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gel
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1111111111111111111101111111111
Tukwila Pond Mitigation Site
III III
111111111111111111111111111
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Photograph 7. View of the Open Water Wetland from Plot G-10 looking west.
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11) Illlllllu ppuu �BdVI'^mI�klm ulll u������m��Mw�.
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Photograph 8. View of the Open Water Wetland from Plot G-12 looking southwest.
C:/Jobs/Wig/3rd Year Mitigation Report .doc
Chad Armour, LLC
08/13/10
83
Third Annual Wetland Mitigation Monitoring
Tukwila, Washington
Tukwila Pond Mitigation Site
Photograph 10. View of the Existing Forested Wetland from Plot G-2 looking southwest.
Photograph 10. View of the Existing Forested Wetland from Plot G-4 looking northwest.
C:/Jobs/Wig/3rd Year Mitigation Report .doc 08/13/10
Chad Armour, LLC
84
Source: The Thomas Guide, 2002, King/Pierce/Snohomish Counties; Page 655.
ukwila Pond Sit
NOT TO SCALE
FIGURE 1: VICINITY MAP
Wig Properties LLC-SS
Tukwila, Washington
Chad Armour, LLC
6500 126'" Avenue SE
Bellevue, Washington 98006
85
Wetland E
(179 sf)
Wetland A
(13,718 sf)
•5P-1 P-120
24 ..,
23
MINKLER BOULEVARD
O P-1 Monitoring Well Designation and Location
• SP-1 Plot ID Designation and Approximate Location
Photograph Number and Direction
Survey Source: Bush, Roed & Hitchings, Inc.
0
80 160
Scale in Feet
FIGURE 2: SITE PLAN (REVISED)
Wig Properties
Tukwila, Washington
Chad Armour, LLC
6500 126th Avenue SE
Bellevue, Washington 98006
DATE:
DWG NAME:
86
07/06/0
rrnour\Wig Properties\wig002.dwg
CO
00
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Tukwila
Wetlands
1110 1,000 square
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1,001-4,000
square feet
4,000 square
feet or larger
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TITLE 18 — ZONING
Sections:
18.70.010
18.70.020
18.70.030
18.70.040
18.70.050
18.70.060
18.70.070
18.70.080
18.70.090
18.70.100
18.70.110
18.70.120
18.70.130
CHAP f��� 00000IOR 1 870
NO ,C 14IIII OIIklVlIIIIit G ILOTS,
sT'f"RUC°T"UURES A i`IIII) usIllr''`;$
Purpose
Construction Approved Prior to Adoption of Title
Substandard Lots
Nonconforming Uses
Nonconforming Structures
Repairs and Maintenance
Building Safety
Nonconforming Parking Lots
Nonconforming Landscape Areas
Conditional and Unclassified Uses
Nonconforming Adult Entertainment Establishment
Sidewalk Dedication
Cargo Containers
18.70.010 Purpose
It is the purpose of this chapter to establish limitations on the
expansion and extension of nonconforming uses and structures
which adversely affect the development and perpetuation of
desirable residential, commercial, and industrial areas with
appropriate groupings of compatible and related uses.
(Or 1819 §1 (tram), 1997)
18.70.020 Construction Approved Prior to Adoption of
Title
To avoid undue hardship, nothing in this title shall be deemed
to require a change in plans, construction or designated use of any
building on which actual construction was lawfully begun prior to
adoption of this title and upon which actual building construction
has been carried on in a diligent manner. Actual construction shall
consist of materials in permanent positions and fastened in a
permanent manner, and demolition, elimination and removal of
one or more existing structures in connection with such
construction; providing, that actual construction work shall be
diligently carried on until the completion of the structure involved.
(Ord 1819 §1 (a 1, 1 1(
18.70.030 Sustandard Lots
A. A lot, as defined in TMC 18.06.500, which does not meet
the minimum standard for average lot width for the zone in which
it is located, may still be developed as a separate lot if the
proposed use is one which is permitted in the zone, and the
proposed development can comply with the remaining
requirements of this title regarding basic development standards
for the applicable zone and other applicable land use and
environmental requirements.
B. A lot, as defined in TMC 18.06.500, which cannot meet
the basic development standards (other than lot width) for the
applicable zone and other applicable land use and environmental
requirements, may be developed only if it is combined with
adjacent lot(s) in a manner which allows the combined lots to be
developed in a manner which does comply with the basic
development standards for the applicable zone and other
applicable land use and environmental requirements. In the event
lots are combined in order to comply with the requirements of this
subsection, a boundary line adjustment shall occur so that the
combined lots are henceforth considered a single lot.
C. Nothing in this subsection shall be deemed to prevent the
owner of a sub -standard lot from applying for or receiving approval
of variances pursuant to TMC Chapter 18.72.
18.'70.040 NonconformingUses
Any preexisting lawful use of land made nonconforming under
the terms of this title may be continued as a nonconforming use,
defined in TMC Chapter 18.06, so long as that use remains lawful,
subject to the following:
1. No such nonconforming use shall be enlarged,
intensified, increased or extended to occupy a greater use of the
land, structure or combination of the two, than was occupied at the
effective date of adoption of this title.
2. No nonconforming use shall be moved or extended
in whole or in part to any other portion of the lot or parcel occupied
by such use at the effective date of adoption or amendment of this
title.
3. If any such nonconforming use ceases for any
reason for a period of more than six consecutive months, or a total
of 365 days in a three-year time period, whichever occurs first, any
subsequent use shall conform to the regulations specified by this
title for the district in which such use is located.
4. No existing structure devoted to a use not permitted
by this title in the zone in which it is located shall be structurally
altered, except in changing the use of the structure to a use
permitted in the zone in which it is located; except where minor
alterations are made, pursuant to TMC Section 18.70.050(1), TMC
Section 18.70.060, or any other pertinent section, herein.
5. If a change of use is proposed to a use determined
to be nonconforming by application of provisions in this title, the
proposed new use must be a permitted use in its zone or a use
approved under a Conditional Use or Unclassified Use Permit
process, subject to review and approval by the Hearing Examiner
and/or the City Council. For purposes of implementing this
section, a change of use constitutes a change from one Permitted,
Conditional or Unclassified Use category to another such use
category as listed within the Zoning Code.
6. Any structure, or structure and land in combination,
in or on which a nonconforming use is superseded by a permitted
use, shall thereafter conform to the regulations for the zone in
which such structure is located, and the nonconforming use may
not thereafter be resumed.
(Ord 111100 § 1,2016; Ord 1819 §1(1(, 111111(
Produced by the City of Tukwila, City Clerk's Office
Page 18-209
91
TUKWILA MUNICIPAL CODE
18.70.050 Nonconforming Structures
Where a lawful structure exists at the effective date of
adoption of this title that could not be built under the terms of this
title by reason of restrictions on area, development area, height,
yards or other characteristics of the structure, it may be continued
so long as the structure remains otherwise lawful subject to the
following provisions:
1. No such structure may be enlarged or altered in such
a way that increases its degree of nonconformity. Ordinary
maintenance of a nonconforming structure is permitted, pursuant
to TMC Section 18.70.060, including but not limited to painting,
roof repair and replacement, plumbing, wiring, mechanical
equipment repair/replacement and weatherization. These and
other alterations, additions or enlargements may be allowed as
long as the work done does not extend further into any required
yard or violate any other portion of this title. Complete plans shall
be required of all work contemplated under this section.
2. Should such structure be destroyed by any means to
an extent of more than 50% of its replacement cost at time of
destruction, in the judgment of the City's Building Official, it shall
not be reconstructed except in conformity with provisions of this
title, except that in the LDR zone, structures that are
nonconforming in regard to yard setbacks or sensitive area
buffers, but were in conformance at the time of construction may
be reconstructed to their original dimensions and location on the
lot.
3. Should such structure be moved for any reason or
any distance whatsoever, it shall thereafter conform to the
regulations for the zone in which it is located after it is moved.
4. When a nonconforming structure, or structure and
premises in combination, is vacated or abandoned for 24
consecutive months, the structure, or structure and premises in
combination, shall thereafter be required to be in conformance
with the regulations of the zone in which it is located. Upon
request of the owner, the City Council may grant an extension of
time beyond the 24 consecutive months.
5. Residential structures and uses located in any
single-family or multiple -family residential zoning district and in
existence at the time of adoption of this title shall not be deemed
nonconforming in terms of bulk, use, or density provisions of this
title. Such buildings may be rebuilt after a fire or other natural
disaster to their original dimensions and bulk, but may not be
changed except as provided in the non -conforming uses section
of this chapter.
6. Single-family structures in single- or multiple -family
residential zone districts that have legally nonconforming building
setbacks, shall be allowed to expand the ground floor only along
the existing building line(s), so long as the existing distance from
the nearest point of the structure to the property line is not
reduced, and the square footage of new intrusion into the setback
does not exceed 50% of the square footage of the current
intrusion.
7. In wetlands, watercourses and their buffers, existing
structures that do not meet the requirements of the Sensitive
Areas Overlay District chapter of this title may be remodeled,
reconstructed or replaced, provided that:
a. The new construction does not further intrude
into or adversely impact an undeveloped sensitive area or the
required buffer;
b. The new construction does not threaten the
public health, safety or welfare; and
c. The structure otherwise meets the requirements
of this chapter.
8. In areas of potential geologic instability, coal mine
hazard areas, and buffers, as defined in the Sensitive Areas
Overlay District chapter of this title, existing structures may be
remodeled, reconstructed or replaced, provided that:
a. The new construction is subject to the
geotechnical report requirements and standards of TMC Sections
18.45.120B and 18.45.120C;
b. The new construction does not threaten the
public health, safety or welfare;
c. The new construction does not increase the
potential for soil erosion or result in unacceptable risk or damage
to existing or potential development or to neighboring properties;
and
d. The structure otherwise meets the requirements
of this chapter.
9. A nonconforming use, within a nonconforming
structure, shall not be allowed to expand into any other portion of
the nonconforming structure.
(Ord, 2518 §15, 2016; Ord, 2175 1, 2007; Ord, 2077 §1, 2004;
Ord, 1819 "t (part), 1997)
18.70.060 Repairs and Maintenance
If any building is devoted in whole or in part to any
nonconforming use, work may be done in any period of twelve
consecutive months on ordinary repairs, or on repair or
replacement of nonbearing walls, fixtures, wiring or plumbing to an
extent not exceeding 25% of the current replacement value of the
building.
(Ord. 1819 §1 (part), 1997)
18.70.070 Building Safety
A. Nothing in this title shall be deemed to prevent the
strengthening or restoring to a safe condition of any
nonconforming building or part thereof declared to be unsafe by
order of any City official charged with protecting the public safety.
B. Alterations or expansion of a nonconforming use which
are required by law or a public agency in order to comply with
public health or safety regulations are the only alterations or
expansions allowed.
(Ord. 1819 §1(mart), 1997)
18.70.080 Nonconforming Parking Lots
A. Nothing contained in the Off-street Parking and Loading
Regulations chapter of this title shall be construed to require a
change in any aspect of a structure or facility covered thereunder
including, without limitation, parking lot layout, loading space
Page 18-210
92
Produced by the City of Tukwila, City Clerk's Office
AV'V'1G"CVvu4NV'4
Alterations allowed
according to code: Lateral expansion
Redmond
Bellevue
Issaquah
SEATAC
Kent
Des Moines
Tukwila
Renton
Kirkland
Non -conforming regulations for critical areas
Vertical expansion Repairs/Maintenence
May be enlarged or
expanded if the level of
conformity isn't
increased, and the impact Nothing mentioned
to the critical area isn't
increased.
Prohibited if it further
encroaches on the critical Nothing mentioned
area
Allowed if conformity
and proximity to critical
area isn't altered.
Minor, nonstructural,
and repairs of
mechanical systems
within or supporting the
accessory structure
allowed
Building expansion over
existing impervious
surface area within the
buffer is allowed provided Existing buildings may
expand vertically to Nothing mentioned
the building expansion
does not encroach closer add upper stories.
toward a wetland or
stream.
Nothing mentioned
Nothing mentioned
Repair and
maintenance of non-
conforming uses or
structures is permitted
provided they do not
increase the degree of
nonconformity
Reconstruction
Allowed if 50% or more
of its value has been
destroyed. Can't
increase footprint or
harm critical area
further.
If destroyed by an
unforseen circumstance,
the structure can be
rebuilt in the same
footprint, if commenced
within one year of
destruction. Temporary
distrubance of
surrounding areas from
this construction will be
restored afterwards.
Incentives.
Groundwater
protection
incentive program:
level of
nonconformity
may be increased if
this mitigates the
potential
stormwater
impacts to
groundwater.
Nothing mentioned
If destroyed by an
unforseen circumstance,
the structure can be Nothing mentioned
rebuilt in the same
footprint.
Nothing mentioned
Reconstruction or additions to existing structures that intrude into critical areas or their buffers shall
not increase the amount of such intrusion
Nothing mentioned
Where a legally established, nonconforming use of the buffer exists (e.g., a road or structure that
lies within the width of buffer recommended for that wetland), proposed actions in the buffer may
be permitted as long as they do not increase the degree of nonconformity, or if no reasonable
alternative exists. This means no increase in the impacts to the wetland from activities in the buffer. Nothing mentioned
Allowed if the
Allowed if it doesn't reconstruction doesn't
Nothing mentioned Nothing mentioned affect the critical area intrude further into or
or buffer impact the sensitive area
or buffer
Only permitted if it doesn't infringe further into
the critical area or increases the level of Nothing mentioned
nonconformity
If it doesn't increase the
level of nonconformity,
expansion is allowed if it
doesn't encroach further
into the critical area or
buffer. If it does increase
the level of
nonconformity, very
specific guidelines must
be followed (see code).
Upper floor additions
are allowed above
the ground floor of
an existing
nonconforming
building if they do
not encroach closer
to the critical area
buffer or structure
setback from the
buffer beyond the
existing exterior
walls
Allowed provided that
the work does not
increase the previously
approved structure
footprint or impervious
area.
Can only be
reconstructed if the new
structure or use is in
conformity with the
code, except for ongoing
agricultural use.
Nothing mentioned
Can be reconstructed if
the new construction
doesn't increase the
footprint. Existing buffer Nothing explicitly
fencing, native buffer mentioned
vegetation and
dedication of the critical
area must be retained.
93
94
ATTAC ENT 1'
Kirkland Zoning Code:
90.185 Nonconformances in Critical Areas
6. Expansion of Nonconforming Building that Increases the Nonconformance — An existing,
legally established nonconforming building may be expanded into a critical area buffer or the building
setback under the following standards and limitations:
a. General Standards for Any Expansion
1) Expansion is only permitted for those buildings that have not received City approval for a
critical area or buffer modification allowed under this or a previous code or not received
approval for a reasonable use exception pursuant to KZC 90.180;
2) A one (1) time expansion of each option found in subsections (6)(b) through (e) of this
section is permitted on a subject property. No more than one expansion is permitted for
each option. See vegetative buffer standards in KZC 90.130;
3) No expansion is permitted in a critical area buffer that is a fish and wildlife conservation
area without an approved management plan pursuant to KZC 90.95;
4) The following nonconforming improvements are allowed without going through review
under subsections (6)(b) through (e) of this section if a new or replacement foundation is not
required:
a) Upper floor additions are allowed above the ground floor of an existing
nonconforming building if they do not encroach closer to the critical area buffer or
structure setback from the buffer beyond the existing exterior walls;
b) Existing carports and decks with roofs may be enclosed if the new exterior walls do
not extend beyond the existing foundation or corner supports of the structure; and
c) An interior open courtyard of an existing building may be enclosed if the courtyard
is covered entirely with impervious material. See subsection (6)(d) of this section if the
material is not entirely impervious;
5) Covering an existing deck with a roof or an existing pathway with a breezeway or similar
improvements may be proposed using subsections (6)(b) through (e) of this section;
6) Any commercial parking required for additions shall not be located in the critical area
buffer;
7) A critical area determination, report and a survey pursuant to KZC 90.105 and 90.110 are
required if the wetland has not been rated and delineated pursuant to KZC 90.55 within the
past five (5) years or the stream has not been classified or delineated pursuant to KZC 90.65;
8) Compensatory mitigation through buffer restoration shall be provided as follows:
95
a) A native vegetative buffer at a minimum ratio of 1:1 (new footprint area is equal to
or less than vegetative buffer area) shall be provided;
b) If the new or expanded building footprint results in removal of a significant tree in
a buffer, the tree shall be replaced with two (2) native trees in the buffer. The
replacement tree shall be six (6) feet tall for a conifer and 2-inch caliper for deciduous
or broadleaf. For a removed significant tree in a buffer that is 24 inches in diameter, the
tree shall be replaced with three (3) native trees;
c) The vegetative buffer shall be located along the edge of the critical area or as close
to the critical area as possible if the critical area is located off -site;
d) The vegetative buffer shall be 10 feet in depth and located across from the building
expansion area;
e) The buffer vegetative standards pursuant to KZC 90.130 shall be used as a guideline
for the mitigation area; and
f) The mitigation is in addition to revegetation of any disturbed area;
9) A mitigation planting plan, prepared by a qualified critical area professional approved by
the City, shall be submitted for approval as part of the building permit. Prior to final
inspection, replanting of any disturbed area and the mitigation planting shall be installed by
the applicant and inspected by the City;
10) A performance and three-year maintenance and monitoring security shall be submitted
with the building permit pursuant to KZC 90.165 for the mitigation plan;
11) Permanent critical area fencing and signage is required. Prior to issuance of a building
permit, the Planning Official shall determine the location of the required critical area fencing
and signage to be installed pursuant to KZC 90.190.
a) The fencing shall be located at the edge of the buffer. However, if all or portions of
the buffer is covered by legally established lawn, nonnative vegetation and/or
improvements, then the fencing shall be located at the boundary of that maintained
area;
b) If the critical area is off site and that maintained area extends to the property line,
then the fencing shall be located at the property line; and
c) Existing buffer fencing may need to be relocated to meet this provision;
12) A critical area covenant on a form approved by the City shall be recorded along with an
as -built site plan showing the location of the approved expansion and mitigation vegetation
in the buffer to protect the vegetated portion of the buffer in perpetuity. A critical area
dedication pursuant to KZC 90.210 is not required for the vegetated portion of the buffer.
96
b. Expansion into Critical Area Buffer on Side of the Building Opposite of Critical Area
1) The footprint of an existing building may be expanded into the critical area buffer on the
side of the building opposite of the critical area buffer up to a maximum of 1,000 square
feet. The existing building must be between the addition and the critical area (see Chapter
180 KZC, Plate 26);
2) Only a one (1) time expansion of this option is permitted for the subject property. See
subsection (6)(a)(2) of this section; and
3) See general standards in subsection (6)(a) of this section for an expansion.
c. Expansion into Structure Setback from the Buffer
1) The footprint of an existing building may be expanded into the structure setback up to a
maximum of 500 square feet;
2) If an addition is located at the edge of the buffer, the portion of the buffer next to the
side of the addition abutting the buffer is considered a structure setback from the buffer.
Only necessary maintenance and repair of the addition are permitted in this portion of the
structure setback. No improvements pursuant to KZC 90.140 are permitted in this portion of
the structure setback;
3) Only a one (1) time expansion of this option is permitted for the subject property. See
subsections (6)(a)(2) of this section; and
4) See general standards in subsection (6)(a) of this section for a building expansion.
d. Expansion into Critical Area Buffer but No Closer than the Existing Building
1) The footprint of an existing building may be expanded into the critical area buffer, but
no closer than the edge of the existing building nearest to the critical area, up to a maximum
of 500 square feet (see Chapter 180 KZC, Plate 26);
2) An interior open courtyard of an existing building may be enclosed up to 500 square feet
if the courtyard is covered partially or entirely with pervious material. This improvement can
be done in conjunction with subsection (6)(d)(1) of this section if the total new impervious
area of the expanded building does not exceed 500 square feet;
3) The minimum buffer width for the addition shall be 60 percent of the required buffer
width standard pursuant to KZC 90.55 for wetlands and KZC 90.65 for streams;
4) Only a one (1) time expansion of this option is permitted for the subject property. See
subsections (6)(a)(2) of this section; and
5) See general standards in subsection (6)(a) of this section for a building expansion.
97
e. Expansion into Critical Area Buffer between the Building and the Critical Area
1) The footprint of a building may be expanded into the critical area buffer between the
building and the critical area up to a maximum of 250 square feet (see Chapter 180 KZC,
Plate 26);
2) The new footprint must be attached to the original building and not to any subsequent
footprint addition under subsection (6) of this section;
3) The minimum buffer width for the addition shall be 60 percent of the required buffer
width standard pursuant to KZC 90.55 for wetlands and KZC 90.65 for streams;
4) Only a one (1) time expansion of this option is permitted for the subject property. See
subsection (6)(a)(2) of this section; and
5) See general standards in subsection (6)(a) of this section for a building expansion.
98