HomeMy WebLinkAboutSWP2703170_3Wetland Mitigation Banking Plan
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City of Renton
Parametrix, Inc. February 2002
Wetland Mitigation Banking Plan
Proposed
Prepared for
City of Renton
1055 South Grady Way
Renton, Washington 98055
Prepared by
Parametrix, Inc.
5808 Lake Washington Blvd. NE, Suite 200
Kirkland, Washington 98033
(425) 822-8880
www.parametrix.com
February 2002
Project No. 553-1779-014 (01/01)
TABLE OF •
EXECUTIVESUMMARY
.............................................................................................................................IV
1.
INTRODUCTION...............................................................................................................................1-1
2.
PROJECT DESCRIPTION AND LOCATION...................................................................................2-1
2.1
PROJECT DESCRIPTION..................................................................................................2-1
2.2
SITE DESCRIPTION..........................................................................................................
2-1
2.3
OWNERSHIP......................................................................................................................2-1
2.4
RESPONSIBLE PARTIES..................................................................................................2-1
2.5
RATIONALE FOR CHOICE.............................................................................................. 2-4
3.
EXISTING
CONDITIONS AND FUNCTIONS OF THE MITIGATION BANKING SITES................3-1
3.1
MITIGATION BANK SITE 1.............................................................................................3-1
3.1.1 Wetland Delineation...............................................................................................3-1
3.1.2 Vegetation Communities........................................................................................3-3
3.1.3 Soils, Hazardous Material, and Geotechnical Information.....................................3-3
3.1.4 Hydrology...............................................................................................................3-4
3.1.5 Functional Assessment...........................................................................................3-5
3.1.6 Wetland Rating.......................................................................................................3-6
3.2
MITIGATION BANK SITE 2.............................................................................................3-7
3.2.1 Wetland Delineation...............................................................................................3-7
3.2.2 Vegetation...............................................................................................................3-7
3.2.3 Soils, Hazardous Material, and Geotechnical Information .....................................
3-7
3.2.4 Hydrology...............................................................................................................
3-9
3.2.5 Functional Assessment...........................................................................................3-9
3.2.6 Wetland Rating.....................................................................................................3-11
4.
MITIGATION APPROACH...............................................................................................................4-1
4.1
MITIGATION SEQUENCING...........................................................................................4-1
4.2
MITIGATION PLAN GOALS, OBJECTIVES, AND PERFORMANCE
STANDARDS......................................................................................................................4-1
4.2.1 Mitigation Banking Site 1.......................................................................................4-1
4.2.2 Mitigation Banking Site 2.......................................................................................4-2
4.3
PERFORMANCE STANDARDS.......................................................................................4-3
4.3.1 Mitigation Banking Site 1.......................................................................................4-3
4.3.2 Mitigation Banking Site 2.......................................................................................4-4
5.
PRELIMINARY SITE DESIGN..........................................................................................................5-1
5.1
TOPOGRAPHY...................................................................................................................5-1
5.2
SOURCE OF WATER........................................................................................................5-1
5.3
SOILS..................................................................................................................................5-1
5.4
PROPOSED PLANT DISTRIBUTION..............................................................................5-5
5.5
SECTION DRAWINGS......................................................................................................5-6
City of Renton 553-1779-014 (01/01)
Wetland Mitigation Banking Plan i February 2002
Mitigation Banking Plan.doc
TABLE OF CONTENTS (Continued)
5.6 PUBLIC ACCESS...............................................................................................................5-6
6.
MONITORING PLAN........................................................................................................................6-1
6.1
VEGETATION ............. ........ ...............................................................................................
6-1
6.2
WATER REGIME ...............................................................................................................6-1
6.3
SOILS..................................................................................................................................6-1
6.4
FAUNA................................................................................................................................6-2
6.5
DEVELOPMENT OF HABITAT STRUCTURE...............................................................6-2
6.6
BUFFERS............................................................................................................................6-2
6.7
SCHEDULE OF REPORTING MONITORING RESULTS..............................................6-2
7.
SITE PROTECTION..........................................................................................................................7-1
7.1
LEGAL PROTECTION.......................................................................................................7-1
7.2
MAINTENANCE AND CONTINGENCY PLAN.............................................................7-1
8.
IMPLEMENTATION..........................................................................................................................8-1
8.1
BACKGROUND.................................................................................................................8-1
8.2
THE CERTIFICATION PROCESS....................................................................................8-1
8.2.1 Prospectus...............................................................................................................8-1
8.2.2 Bank Instrument......................................................................................................8-1
8.3
ECOLOGY REVIEW AND DECISION/PUBLIC NOTIFICATION................................8-3
8.4
ENVIRONMENTAL REVIEW/PERMITS........................................................................8-3
8.5
COST/FUNDING................................................................................................................
8-3
9.
PERFORMANCE..............................................................................................................................9-1
10.
REFERENCES
................................................................................................................................10-1
GLOSSARY
LIST OF FIGURES
1
Location of Mitigation Banking Sites 1 and 2.....................................................................1-2
2
Existing Conditions on Mitigation Banking Site 1..............................................................2-2
3
Existing Conditions on Mitigation Banking Site 2..............................................................2-3
4
Soil Characteristics on Mitigation Banking Site 1...............................................................3-1
5
Soil Characteristics on Mitigation Banking Site 2...............................................................3-2
6a
Preliminary Grading and Landscape Plan for Mitigation Bank Site 1.................................5-2
6b
Preliminary Grading and Landscape Plan for Mitigation Bank Site 1 (Continued) ............5-3
7
Preliminary Grading and Landscape Plan for Mitigation Bank Site 2.................................5-4
8
Implementation Schedule Mitigation Bank Site 1 and 2.....................................................8-2
City of Renton 553-1779-014 (01/01)
Wetland Mitigation Banking Plan ii February 2002
Mitigation Banking Plan. doc
TABLE OF CONTENTS (Continued)
LIST OF TABLES
Table 1. Summary of Functional Evaluation of Wetlands on Mitigation
BankingSite 1..................................................................................................................3-5
Table 2. Summary of Wetland Functions Provided by Mitigation Banking Site 2........................3-9
Table 3. Candidate Plant Species Proposed for Wetlands and Buffers..........................................5-5
Table 4. Proposed Schedule for Monitoring City of Renton Mitigation Banking Sites ................6-3
APPENDICES (Under Separate Cover)
A CITY OF RENTON WETLAND MANAGEMENT ORDINANCE
B SAMPLE WETLAND FUNCTIONAL EVALUATION FORM
C PHOTOGRAPHS OF SOIL CONDITIONS ON MITIGATION BANKING SITE 2
D WETLAND FUNCTION EVALUATIONS FOR MITIGATION BANKING
SITES 1 AND 2
E GLACIER PARK MITIGATION BANK AGREEMENT
F WETLAND DELINEATION REPORTS FOR MITIGATION BANKING
SITES 1 AND 2
G U.S. ARMY CORPS OF ENGINEERS CORRESPONDENCE
H SOILS REPORT
I MONITORING WELL INSTALLATION
J CAPACITY ANALYSIS
K CREST GAUGE AND MONITORING WELL DATA —
MITIGATION BANKING SITE 1
L PRELIMINARY COST ESTIMATES FOR MITIGATION BANKING SITES 1 AND 2
M HYDROLOGIC ANALYSIS FOR MITIGATION BANKING SITE 2
City of Renton 553-1779-014 (01/01)
Wetland Mitigation Banking Plan iii February 2002
Mitigation Banking Plandoc
EXECUTIVE SUMMARY
This Mitigation Banking Plan describes the construction and planning of two wetland ecosystem sites as
part of a City of Renton mitigation banking program. The Mitigation Banking Plan is a method by which
high function wetlands are created contiguous with other significant habitat in the Black River Drainage
Basin to offset the loss of isolated, lower function wetlands that may occur through private and public
development. The mitigation banking program and plan are consistent with the City's Critical Area
Ordinance and Comprehensive Plan. The banking plan provides an approach that preserves or enhances
wetland and ecosystem functions while allowing economic growth in compliance with the state of
Washington's Growth Management Act.
This report provides a conceptual design approach for establishing wetlands and wetland banking credit
on two parcels as part of the City's planned mitigation bank. The plan is conceptual because it remains
subject to several variables such as finalization of wetland banking rules for Washington State, potential
changes to Army Corps of Engineers jurisdiction of isolated wetlands, and review by permitting agencies
for Clean Water Act and Endangered Species Act compliance.
Development of wetlands on two mitigation bank sites are proposed: Mitigation Banking Site 1 (Site 1)
and Mitigation Banking Site 2 (Site 2), which total about 44 acres. Site 1 (about 31 acres) is north of SW
34th Street, south of Boeing Longacres Park, east of Burlington Northern Railroad, and west of Oakesdale
Ave. SW. The site consists of 12 acres of non -wetland and about 19 acres of emergent, shrub, and young
forested wetlands. Site 2 (about 14 acres) is located south of SW 34th Street, west of Springbrook Creek,
north of SW 41" Street and east of Oakesdale Avenue SW. The site consists of about 7 acres of upland
and 7 acres of emergent and shrub wetlands that developed on fill.
The Mitigation Banking Plan provides a preliminary wetland mitigation design for the mitigation banking
sites. A discussion of existing conditions at each mitigation bank site including vegetation, soils, and
hydrology provides baseline information to use to compare with post -project conditions. The existing
conditions assessment indicates that both sites have been impacted by historic and recent clearing, filling, and
grading activities. The existing wetlands are defined as Category 3 wetlands by the City of Renton's
categorization for wetlands.
The mitigation plan's goal for both sites is to establish a total of about 20 acres of wetland that contain four
wetland vegetation classes. Upland buffers would protect these wetlands. The mitigation will enhance
existing wetland functions by providing habitat and food chain support to terrestrial and aquatic wildlife,
habitat connectivity, storm and flood water attenuation, downstream water quality improvements, public
access, and shoreline stabilization. To accomplish this goal, approximately 10 acres of emergent, shrub and
forested wetlands will be established on Site 1 and, for Site 2, approximately 10 acres of open -water,
emergent, shrub, forested wetlands, and transitional buffer. On both sites, the enhancement of existing lower
quality wetland or low quality upland buffers should improve wetland function and generate additional
mitigation credit.
The plan specifies mitigation objectives, performance standards, and the methodology to measure whether
these standards are met. These objectives and standards were developed based on site assessments of wetland
functions and potential mitigation opportunities, including; soils, hydrology, vegetation, habitat, flood and
stormwater attenuation, water quality improvements, public education, and passive recreation.
During a 10-year post -construction monitoring period, the development of the wetland and buffer plant
communities, habitat structure, and other ecological conditions will be measured. Additionally, hydrology,
soils, topography, and vegetation will be monitored to ensure that they are meeting design criteria. The
proposed schedule for monitoring will require preparation of an as -built report after construction and annual
reports that will be submitted to the City of Renton. In addition, if, during the monitoring program,
maintenance needs and/or contingency actions are identified that are required to ensure the success of the
mitigation plan, they will be implemented.
City of Renton 553-1779-014 (01/01)
Wetland Mitigation Banking Plan iv February 2002
Mitigation Banking Plmdac
1. INTRODUCTION
The Mitigation Banking Plan will establish wetland communities at two mitigation banking sites (Figure
1). The mitigation plan includes information generally needed by regulatory agencies to review wetland
mitigation plans. The information contained in this plan generally follows the format provided by
Washington Department of Ecology (Ecology) (1993) for mitigation plans.
This report provides a conceptual design approach for establishing wetlands and wetland banking credit
on two parcels as part of the City's planned mitigation bank. The plan is conceptual because it remains
subject to several variables such as finalization of wetland banking rules for Washington State, potential
changes to Army Corps of Engineers jurisdiction of isolated wetlands, and review by permitting agencies
for Clean Water Act and Endangered Species Act compliance.
The final wetland mitigation plan will provide detailed plans, construction drawings, specifications, and
schedules. The City of Renton (hereafter referred to as the City) and a larger body of technical and
regulatory specialists will review the draft final plan. Input from these specialists will be incorporated
into a final plan thereby increasing the probability of attaining the projects ecological goals.
The Wetland Mitigation Banking Plan will create large, high function, contiguous wetlands adjacent to
Springbrook Creek in the Black River Drainage Basin (see Figure 1). These mitigation wetlands will be
used to offset filling of isolated, low function wetlands that may result from private and public
development in the same drainage basin.
Approximately 10 acres of emergent, shrub, and forested wetlands would be established on the existing
uplands on Mitigation Banking Site 1 (Site 1). Approximately 2.5 acres of existing wetland would be
altered and enhanced by construction of the mitigation. The modification of these existing wetlands is
necessary to establish new wetland communities and provide the desired ecological functions specified
for this site. About 15 acres of existing forest and shrub wetland on the site could be enhanced to
generate additional mitigation credit. The specific functions established by this mitigation are biological
support, floodwater storage, water quality enhancement, wetland education opportunities, and passive
recreation opportunities.
On Mitigation Banking Site 2 (Site 2), approximately 10 acres of open water, emergent wetland, shrub
wetland, forested wetland, and upland buffer'area would be established. To construct Site 2, about 7 acres of
wetland and 7 acres of upland plant communities occurring on fill soils would be modified as the site is
graded to create the desired habitat conditions. The functions to be provided at Site 2 are biological support,
floodwater storage/desynchronization, nutrient and sediment trapping, and shoreline stabilization.
Opportunities for passive recreation and education are also included in the proposed site plan.
S, 33
The City will use about-A41 acres to compensate for permitted filling of wetlands on some Glacier Park
properties. The additional property will be available as mitigation banking credits to offset approved wetland
fill elsewhere.
City of Renton 553-1779-014 (01/01)
Wetland Mitigation Banking Plan 1-1 February 2002
Mitigation Banking Ptan.dot
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SCALE IN FEET Figure 1
Location of Mitigation
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2. PROJECT DESCRIPTION AND LOCATION
2.1 PROJECT DESCRIPTION
The City proposes to develop two wetland mitigation banking sites (called Site 1 and Site 2) totaling 44.80
acres. These sites are to be used for compensatory wetland mitigation for the six parcels originally under
Glacier Park ownership, and for mitigation banking by other public and private developments to offset losses
to lower quality wetlands. Specifically, Site 1 can provide 10 acres of wetland mitigation banking credit. As
proposed, Site 2 will provide 10 acres of wetland mitigation banking. Additional credit may be assigned to
these sites as a result of upland and wetland enhancement actions.
2.2 SITE DESCRIPTION
Site 1 is located north of Southwest 34th Street, south of Boeing's Longacres Park site, east of the Burlington
Northern Railroad, and west of Oakesdale Avenue Southwest (see Figure 1). The site is 30.97 acres and is
partially zoned industrial. It is bordered by developed land zoned for industrial development along most of
the southern boundary. Undeveloped commercial and industrially zoned land is adjacent to the western half
of the southern boundary and to the eastern and western boundaries (David Evans and Associates 1991a).
The site consists primarily of revegetated fill material, placed approximately 20 years ago, consisting of 12.19
acres of upland meadow and shrubland and 18.78 acres of shrub and emergent wetlands (confirmed by the
Army Corps of Engineers in 1996; Appendix G) (Figure 2).
Site 2 is located south of Southwest 34th Street, west of Springbrook Creek, north of Southwest 40 Street,
and east of Oakesdale Avenue Southwest (Sec 25, T 23N, R 4E) (Figure 3). The site is approximately 13.93
acres and consists of 7.24 acres of upland meadow and 6.69 acres of emergent and young shrub and forested
wetland (David Evans and Associates 1991b). The site was filled over the past 20 years; the topography is
relatively flat with small depressional areas. It is bordered by developed industrial land immediately to the
north.
2.3 OWNERSHIP
The City is the sole owner of the two mitigation banking sites. As the City developed its Wetlands
Management Ordinance, Burlington Northern (BN) decided to divest some properties held by the Glacier
Park Company, a subsidiary to BN. BN also wanted to improve the market value of some of its Black River
Valley properties. After meeting with the City to develop a mitigation banking agreement, Glacier Park
donated two large parcels (see Figure 1) that contained wetlands to the City.
2.4 RESPONSIBLE PARTIES
The applicant is the City of Renton, 1055 South Grady Way, Renton, Washington 98055. Contacts at the
City are Mr. Ronald Straka and Mr. Allen Quynn, Department of Public Works, Surface Water Utility.
David Evans and Associates, Inc. delineated the wetlands on the mitigation banking sites, which were
confirmed by the U.S. Army Corps of Engineers in 1996. Parametrix assisted the City with the preparation
of this mitigation banking program and plan.
City of Renton 553-1779-014 (01/01)
Wetland Mitigation Banking Plan 2-1 February 2002
Mitigation Banking Plan.doc
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CITY OF RENTON, 1993
FILE: 177907F2-2DWG
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CITY OF RENTON, 1993 ze
FILE: 177907F8-2.OWG
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[P Parametrix, Inc. — — = Mitigation site boundary Existing Conditions on
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SCALE IN FEET
2.5 RATIONALE FOR CHOICE
Glacier Park donated the mitigation banking sites to the City as part of a mitigation banking agreement
between the City and Glacier Park. The two sites are appropriate as mitigation banking sites for several
reasons. Ecological functions on both sites are degraded by past disturbances that include vegetation
clearing, fill placement, hydrologic modification, and other disturbances. The sites are adjacent to
Springbrook Creek (Site 2) or to other wetlands that are adjacent and hydrologically connected to the creek
(Site 1), and their restoration as wetlands would contribute to function of these systems that provide an
ecological corridor through much of the Renton Valley (see Figure 1). Improvements made to the vegetation
communities and establishing specific wetland functions would result in a net gain in wetland acreage,
habitats, and functions. Both sites have the capability of providing wetland functions that will significantly
benefit the City and the public. For example, the City identified storm and flood water attenuation as an
important issue in the Black River Drainage Basin. Sites 1 and 2 can provide significant floodwater control
that would minimize impacts to downstream areas. In addition, Site 1 is adjacent to protected wetlands to the
north and east. Site 2 immediately borders Springbrook Creek and its associated City -owned wetlands (i.e.,
Panther Creek Wetland).
Both sites have been altered by filling, ditching, or other drainage alterations over the past 20 years, and their
ability to provide functions important to the landscape and Black River Drainage Basin is limited to non-
existent. Wetlands established on these sites could improve the hydrologic and ecological condition of the
Black River Drainage Basin by increasing storm and flood water storage capacity, enhance habitat corridors,
provide biological support functions, and enhance water quality.2.6 DATUM
The vertical datum used for the mitigation plans is the National Geodetic Vertical Datum of 1988.
City of Renton 553-1779-014 (01/01)
Wetland Mitigation Banking Plan 2-4 February 2002
Miligafion Banking Plan.doc
A 1993 field assessment of the two mitigation banking sites indicated that both sites contain relatively low -
value seasonally perched wetlands that are generally composed of cottonwood (Populus balsamifera), red
alder (Alnus rubra), sahnonberry (Rubus spectabilis), willow (Salix spp.), and reed canarygrass (Phalaris
anwdinacea). The wildlife habitat value of the mitigation banking sites is limited by lack of habitat structure,
wetland classes, and buffers, although the wildlife habitat value of the large wetland on Site 1 (see Figure 2)
appears to be greater than that value at Site 2 (see Figure 3). Both sites support immature deciduous trees.
Habitat for many wildlife species (e.g., cavity -nesting birds) is limited by the relatively young age of the
forested portions of both sites and the relatively low species diversity within the plant communities. In
addition, there are no permanently wet areas on either site. The existing wetlands are seasonal in character
and possess relatively low functional capacity for floodwater storage and water quality improvement. The
wetlands are also artificial, and developed on nearly level areas or shallow depressions on top of fill and
generally occur at elevations 5 to 9 ft higher than neighboring water bodies (e.g., Springbrook Creek) and
historical ground surface.
Both sites have large areas in which reed canarygrass and introduced blackberry species (Rubus discolor-
procera, R. lacianatus) have become established. Both sites also have areas in which Scots broom (Cytisus
scoparius) grows. These undesirable plant species will continue to expand their abundance unless shaded by
taller vegetation, removed, or otherwise controlled. Site 2 shows less evidence of human use, but Site 1 is
frequently used by off -road vehicles, an activity that has resulted in significant disturbance to the landscape
despite efforts by the City to restrict entry for this purpose.
A significant amount of fill has been placed on both sites, with the depth of fill as great as 10 ft in some
places. This material generally has low organic content and consists of a variety of textures. Where clay and
silt contents are relatively high, seasonally perched water is present. Although soils in the wetland areas
show mottled coloring, the soils may have had hydric colors when deposited. Using a backhoe, the soil test
technician dug three holes on Site 1 and five on Site 2. The soil test locations are shown in Figures 2 and 3,
and the results are presented in Figures 4 and 5. Photographs of the soil test locations are provided in
Appendix C.
3.1 MITIGATION BANK SITE 1
Site 1 is 30.97 acres; its northwest corner is within the 100-year floodplain of Springbrook Creek.
Approximately one-third of the site has been cleared, or cleared and filled, over the past several years. In
about 1975 the site was cleared of all trees, and a historical meander of Green River on the site was filled,
creating localized wetlands (Hart Crowser 1991a). Fanning appeared to be the predominant activity on the
site until the early 1970s.
3.1.1 Wetland Delineation
Three wetland areas were identified and delineated on Site 1, ranging from 0.14 to 17.91 acres in size (David
Evans and Associates 1991a•, see Figure 2). The wetland communities typically occur in the relatively
undisturbed and depressed areas, and the majority of upland communities occur in elevated areas that have
been more recently filled. Topography on the site ranged from an elevation of 18 to 20 ft. Wetland J is a
0.14-acre shrub wetland, Wetland L is a 0.73-acre shrub wetland and wetland M is a 17.91-acre emergent,
shrub, and shrub -young -forested wetland. The Army Corps of Engineers confirmed the wetland boundaries
in 1996.
City of Renton 553-1779-014 (01/01)
Wetland Mitigation Banking Plan 3-1 February 2002
Mitigation Bwtbng Plan.dac
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Sandy Silty Filler Seepage
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Fine Sand Clay h/\/\/\! Black Sand Soil Characteristics on
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3.1.2 Vegetation Communities
Several vegetation communities occur on the site; these include upland meadow and shrub communities, a
wet meadow, and shrub and young -forested wetland (see Figure 2). The upland meadow communities are
variable in species composition, but in general are dominated by upland and facultative upland species.
Species common to the upland meadow community include: creeping bentgrass (Agrostis stoloneifera),
English plantain (Plantago lanceolata), velvet grass (Holcus lanatus), common tansy (Tanacetum vulgare,
hairy cats -ear (Hypochoeris radicata), soft chess (Bromus mollis), and Canada thistle (Cirsium arvense)
(David Evans and Associates 1991a).
The upland shrub community consists primarily of Himalayan blackberry and Scots broom (David Evans and
Associates 1991a). The Himalayan blackberry stands are nearly impenetrable and reach up to 15 ft tall. The
blackberry stands have overgrown vegetation described above in the upland meadow community, and below
in the seasonally wet meadow community.
The seasonally wet meadow portions of on -site wetlands are dominated almost exclusively by reed
canarygrass (David Evans and Associates 1991a). Secondary vegetation within the wet meadows includes
creeping bentgrass and common velvet grass.
The shrub and young -forested wetland community is dominated by young willows and black cottonwood
with some western crab apple (Malus fusca), red -osier dogwood (Corpus stolinifera), and Douglas spires
(Spiraea douglasii). The herbaceous layer consists of creeping bentgrass, creeping buttercup (Ranunculus
repens), soft rush (Juncus effusus), and common horsetail (Equisetum arvense).
3.1.3 Soils, Hazardous Material, and Geotechnical Information
3.1.3.1 Soils
The Soil Survey for King County (Snyder et al. 1973) mapped three different soils on Site 1: Puyallup fine
sandy loam, Woodinville silt loam, and Puget silty clay loam. Puyallup fine sandy loam is a well -drained
sandy loam soil formed in alluvium generally found on natural terraces adjacent to streams in valleys. Puget
soils are non-hydric, however, hydric inclusions of Woodinville and Puget soils can occur. Woodinville silt
loam is a hydric soil composed of poorly drained material. These soils formed in alluvium on stream
bottoms. This soil ranges from silt loam to silty clay loam with thin lenses of very fine sandy loam and
loamy sand or peat. David Evans and Associates (1991a) confirmed this soil unit on the western,
northwestern, and eastern portions of the site. The third soil unit, Puget silt clay loam, is a hydric soil which
developed in small depressions in river valleys. The soil contains silty clay loam to silt loam stratified with
silt loam, silty clay, and fine sand. This soil unit is mapped in a small portion of the site along the western
edge within the historic influence of the Green River.
Fill soils occur on approximately one-third of the site, with the thickness of fill ranging from 12 to 48 inches
in depth. A 4-foot -high mound of fill material covers approximately 1 acre in the southeast portion of the
site.
3.1.3.2 Hazardous Materials
A preliminary environmental site assessment indicated that the source of fill material brought onto Site 1 to
fill the meander is unknown without further investigation (Hart Crowser 1991a). The chemical constituents
of this fill material are also unknown. A second environmental site assessment prepared by Golder and
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Associates (1992), observed that there was no obvious evidence of significant dumping or related chemical
contamination on the site.
3.1.3.3 Geotechnical Information
Several evaluations of soil conditions have been made at the mitigation site. Available data include the Soil
Conservation Service soil survey (Snyder et al. 1973) and test pit data collected by Parametrix, Inc.
(Appendix C), Dames & Moore (1995; Appendix H) and Hong West (1997; Appendix 1).
Parametrix investigated soils at three locations on Site 1 in the summer of 1993. Test location 1, excavated
near wetland flag M-51 (David Evans and Associates 1991a [see Figure 2]), was at a ground surface
elevation of approximately 18 ft (see Figure 4). Fill occurred from the surface to an elevation of about 14 ft
and consisted of a silty sand with prominent mottles. Below the fill, soils consisted of a fine silty sand. The
water table occurred at about 9 ft below the ground surface.
Test location 2 was excavated in the northwest comer of the site at a ground elevation of approximately 18 ft
(see Figure 2). At this site, soil characteristics were similar to those observed in test location 1 (see Figure 4).
Fill occurred from the surface to an elevation of at least 11 ft. Saturated silty sand mixed with mottles and fill
occurred below 16 ft. The depth of fill was estimated to be at least 5 ft.
Test location 3 was excavated in the southeast corner of the site at a ground elevation of approximately 18 ft
(see Figures 2 and 4). Fill occurred from the surface to an elevation of 14 ft. Below 16 ft was a 3/4 inch deep
iron oxide layer followed by a silty fine sand fill layer. Woody debris (natural) was observed at 14 ft. Water
seepage was evident at 7 ft. The depth of fill was estimated to be at least 4 ft.
Dames & Moore (1995; Appendix H) conducted a geotechnical investigation of Site 1 which included
examination of sub -soil conditions in five test pits. Fill was located in test pits 1, 3, and 4 and ranged from 2
to 3 ft in thickness. The fill materials consisted of gravel, silty sand, and silt. The fill soils were underlain by
native soils which include inter -bedded layers of silt, silty sand, and sand. In general, the upper 4 to 10 ft of
deposits is a soft silt underlain by sand. An exception to this general condition occurred in the center of the
site, where the surface fill material was underlain by sand (test pit #3).
3.1.4 Hydrology
The existing wetlands on Site 1 are maintained by direct precipitation. A north -south oriented drainage ditch
near the west edge of the site provides surface drainage for property located south of the site and portions of
the site itself, but does not overflow into wetlands. This ditch contains standing water for much of the year.
Monitoring well and test pit data indicate that seasonally high groundwater remains several feet below the
surface when at its highest level (late winter). Water leaves Site 1 through evapotranspiration, infiltration, or
in some locations, limited surface runoff to the drainage ditch.
Site 1 is located within an approximately 300-acre subbasin that is tributary to Springbrook Creek. Flows
within the subbasin pass through an 18-inch culvert located at the eastern edge of Wetland W-12a. This
culvert passes through the fill of an old road bed (constructed in the 1970's) which generally blocks outflow
from Wetland W-12a. At its lowest point, the top of the berm is elevation 14.6 ft, and except under extreme
flood events (such as occurred on February 8, 1996). The berm prevents floodwaters of Springbrook Creek
from entering Wetland W-12a.
As part of the mitigation for wetland impacts resulting from the City's Oakesdale Ave. Extension Project,
Ecology is requiring the removal of most of the berm separating Wetlands 12-a and 12-b, including the 18
inch culvert. Both wetlands will be combined to form one large, continuous wetland.
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3.1.5 Functional Assessment
A functional assessment of wetlands on Site 1 was prepared using the functional evaluation methodology
described in Appendix B. The results of the assessment (Table 1) provide information on the functions that
the existing wetlands provide, and identifies functions that are absent, degraded, or that could be provided
with the proposed site plans for the mitigation banking sites. These results provide the basis for determining
the value of the functions established by creating additional wetland habitat, and the baseline information that
will be used to compare the success of the mitigation wetlands.
Table 1. Summary of Functional Evaluation of Wetlands on Mitigation Banking Site 1
Ch aracteristiefFunction
Wetland Condition
Buffer Condition
Biological Support
Water Quality
Flood and Stormwater Desynchronization
Groundwater Exchange
Support of Base Flow
Cultural Value
Shoreline Stabilization
3.1.5.1 Wetland Condition
Rating
Existing Conditions Proposed Conditions
Low Medium High Low Medium High
X X
X X to X
X to X X
X
X
X
X
to X
X
X
X
X
to X
X
X
to X
N/A
N.� A
A low rating for wetland condition reflects that the wetland has been subject to human disturbance and
the current ecological condition of the entire wetland is highly modified. Site 1 has been cleared of native
vegetation, filled, and colonized by several invasive vegetation communities. The condition of Site 1
could be improved by controlling exotic and invasive species, reestablishing wetland hydrologic
conditions affected by fill, replanting with native wetland plant communities, and removing other human
caused disturbances.
3.1.5.2 Buffer Condition
The existing buffer condition of the site is low due to past and ongoing land uses. To the north of the site,
shrub and forested wetland communities provide higher quality buffer and habitat functions. Undeveloped
land also provides a buffer to the south of the site. Increasing vegetation density along the southern and
western perimeter of the site will increase the buffer capacity in these areas. While the BN railroad track
west of the site and Oakesdale Avenue limit the ability of off -site areas to function as wetland buffers,
plantings along the perimeter of the site would increase the ability of on -site vegetation to protect the site
from adjacent land uses.
3.1.5.3 Biological Support
The biological support function is considered to be low to moderate. The wetland communities provide
limited structural diversity (i.e., the types and diversity of plant communities and habitat types present) and
this condition reduces the species diversity of the site. No unique or water -dependent species are present on
the site. The forest and shrub communities provide cover and nesting or perching sites for small mammals
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and birds. The upland and seasonally wet meadow areas provide habitat for small mammals that are prey to
larger mammals (e.g., coyote) and raptors (e.g., red-tailed hawks). The functional evaluation indicates that
the value of the biological support function would be higher by increasing the habitat structure and
interspersion of habitats and habitat types (creating greater edge effects) and adding special habitat features.
3.1.5.4 Water Quality Improvement
The functional evaluation indicates a high potential for improving water quality in the existing wetlands.
However, the three wetlands that make up Mitigation Bank Site 1 do not contribute to improving downstream
water quality or filtering of contaminants from adjacent non -point and point source pollutants because there is
little or no flow of urban runoff from off -site areas into the wetland. The wetlands' usefulness in providing
significant water quality function would increase, however. by directing water contained in the drainage ditch
near the southwest corner of the site to on -site wetlands.
3.1.5.5 Stormwater and Flood Water Desynchronization
The wetlands are not in any floodplain and do not receive runoff from upslope areas, and are thus rated low
for this function. This function could be increased to high by connecting the existing drainage ditch into the
mitigation design. Thus, upstream storm runoff that enters the drainage ditch would be attenuated on the
mitigation site.
3.1.5.6 Groundwater Exchange
Although a potential aquifer occurs deep below the site, the existing wetlands are underlain by slowly
permeable consolidated fill, which causes seasonally perched water. This condition limits the ability to
provide significant groundwater recharge functions. Created wetlands on the site are not expected to
contribute significantly more than undeveloped uplands or other wetland to groundwater exchange.
3.1.5.7 Support of Base Flow
All three wetlands have characteristics that indicate seasonal hydrology and ponding which may augment
base flow to Wetland W-12a and Springbrook Creek. Establishing direct connectivity between the mitigation
banking site and the City wetlands and Springbrook Creek could increase the value of this function.
3.1.5.8 Cultural Value
The opportunity for Site 1 to provide recreational and visual opportunities, or aesthetic appreciation for the
natural environment, is low because of the existing conditions of the site (i.e., lack of habitat diversity and
lack of access). Opportunities for cultural values associated with wetlands would increase by incorporating
public access and a trail system into the City's open space and parks program.
3.1.5.9 Shoreline Stabilization
This function is not applicable to Site 1.
3.1.6 Wetland Rating
3.1.6.1 City of Renton
Under the City's wetland classification system, the wetlands qualify as Category 3 wetlands because they
are disturbed from (1) clearing and filling, (2) hydrologic alterations, and (3) the presence of fill.
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3.1.6.2 Washington Department of Ecology
Wetland M on Site 1 is classified as a Category 11 wetland according to the Washington State Wetlands
Rating System, Western Washington (Ecology 1993). Wetlands J and L are Category 1H wetlands.
3.2 MITIGATION BANK SITE 2
Site 2 is 13.93 acres, of which 6.69 acres are wetland and 7.24 acres are upland. The site consists
primarily of herbaceous perennial grasses and forbs, annual forbs, and early successional shrub and
forested wetlands. Forested wetlands are dominated by black cottonwood (see Figure 4; David Evans and
Associates 1991b). The entire site was filled during the original fill in 1978 and the topography is
relatively flat, with elevations ranging from 15 to about 18 ft. Grading work on the site has resulted in
small depressions that contain compacted soil, some of which pond water. The site is not within the 100-
year floodplain (City of Renton 1995).
3.2.1 Wetland Delineation
Two wetlands totaling 6.69 acres were identified and delineated by David Evans and Associates (1991b).
Willow, black cottonwood, and Himalayan blackberry dominate the northern wetlands. The wetlands are
classified as palustrine shrub wetlands. These wetlands occur on fill and are not regulated by the Army Corps
of Engineers (ACOE 1996; Appendix G).
3.2.2 Vegetation
The shrub plant community consists of black cottonwood saplings and willow shrubs. Salmonbenry and
Himalayan blackberry shrubs are also present. Herbaceous plant cover within the shrub community is sparse,
but grasses and forbs occur occasionally. The emergent wetlands consist of shallow depressions dominated
by bentgrass, foxtail (Alopecurus geniculatus), soft rush, and reed canarygrass. Upland forbs and grasses
include clover (Trifolium repens), Kentucky bluegrass (Poa pratensis), tall fescue (Festuca arundinacea),
quackgrass (Agropyron repens), and hairgrass (Airs caryophyellea).
3.2.3 Soils, Hazardous Material, and Geotechnical Information
3.2.3.1 Soils.
The Soil Survey for King County (Snyder et al. 1973) mapped the soils on Site 2 as Woodinville silt
loam. However, the majority of the site consists of urban fill. The type of fill and its low permeability
has lead to the development of hydric soil conditions within the fill.
3.2.3.2 Hazardous Materials
A preliminary environmental site assessment made by Kennedy/Jenks/Chilton (1989) indicated that a small
potential existed for contamination to enter the site via groundwater. A site reconnaissance did not identify
significant potential for environmental contamination from current or past site use. An environmental site
assessment (Hart Crowser 1991b) indicated that sediment samples collected from Springbrook Creek south of
SW 27th Street (between Lind Avenue and Oakesdale Avenue SW) had contamination below the Model
Toxic Control Act Method A cleanup levels and below the Washington Administrative Code Sediment
Criteria. No remedial activities were recommended for this area.
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3.2.3.3 Geotechnical Information
Five soil test pits were examined on Site 2 (see Figure 3). The results of this analysis are summarized below.
Soil test pit 1 was excavated in an upland area adjacent to Springbrook Creek at an elevation of about
19.5 ft. In general, the soils were uniform from the surface to an elevation of about 10.5 ft (see Figure 5).
The soils consisted of sandy, silty fill. A blue -gray saturated clay layer was observed at an elevation of
about 10.5 ft and extended down to an elevation of about 9 ft. Concrete debris was observed at 4 ft 5
inches. No standing water was observed. The depth of fill was estimated to be approximately 9 ft.
Soil test pit 2 was also excavated in an upland area adjacent to an emergent wetland community at a
surface elevation of approximately 16.5 ft (see Figure 5). From the surface to an elevation of 12 ft, the
soil was sandy and lightly mottled with a thin, silty, clay layer observed at an elevation of about 14.5 ft.
At an elevation of 11.5 ft, the silty clay sediment was saturated and mottled. Blue clay was observed at
an elevation of 10 ft, followed by saturated silty clay to an elevation of 7 ft. A lens of organic material
with woody debris and black wet sand was observed below elevation 6.5 ft. Water was evident at
elevation 5.2 ft and seepage was evident at elevation 7 ft. Plant roots were evident as deep as an elevation
of 5.5 ft.
Soil test pit 3 was excavated in shrub wetland, at a surface elevation of 16 ft (see Figure 5). Mottled
sandy silt was evident at an elevation of 15 ft. The soils had more sandy texture above elevation 15 ft, but
below elevation 15 ft finer soil textures dominated. An oxidized iron zone was observed at elevation 14
ft. At elevation 11 ft, the soils consisted of damp clay with bright mottles. The depth of fill was
estimated to be 4.5 to 5 ft.
Soil test pit 4 was excavated in an upland area with a surface elevation of 15.5 ft (see Figure 5). The soil
consisted of sand and gravel fill with silt from the surface to an elevation of 11.5 ft. The historic A
horizon, composed of silty clay with mottles, occurred within a 10- to 12-inch band below the fill. Below
the historic A horizon was a 4-inch gleyed layer with strong mottles. Water seepage was observed at 7.5
ft. Clay was the dominant sediment to about elevation 4.5 ft. Below 4.5 ft the sediment was black, wet
sand. The depth of the fill was estimated to be 4 to 4.5 ft.
Soil test pit 5 was excavated in an upland area; it had a similar profile to test pit 4, and at a surface
elevation of 16 ft. Fill occurred from the surface to an elevation of about 13 ft (see Figure 5). This soil
horizon showed no wetland characteristics. The historic A horizon was observed to 12 inches below the
fill. Clay was the dominant soil texture below the historic A horizon. Seepage was evident at 8 ft. Black
sand was observed at an elevation of 5.5 ft. The depth of the fill was estimated to be 3 ft.
No differences were observed in the soil texture or composition within the top 3 to 4 ft between wetland
and upland areas. Wetlands have developed as a result of fine -textured fill material, which is able to
perch, and pond water.
Dames & Moore (1995; Appendix H) conducted a geotechnical investigation of Site 2. This study
examined five test pits and found fill was present in all test pits. The fill is underlain by alluvial soils, the
upper 4 to 10 ft of which was found to be silt. The silt layer contains sand layers ranging from 2 to 2.5 ft
in thickness and thin layers of peat.
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3.2.4 Hydrology
The source of hydrology for the existing wetlands on Site 2 is largely precipitation. Wetlands on this site
do not appear to receive runoff from adjacent land and have no inlet or outlet. The elevation of the
wetlands are several ft higher the typical water elevation of Springbrook Creek (about 7.8 ft).
Northwest Hydraulic Consultants, Inc. (NHC) conducted a hydrologic analysis of flood frequencies of
Springbrook creek and evaluated changes to stream hydrology based on the proposed mitigation
(Appendix W. Additional hydrologic modeling of the creek is ongoing.
NHC used the hydrologic simulation program -Fortran model (HSPF) to determine flow under different
watershed conditions for Springbrook Creek as it passes the mitigation Site 2. The model predicted flood
flows of Springbrook Creek under current land -use to be 355 cubic ft per second (cfs) at bankfull
conditions (approximately the 2.0 year storm). At the 10, 25, 50, and 100-year floods, predicted flows are
570, 698, 803, and 917 cfs respectively, are .
3.2.5 Functional Assessment
The functions of the existing wetlands on Site 2 were assessed using the functional evaluation in Appendix B.
The results of this assessment (Table 2) indicate that the wetlands are generally of low quality.
Table 2. Summary of Wetland Functions Provided by Mitigation Banking Site 2
Rating
Existino Conditions
Proposed Conditions
Characteristic/Function Low Medium High Low Medium High
Wetland Condition
X
X
Buffer Condition
X
X to X
Biological Support
X
X
Water Quality
X
X
Flood and Stormwater Desynchronization
X
X
Groundwater Exchange
X
X
Support of Base Flow
X
X
Cultural Value
X
X
Shoreline Stabilization
N/A
X to X
3.2.5.1 Wetland Condition
The general condition of the wetland was rated as low, because the site has been impacted by a variety of
human activities. Alterations including filling, vegetation clearing, and diking of Springbrook Creek have
occurred on the site for the past 20 years. The wetland would receive a higher rating under the proposed
mitigation banking plan because fill material would be removed, human impacts would not be allowed, and
hydrologic conditions could be improved.
3.2.5.2 Buffer Condition
The condition of the buffer is considered poor. Oakesdale Avenue constitutes the western buffer of the site.
The presence of Springbrook Creek along the south and west sides of the site provides a connection to off site
habitats. Developed land (zoned industrial) currently provides a buffer to the north. The rating for the buffer
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condition would improve slightly over existing conditions by improving the buffer condition between
Oakesdale Avenue and the new wetlands, as well as along Springbrook Creek.
3.2.5.3 Biological Support
The ability of the existing wetlands to provide biological support is low, due to their small size, low plant
species diversity, lack of habitat interspersion, early successional state, ongoing disturbances, and lack of
hydrologic connectivity with Springbrook Creek. In addition, observations by David Evans and Associates
(1991b) indicated that very few animals were using the site. The proposed banking plan for Site 2 would
increase the number of habitat types, provide habitat interspersion, increase structural diversity, and provide a
direct connection to Springbrook Creek.
3.2.5.4 Water Quality
Since there appears to be little or no surface water flow onto the site, and the wetlands are not in any
floodplain, they have little ability to improve water quality. The proposed plan would allow floodwater from
Springbrook Creek to enter the site thereby allowing potential contaminants to be removed by the wetland.
3.2.5.5 Flood and Stormwater Desynchronization
The on -site wetlands do not provide flood or stormwater attenuation due to their small size, lack of
hydrologic connections, and elevation above any floodplain. Based on the proposed banking plan, the site
would receive a high rating for this function because the proposed connection to Springbrook Creek would
provide flood storage.
3.2.5.6 Groundwater Exchange
The wetlands are underlain by slowly permeable compacted fill. Although a potential aquifer is under the
site, the presence of a confining layer of consolidated clay and fill over the aquifer significantly limits the
groundwater exchange function. The mitigation banking plan is not expected to alter the function of this
site relative to groundwater exchange.
3.2.5.7 Support of Base Flow
The existing wetlands are isolated from a surface Water system and do not support the base flow of
Springbrook Creek. The proposed plan would allow flood and storm waters to be temporarily stored on the
site, but relatively rapid release following flood events would not augment base flows of the creek.
3.2.5.8 Cultural Values
A low rating for cultural value results from an absence of scenic diversity, open water, and public access
to the site. The proposed plan would provide for passive recreation, educational opportunities, and a trail
link to the City's park system.
3.2.5.9 Shoreline Stabilization
The wetlands do not provide shoreline stabilization functions because they are isolated from any shoreline
area. A direct connection would be established between Springbrook Creek and the site under the
proposed plan. The site would attenuate energy from flood and stormwater in the creek, and help in
preventing downstream stream bank erosion.
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3.2.6 Wetland Rating
3.2.6.1 City of Renton
The wetlands on Site 2 are classified as Category 3 wetlands (see Table 1, Mitigation Banking Program,
and Parametrix 2002).
3.2.6.2 Washington Department of Ecology
The wetlands are rated as Category III wetlands using the Washington State Wetlands Rating System,
Western Washington (Ecology 1993).
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4. MITIGATION APPROACH
4.1 MITIGATION SEQUENCING
Private and public projects that may impact wetlands under the City's jurisdiction are required to comply
with mitigation sequencing as identified in the City of Renton's Wetland Ordinance (Appendix A). The
ordinance requires that applicants evaluate alternative methods of developing the property using the
following criteria in this order:
• Avoid any disturbances to the wetland or buffer;
• Compensate for any wetland or buffer impacts;
• Minimize any wetland or buffer impacts;
• Restore any wetlands or buffer impacted or lost temporarily; and
• Create new wetlands and buffers for those lost.
In implementing its ordinance, the City recognizes that there is flexibility in interpreting these guidelines on a
case -by -case basis for projects participating in a mitigation bank.
In addition, projects using the mitigation bank that require approval by the Army Corps of Engineers under
Section 404 of the Clean Water Act must comply with sequencing requirements of the 404 (b)(1) guidelines.
Interpretation and standards for meeting guidelines for compliance with City ordinance may differ from those
made to comply with federal requirements.
4.2 MITIGATION PLAN GOALS, OBJECTIVES, AND PERFORMANCE STANDARDS
The overall mitigation goal for the City of Renton Wetland Mitigation Banking Plan is to:
Establish about 20 acres of wetland mitigation and about 24 acres of enhanced wetland
and buffer habitat. The wetlands will include four wetland classes and upland forested
buffer that will provide food chain support and habitat connectivity to terrestrial and
aquatic wildlife. The wetlands will provide hydrologic functions such as
stormwater/flood flow retention and quality improvement. (Incorporation of the sites into
park and recreation plans will result in public access and the function of the sites as
education cultural values.)
Establish wetlands that meet the City of Renton criteria for Category 1 (Very High Quality)
wetlands. These wetlands will be greater than 10 acres in size and contain at least 3 vegetation
classes, one of which is open water.
To achieve this, the following specific objectives have been developed:
4.2.1 Mitigation Banking Site 1
4.2.1.1 Water Regime
• The wetland will provide approximately 10 acre-ft of stormwater storage.
• The wetland will contain a hydrologic connection to Wetland W-12a and Springbrook Creek.
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4.2.1.2 Vegetation Structure
• The wetland will consist of about 2.9 acres of seasonally flooded emergent, 5.7 acres of shrub,
and 1.4 acres of forested wetland plant communities.
• The new wetland will be integrated with vegetation enhancement of about 20 acres of existing
upland and wetland areas.
4.2.1.3 Habitat Attributes
• Forested components of the mitigation site will provide the structural elements for resident
wildlife (birds and small mammals) and migratory birds, including a mixed deciduous and
coniferous canopy, understory shrub canopy, and herbaceous ground cover.
• Heterogeneity between upland and wetland communities will provide resting, feeding, and
breeding habitat for aquatic fauna, terrestrial fauna, water fowl, and amphibians.
• Woody debris (downed logs, snags, and stumps) will provide habitat diversity.
• The upland buffers will screen the mitigation wetland from adjacent uplands and roads.
4.2.2 Mitigation Banking Site 2
4.2.2.1 Water Regime
• The wetland will provide up to 50 acre-ft of flood storage.
• The wetland has a surface hydrologic connection to Springbrook Creek.
4.2.2.2 Vegetation Structure
• The wetland will consist of 2.0 acres of emergent, 1.4 acres of shrub, and 6.4 acres of forested
vegetation classes.
• Wetland plant communities will be protected and enhanced by about 4 acres of forested upland
buffer.
4.2.2.3 Habitat Attributes
• Forested components of the mitigation site will provide the structural elements for resident
wildlife (birds and small mammals) and migratory birds, including a mixed deciduous and
coniferous canopy, understory shrub canopy, and herbaceous ground cover.
• Heterogeneity between upland and wetland communities will provide resting, feeding, breeding
habitat for aquatic fauna, terrestrial fauna, water foal, and amphibians.
• Woody debris (downed logs, snags, and stumps) will provide habitat diversity.
• The upland buffers will screen the mitigation wetland from adjacent uplands and roads.
• Hydrologic connectivity between Site 2 and Springbrook Creek will allow for the downstream
transport of organic carbon, thereby assisting in the support of instream food webs.
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4.3 PERFORMANCE STANDARDS
Performance standards for wetlands constructed at the mitigation bank sites will be used to determine if the
sites have been adequately constructed and if their ecological functions have been achieved. Performance
standards will be evaluated by measuring variables and determining if standards and objectives have been
met.
4.3.1 Mitiaation Banking Site 1
4.3.1.1 Water Regime
Objective: Provide stormwater storage functions.
Performance Standard: The wetland will provide approximately 10 acre-ft of stormwater storage. The
wetland will discharge through a surface water connection to Wetland W-12a.
Methods: The site will be graded to establish wetland depressions and connecting drainage ways at
elevations and grades sufficient to promote water storage. Grading plans, hydrologic analysis, and
monitoring data will demonstrate that the wetland collects runoff from the adjacent surface water sources (i.e.
a drainage ditch) and provides a minimum of 10 acre-ft of stormwater storage. Grading plans and monitoring
will demonstrate that surface water drains from the mitigation bank site to the natural wetland W-12a, which
connects to Springbrook Creek.
4.3.1.2 Vegetation Structure
Objective: Three types of wetland vegetation will be established.
Performance Standard: The wetland will consist of about 2.9 acres of open water/ seasonally flooded
emergent, 5.7 acres of shrub, and 1.4 acres of forested wetland plant communities.
Methods: Grading of the site will create topographic variability and hydrologic conditions suitable for
native forest, shrub, and emergent wetland plant species.
Objective: Upland vegetation in areas adjacent to the wetland will be enhanced to protect wetlands and
improve upland wildlife habitats.
Performance Standard: Vegetation enhancement of about 20 acres of adjacent upland and wetland
areas will occur.
Methods: Invasive plants, primarily blackberry will be controlled. Where a deciduous tree canopy is
present, conifer saplings will be planted in the understory. In open areas where trees are absent, they will be
planted at densities of about 200 /acre. Native shrubs will be planted in forest understory areas where they
are currently absent..
4.3.1.3 Habitat Attributes
Objective: Forested communities will provide the structural elements for resident wildlife (birds and
small mammals) and migratory birds, including a mixed deciduous and coniferous canopy, understory
shrub canopy, and herbaceous ground cover.
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Performance Standard: Forested plant communities will be multi -structural. While deciduous species
are predominant, a minimum of 25 percent of the canopy individuals will consist of coniferous species.
Understory shrub species will occur in a minimum of 50 percent of the forest zones. Herbaceous
groundcover shall consist of non-invasive plant species, but may include non-native grass or forb species
used in hydroseed mixes to reduce colonization by blackberry or reed canarygrass.
Methods: Methods for water regime and vegetation structure will achieve this objective. Where necessary,
replanting and invasive species control will be implemented.
Objective: Heterogeneity between upland and wetland communities will provide resting, feeding, and
breeding habitat for aquatic fauna, terrestrial fauna, waterfowl, and amphibians. Woody debris (downed
logs, snags, and stumps) will provide habitat diversity.
Performance Standard: Topographic variation, including micro -topographic features, non -linear edges
between planting zones, and spatial variation in planting will be present, as verified by analysis of as -built
mitigation plans.
Methods: Design of the mitigation projects will include placement of woody debris and micro -topography
(i.e. mound and depressions 1-3 feet in height). as habitat features. The objectives for vegetation structure
and the proposed planting plan provide for spatial heterogeneity.
Objective: Upland buffers will screen the mitigation wetland from adjacent uplands and roads.
Performance Standard: Natural vegetation in upland buffers will be enhanced with tree and shrub
species to achieve densities exceeding 250 trees per acre and 400 shrubs per acre.
Methods: Enhancement planting in upland buffers will augment existing vegetation to achieve densities
of 250 trees and 400 shrubs per acre.
4.3.2 Mitigation Banking Site 2
4.3.2.1 Water Regime
Objective: Provide 50-acre feet of stormwater storage function.
Performance Standard: The wetland will provide approximately 50-acre-ft of stormwater storage. The
wetland will discharge through a surface water connection to Springbrook Creek.
Methods: The site will be graded to establish wetland depressions and connecting drainage ways at
elevations and grades sufficient to promote floodwater storage from Springbrook Creek.
4.3.2.2 Vegetation Structure
Objective: Three types of wetland vegetation will be established on the mitigation site.
Performance Standard: The wetland will consist of 2.0 acres of open water/ seasonally flooded
emergent, 1.4 acres of shrub, and 6.4 acres of forested wetland plant communities.
Methods: Grading of the site will create topographic variability and hydrologic conditions suitable for
native forest, shrub, and emergent wetland plant species.
».s-t 11Y_UJ * i vliw �
City of Renton
February 2002
Wetland Mitigation Banking Plan 44
Mitigation Banking Plan.dac
Objective: Upland vegetation in areas adjacent to the wetland will be enhanced to protect wetlands and
improve upland wildlife habitats.
Performance Standard: Vegetation enhancement of about 20 acres of adjacent upland and wetland
areas will occur.
Methods: Invasive plants, primarily blackberry will be controlled. Where a deciduous tree canopy is
present, conifer saplings will be planted in the understory. In open areas where trees are absent, they will be
planted at densities of about 200 /acre. Native shrubs will be planted in forest understory areas where they
are currently absent.
4.3.2.3 Habitat Attributes
Objective: Forested communities will provide the structural elements for resident wildlife (birds and
small mammals) and migratory birds, including a mixed deciduous and coniferous canopy, understory
shrub canopy, and herbaceous ground cover.
Performance Standard: Forested plant communities will be multi -structural. While deciduous species
are predominant, a minimum of 25 percent of the canopy individuals will consist of coniferous species.
Understory shrub species will occur in a minimum of 50 percent of the forest zones. Herbaceous
groundcover shall consist of non-invasive plant species, but may include non-native grass or forb species
used in hydroseed mixes to reduce colonization by blackberry or reed canarygrass.
Methods: Methods for water regime and vegetation structure will achieve this objective. Where necessary,
replanting and invasive species control will be implemented.
Objective: Heterogeneity between upland and wetland communities will provide resting, feeding, and
breeding habitat for aquatic fauna, terrestrial fauna, waterfowl, and amphibians. Woody debris (downed
logs, snags, and stumps) will provide habitat diversity.
Performance Standard: Topographic variation, including micro -topographic features, non -linear edges
between planting zones, and spatial variation in planting will be present, as verified by analysis of as -built
mitigation plans.
Methods: Design of the mitigation projects will include placement of woody debris and micro -topography
(i.e. mound and depressions 1-3 feet in height). as habitat features. The objective for vegetation structure and
the proposed planting plan provides for spatial heterogeneity.
Objective: Upland buffers will screen the mitigation wetland from adjacent uplands and roads.
Performance Standard: Natural vegetation in upland buffers. will be enhanced with tree and shrub
species to achieve densities exceeding 250 trees per acre and 400 shrubs per acre.
Methods: Enhancement planting in upland buffers will augment existing vegetation to achieve densities
of 250 trees and 400 shrubs per acre.
City of Renton 553-1779-014 (01/01)
Wetland Mitigation Banking Plan 4-5 February 2002
Mitigation Banking Ptan.doc
5. PRELIMINARY SITE DESIGN
The preliminary site designs for Sites 1 and 2 are shown in Figures 6 and 7. The preliminary site plans
illustrate the proposed changes in topography and hydrology; proposed vegetation distribution and
structure; location of habitat types and the proposed buffer; and section drawing that shows the
relationship of topography, hydrology, and vegetation.
5.1 TOPOGRAPHY
Excavation on about 10 acres of Site 1 is proposed to create new wetland areas up to 6 ft below existing
grades. The planned excavation establishes a broad wetland drainageway connecting the existing ditch on
the west side of the site to Wetland W-12a.
Excavation of about 9.8 acres of Site 2 will occur to depths up to 15 ft below existing grades. This
grading will connect the new wetland to the Springbrook Creek channel and floodplain.
On both sites, the grading will allow for a variety of wetland communities to be established within each
site; the changes will also result in the removal of significant amounts of material from each site. An
estimated 100,000 cubic yards of material could be removed from Site 1 and about 150,000 cubic yards
from Site 2 (Appendix Q.
5.2 SOURCE OF WATER
Wetland hydrology for both sites will be provided by a variety of sources, but seasonally high groundwater
tables and precipitation are the most important sources for the two mitigation sites.
In addition to high groundwater and precipitation, the proposed source of water for Site 1 includes the
drainage ditch at the southwest corner of the site (see Figure 6) and on -site precipitation. An inlet at an
elevation of about 17 ft would be constructed and a notched weir outlet at an elevation of about 12 ft is
proposed at the northeast corner of the site.
While seasonally high groundwater would be present at Site 2, Springbrook Creek and on -site precipitation
(see Figure 7) will also provide hydrology. The site will be graded to establish a hydrologic connection
between the wetland and Springbrook Creek. Seasonal flooding of the wetland by the creek will augment
flooding in the wetland.
5.3 SOILS
Generally on site soils are expected to provide the planting media for the planned wetland communities.
Development of wetland vegetation would probably be enhanced if the upper 12 inches of on -site soils were
amended with organic matter. In addition, soils in areas designated as forested .wetland are likely to receive
much of their wetland hydrology from precipitation. These areas must have relatively low permeability
subsoil that remains saturated during winter and early spring months. In some locations, the existing subsoil
may be amended or compacted to reduce its permeability.
City of Renton 553-1779-014 (01/01)
Wedand Mitigation Banking Plan 5-1 February 2002
Mitigation Banking Plan.doc
b
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Z
LEGEND
Proposed contours
Existing contours
Existing wetland boundary
NOTES
1. Existing contours rounded to nearest 0.1 foot based on 0.5
meter (1.64) topography provided by the City. Proposed contours of
1 foot intervals.
2. Planting zones are based on base Flow averages o' the ditch and
three ground water wells during Dec. and Jun. See section A —A'.
3. Existing wetlands (approx. 13.1 cc), uplands and buffers (approx.
4.7 cc) to be enhanced with Zone 4 and 5 plantings. Exact areas
and quantities to be determined.
4. Soils in proposed wetlands may require compaction or
amendment to reduce permeability.
PLANTING PLAN
WETLAND PLANTING ZONES
ZONE 1 (approx.
2.9 oc)
Sclen name
HERBS
Angelica genuflexa
CcgID name
HERBS
Kneeling angelica
Oenonthe sarmentosa
Veronica americans
Water —parsley
American brooklime
GRAMINOIDS
GRAMINOIDS
Alopecurus geniculatus
Water foxtcif
Carex obnupto
Slough sedge
Carex stipato
Sawbeok sedge
El hors palustris
Common spike—rush
Glycerlo elate
Glycerin occidentalls
Toll manna grass
Westem manna grass
Juncus bufonlus
Toad rush
Juncus ensifolius
Dagger —leaf rush
Jun. tenuis
Slende, rush
Scirpus ocutus
Hard —item bulrush
Scirpus microcarpus
Small --fruited bulrush
Sparganium emersum
Norrow—leaf burreed
ZONE 2 (approx.
5.7 oc)
®
Salentlfic name
Comus stolonifera
cyan name
Red —osier dogwood
Salix lasiandro
Pacific willow
Salix sitchensls
Sitka willow
Salix scouleriana
Scouler's willow
Spiraeo douglasii
Douglcs spireo
ZONE 3 (approx.
1.4 ac)
Scien tlfic name
Alnus rubro
Common name
Red older
Fraxinus latifolia
Oregon ash
Malus fusca
Western crobopple
Populus trichocarpo
Black cottonwood
Rhamnus purshiona
Cascara
ZONE 4 (Buffer/ enhancement plantings)
Scientific name
Acer circinatum
L,Qdl@on name
Vine maple
Coryfus comuto—collfomica
Hazelnut
Lonicero involucrato
Twinberry
Rosa pisocarpc
Clustered rose
Rubus spectabllls
Salmonberry
Picea sitchensis
Sitka spruce
Thuja plicate
Western red cedar
Tsugo heterophylla
Pacific hemlock
UPLAND PLANTING ZONE
ZONE 5 (Buffer/ enhancement plantings)
Scientific name Amon name
Rosa nutkano Nootka rose
Ribes brocteosum Stink currant
Sombucus rocemosa Red elderberry
Acer macrophyflum Bigleaf maple
Crataegus douglasii Black hawthorn Pseudotsuga menziesii Douglcs Figure 6 a- Preliminary Grading
Fir
and Landscape Plan for
Mitigation Bank
Site 1
IN
0
V�
0
6 1 — 18 19' 1
5 �l
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11 12 3 14 16 1
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9 ...
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17 — —
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20:21
i 22
,&'N PROPOSED GRADING PLAN
SCALE: 1" = 100'
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� PROPOSED PLANTING ZONES
SCALE: 1" = 100'
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AVENUE
SECTION OF PROPOSED GRADING
AND PLANTING ZONES
4 3 2 1 2 1 3-
OOK
CREEK
VERTICAL: 1" = 10'
HORIZONTAL: V = 50'
LEGEND
Proposed contours
Existing contours
Existing wetland boundary
NOTES
1. Existing contours rounded to nearest 0.1 foot based on
0.5 meter (1.64) topography provided by the City- Proposed
contours at 1 foot Intermis.
2 Planting zones are based an base and storm flows for
Springbrook Creek See section A —A'.
PLANTING PLAN
WETLAND PLANTING ZONES
ZONE 1 (approx.
2.0 oc)
Scientific name
HERBS
Angelica genuflexa
Common name
HERBS
Kneeling angelica
Denanthe sarmentoso
Water —parsley
Veronica americono
American brooklime
GRAMINOIDS
GRAMINOIDS
Alopecurus geniculatus
Water foxtoll
Carox obnupto
Slough sedge
Carox stipato
Sawbeok sedge
Eleocharls polustris
Common spike—rush
Glycerla elato
Toll manna gross
Glycerla occidentolls
Western manna gross
Juncus bufonlus
Toad rush
Juncus ensifollus
Dogger —leaf rush
Juncus tenuls
Slender rush
Seirpup acutus
Hardstem bulrush
Scirpus microearpus
Small—frulted bulrush
Sporganium emersum
Narrow —leaf burreed
ZONE 2 (approx.
1.4 oc)
Scientific name
Comus stolonifera
Common name
Red —osier dogwood
Sal/x loslandra
PaclRc willow
Salix sitchensis
Sitka willow
Sollx scoulerlona
Scouler's willow
Spiroeo douglasll
Douglas spirea
ZONE 3 (approx.
1.9 oc)
Sclentfflc name
Ainus rubs
Common name
Red older
Fraxinus Iatifolia
Oregon ash
Mdus fusco
Western crobapple
Populus trichocarpo
Black cottonwood
Rhamnus purshlana
Cascara
ZONE 4 (approx.
4.5 ac)
Scientific name
Acer circinatum
Common name
Vine maple
Corytus comuto—colifomica
Hazelnut
Lonicero Involucroto
Twinberry
Roso pisocarpo
Clustered rose
Rubus spectobills
Salmonberry
Picea sitchensis
Sitka spruce
Thu)o plicato
Western red ceder
Teuga heterophylla
PaciRc hemlock
UPLAND PLANTING ZONES
ZONE 5 (approx.
4.0 ac)
Scientific name
Rosa nutkona
Common name
Nootka rose
Rlbes bracteosum
Stink currant
Sombucus rocemosa
Red elderberry
Acer macrophyllum
Crotaegus douglosll
Bigleaf maple
Black hawthorn
Pseudotsugo menziesll
Douglas Fir
Figure p
- Preliminary
Grading
and Landscape Plan for
Mitigation
Bank
Site 2
5.4 PROPOSED PLANT DISTRIBUTION
The plant species that are proposed for the two sites (Table 3) tolerate relatively wide fluctuations in
duration of soil saturation and inundation. In general, trees found in natural wetlands of the northwest
experience saturated soil and brief periods of inundation during the winter months. Thus, these species
will be used near the perimeter of the mitigation areas where seasonal saturation would be found. Herbs,
forbs, and grasses will be planted in elevations designated for emergent and open water habitat (see
Figures 6 and 7). The distribution of individual species will be determined based on the final grading
plan.
Following final design a final planting plan will be prepared that includes planting locations, the quantity
of each plant species, plant spacing, plant type (e.g., root stock, plugs), plant height, and planting
specifications. Plant survival on wetland mitigation sites can be improved using temporary irrigation
systems, which add flexibility to the season of year in which planting occurs and reduce mortality that
may occur during dry periods.
The final plan will also specify areas where invasive weeds will be removed or otherwise managed as part
of the planting plan. This management could include herbicide treatment, clearing and grubbing,
vegetation planting to out -compete undesirable species, or other methods.
Table 3. Candidate Plant Species Proposed for Wetlands and Buffers
Scientific Name Common Name Wetland Status`
Trees
Alnus rubra (1)
red alder
FAC
Crataegus douglasii (2)
black hawthorn
FAC
Fraxinus latifolia (3)
Oregon ash
FACW
Populus trichocarpa (1)
black cottonwood
FAC
Pyrus fusca (3)
western crabapple
NL
Rhamnus purshiana (3)
cascara
FACU
Salix sitchensis (2)
Sitka willow
FACW
Sa/ix lasiandra (1)
Pacific willow
FACW+
Salix scouleriana (1)
Scouler willow
FAC
Thuja plicata (2)
western redcedar
FAC
Shrubs
Cornus stolonifera (1)
red -osier dogwood
FACW
Lonicera involucrata (2)
black twinberry
FAC
Ribes bracteosum (3)
stink currant
FAC
Rosa nutkana (3)
Nootka rose
NI
Rosa pisocarpa (2)
clustered rose
FACU
Rubus spectabilis (1)
salmonberry
FAC
Sambucus racemosa (2)
red elderberry
FACU
Spiraea douglasii
Douglas spirea
FACW
Herbs
Angelica gennuflexa (3)
kneeling angelica
FACW
Aster occidentalis (2)
western mountain aster
FAC
Bidens cemua (2)
nodding beggar -tick
FACW+
Geum macrophyllum (3)
large -leaved avens
FACW
Lotus pinnatus (3)
meadow deer vetch
FACW
City of Renton 553-1779-014 (01/01)
Wetland Mitigation Banking Plan 5-5 February 2002
Mi igation Banking Plan.doc
Table 3.Candidate Plant Species Proposed Wetlands and Buffers (Continued)
Scientific Name Common Name Wetland Status*
Herbs (con't)
Ludwigia palustris (3)
water -purslane
OBL
Lupinus polyphyllus (3)
large -leaved lupine
FAC+
Oenanthe sarmentosa (2)
water -parsley
OBL
Polygonum persicaria (2)
smartweed
Rorippa nasturtium-aquaticum (2)
true water -cress
OBL
Rumex acetasella (3)
garden sorrel
NI
Rumex crispus (3)
curly doc
FACW
Tolmiea menziesii (2)
piggy -back plant
FACW
Pypha latifolia (1)
common cattail
OBL
Veronica americana (2)
American brooklime
OBL
Graminoids
Agrostis tenuis (1)
colonial bentgrass
NL
Alopecurus geniculatus (1)
water foxtail
FACW+
Carex obnupta (1)
slough sedge
OBL
Carex stipata (1)
sawbeak sedge
FACW
Eleocharis palustris (2)
common spike-rush
OBL
Elymus cinerrus (3)
giant wild rye
NI
Glyceria elata (3)
tall manna grass
FACW+
Glyceria occidentalis (3)
western mannagrass
OBL
Juncus bufonius (1)
toad rush
FACW+
Juncus ensifolius (1)
dagger -leaf rush
FACW
Juncus tenuis (1)
slender rush
FAC
Scirpus acutus (1)
hard -stem bulrush
OBL
Scirpus microcarpus (1)
small -fruited bulrush
OBL
Sparganium emersum (3)
narrow -leaf burreed
OBL
(1) Dominant Species
(2) Sub -dominant Species
(3) Associated Species
5.5 SECTION DRAWINGS
Cross sections and grading plans (see Figures 6 and 7) illustrate the vegetation communities, habitat
types, and general hydrologic conditions to be established on the mitigation sites. The cross section also
illustrates the proposed interspersion of habitat types and structural diversity that could be developed on
this site.
5.6 PUBLIC ACCESS
Locations of potential interpretive trails, trail entry signage, and an interpretive shelter on Site 1 and Site
2 must be developed. The interpretive trail for Site 1 should be limited to the eastern portion of the site
and would pass through wetlands. A bridge structure may be needed for portions of the trail within
wetland areas.
An interpretive trail for Site 2 could be located along the berm of Springbrook Creek; therefore, it would
not encroach on any wetlands. A bridge would need to be constructed across the breach in the berm to
provide public access from SW 34th Street to Oakesdale Avenue. Interpretive signage would be
unobtrusive. Signage could illustrate the pre- and post -conditions of the mitigation banking sites, the
City of Renton 353-1779-014 (01/01)
Wetland Mitigation Banking Plan 5-6 February 2002
Mitigation Banking Plan.doc
wetland habitat types, wildlife that use the wetlands, and/or document the other functions that wetlands
provide.
The trail systems would be integrated into existing and proposed trail systems within the City Parks
Department jurisdiction. Requirements under the American Disability Act for site access will need to be
evaluated during final site design.
City of Renton 553-1779-014 (01/01)
Wetland Mitigation Banking Plan 5-7 February 2002
Mitigation Banking Plan.dor
6. MONITORING PLAN
The following chapter describes a preliminary monitoring plan for evaluating the mitigation banking sites.
The anticipated parameters to be evaluated, methods of evaluation, and frequency of evaluation are
provided.
6.1 VEGETATION
Planted and naturally colonized vegetation will be evaluated to document plant establishment on the site
and to determine if the desired wetland plant communities are present. Monitoring will include all
wetland areas as well as designated buffer areas.
Monitoring will occur systematically with vegetation conditions measured along monitoring transects'.
The transects will be permanently marked and identified on survey maps showing the as -built conditions.
Data collection points will be established along transects within the wetland. At each data collection
point, a 0.25-m2 quadrae will be used to measure the following:
• Percent cover of each species and plant stratum (i.e. tree, shrub, or ground cover)
• The species composition (i.e., percent of each species, exotic or native, planted or colonized)
• Average height and general health of each planted species
• Vegetation structure (i.e. the heights and types of vegetation present)
• Density and size of snags and downed woody debris
Wetland vegetation will be monitored in early summer (between late June and July), during years 0
through 5, 7, and 10.
6.2 WATER REGIME
The hydrologic conditions of each mitigation site will be evaluated to determine if adequate hydrology is
present to support the desired wetland conditions and functions. Hydrologic measurements will include
measuring the depth of surface inundation, the presence of soil saturation in the rooting zone, and
estimating hydrologic flows into wetland areas from surface water sources (i.e., the ditch on Site 1, or
Springbrook Creek on Site 2). A crest stage gage will be installed and monitored monthly to determine
water surface elevations in open water areas. Hydrology in each wetland community type will be
measured at a fixed location monthly during the first 3 years following construction. Following this
period, the monitoring frequency will be evaluated to determine if additional measurements are necessary
to document that the wetlands have an adequate hydrologic regime.
6.3 SOILS
General soil parameters to be monitored at fixed points along the permanent transects include soil color
and organic content. Soil characteristics will be monitored once during the early portion of the growing
season (April/May) in years 0 through 5, 7, and 10.
'Transects are sampling lines crossing the mitigation area, where vegetation or other samples will be collected.
2Quadrats are specific areas established in the field to collect vegetation and other environmental data.
City of Renton 553-1779-014 (01 /01)
Wetland Mitigation Banking Plan 6-1 February 2002
Mitigation Banking Pian.doc
6.4 FAUNA
Wildlife monitoring on the mitigation sites (including the buffer) will include observations of birds and
mammals on the sites four times each year (spring, summer, fall, and winter). Observations of
amphibians that may use the sites will be documented through the presence of egg masses during late
winter or early spring. Observations will be made from fixed observation points as well as walk-through
surveys during years 0 through 5, 7, and 10. The observations will be made at the same time (e.g., from
6:00 am to 12:00 PM), during each sampling event. Between sampling years, observations will be made
within 4 calendar days of each other.
6.5 DEVELOPMENT OF HABITAT STRUCTURE
Monitoring the establishment of habitat structure will help determine whether suitable habitat is being
established. Measurements of habitat structure will include the number of structural levels and
distribution of habitats within the mitigation area. Monitoring parameters that provide information on the
development of habitat structure include tree structure, the density and size of habitat features (i.e., snags,
downed trees), canopy cover, number of structural levels, descriptions of adjacent land uses, and presence
of priority habitats and species (Washington Department of Wildlife 1991). These parameters are
discussed under monitoring for vegetation and water regime, above.
6.6 BUFFERS
Permanent transects will be established within the buffer area, and data collection points will be established
along these transects. At each data collection point, a 0.25-m2 quadrat will be used to measure the following:
• Percent cover of each species and plant stratum
• The species composition (i.e., percent of each species, exotic or native, planted or colonized)
• Average height and general health of each planted species
• Vegetation structure
Upland buffer vegetation will be monitored once between late June and July in years 0 through 5, 7, and
10.
6.7 SCHEDULE OF REPORTING MONITORING RESULTS
For each monitoring year, following implementation of the proposed monitoring schedule (Table 4), data
will be evaluated and results will be summarized in written monitoring reports. Following construction
and planting, an as -built report will be prepared to document the project conditions and any changes from
the final site plan that may have occurred during construction or planting. The as -built report will serve
as the baseline to compare results from subsequent monitoring efforts. Annual reports will be prepared
and submitted to the City by December 15 of each monitoring year.
City of Renton 553-1779-U14 (WN! )
Wetland Mitigation Banking Plan 6-2 February 2002
Mitigation Banking Plan.doc
Table 4. Proposed Schedule for Monitoring City of Renton Mitigation Banking Sites
Monitoring Parameters
0
(as built)
1
2
3
4
Year
5 6
7
8 9 10
Topography
X
X
X
X
X
X
X
X
Vegetation
X
X
X
X
X
X
X
X
Water regime
X
X
X
X
X
X
X
X
Soils
X
X
X
X
X
X
X
X
Fauna
X
X
X
X
X
X
X
X
Development of habitat
X
X
X
X
X
X
X
X
structure
Buffers
X
X
X
X
X
X
X
X
0
City of Renton 553-1779-014 (01/01)
Wetland Mitigation Banking Plan 6-3 February 2002
Mitigation Banking Plan.doc
7. SITE PROTECTION
7.1 LEGAL PROTECTION
As discussed in Section 2.3, the City owns both mitigation banking sites for the express purposes of
habitat conservation and mitigation. The City will identify the mitigation banking sites as wetland
management areas and prepare legal documentation indicating that the sites will be adequately protected.
7.2 MAINTENANCE AND CONTINGENCY PLAN
If, during the monitoring program, maintenance needs are identified that are required to ensure the
success of the mitigation project, they will be implemented. In addition, if performance standards for any
element of the mitigation plan are not met, contingency actions will be implemented.
For example, if the hydrology of the wetlands do not correspond to that of the performance standard,
actions (e.g., change the engineering design of the breach) will be taken to correct the deficiency. If
planted vegetation shows signs of stress, an evaluation can be conducted to determine the cause.
Replanting with other vegetation could occur after appropriate corrective action (such as soil amendments
or re -grading) has occurred. Alternatively, different plant species that are better adapted to the
environmental conditions of the site (e.g., elevations) could be planted.
The probability of success for the proposed wetland communities is high considering that wetland
communities, established on fill, currently exist on the site. Hydrologic conditions in the drainage ditch
on the western perimeter of Site 1 and Springbrook Creek, adjacent to Site 2, are considered important
elements to effective wetland creation on the mitigation banking sites.
Additionally, it should be noted that the City does not have to post a performance bond, but should
include funding within its annual budget monitoring and contingency actions.
City of Renton 553-1779-014 (01/01)
Wetland Mitigation Banking Plan 7-1 February 2002
Mingxwn Banking Plan.doc
8. IMPLEMENTATION
8.1 BACKGROUND
The wetland mitigation project will be implemented in accordance with the procedures and guidelines
outlined in the latest draft of Ecology's wetland mitigation bank certification rule dated August 14, 2000.
The purpose of the rule is to provide a potential bank sponsor certification that will satisfy state and
federal wetland mitigation bank requirements.
In 1997, the Washington legislature approved a law (90.84 RCW) allowing the creation of wetland banks
to compensate for the unavoidable loss of wetlands due to development. The law also required Ecology
to write a rule establishing an efficient, streamlined statewide process for certifying wetland mitigation
banks. The rule also simplifies the permitting process through the use of a multi -agency Mitigation Bank
Review Team (MBRT) with regulatory authority. The MBRT is composed of members from local
governments and businesses, as well as state and federal agencies such as the US Army Corps of
Engineers, Washington State Department of Fish and Wildlife, US Fish and Wildlife, Ecology, and
various agriculture and environmental groups and the tribes.
Currently, Ecology is conducting an internal environmental review of the pre -file draft rule. Once the
review is completed it will be published in the state register at which time four public hearings will be
held to be followed by a public comment period. The draft rule may then be modified to address the
responses received during the public comment period. In late summer of 2001, it is anticipated that
Ecology will file the final rule and the rule will become law.
8.2 THE CERTIFICATION PROCESS
8.2.1 Prospectus
The applicant or bank sponsor initiates the pre -application process by submitting a prospectus. The
prospectus is a conceptual proposal that initiates the dialogue with the various federal, state and local
agencies that make up the MBRT and includes the goals and objectives of the project.
The prospectus must contain sufficient information to allow Ecology and the MBRT to provide feedback
to the bank sponsor on the technical feasibility of the proposed bank and whether it complies with state
and local rules. The MBRT may identify additional information necessary to evaluate the proposed bank
such as supporting studies and other documentation.
8.2.2 Bank Instrument
After the MBRT reviews and comments on the prospectus, the bank must develop a draft bank instrument
for review by the MBRT and Ecology. This initiates the formal application process.
The purpose of the bank instrument is to describe in detail the physical and legal characteristics of the
proposed bank. This includes among other things, a statement of bank goals and objectives, potential
number of credits to be sold, performance standards, reporting and monitoring, functions and values to be
provided by the bank and method of financing.
In addition to the bank instrument, the applicant must complete and submit a bank certification
application form, State Environmental Policy Act (SEPA) checklist, and any applicable permit
applications such as a Joint Aquatic Resources Permit Application (JARPA) or Shoreline Master
Application, etc.
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Fi V L.1 V U L
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CITY OF RENTON, 1993
FILE: C: \ACADD\RENT FR
JOB:55-1779-07
W-32 = Wetland code from
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— — = Mitigation site boundary Existing Conditions
0 75 150
SCALE IN FEET Parametrix, Inc.T = Soil Test Pit Location (approximate) Mitigation Banking Site 2
8.3 ECOLOGY REVIEW AND DECISION/PUBLIC NOTIFICATION
Once in receipt of the formal application, Ecology will review it for completeness and notify the MBRT
which will convene to review the draft bank instrument. The MBRT will review and provide comments
on the technical requirements, terms and conditions of the certifications.
Concurrent with the MBRT review, Ecology must initiate a public notification and comment period. At
the end of this period, the MBRT evaluates the comments and may recommend changes to the bank
instrument to address public concerns. An additional comment period maybe required depending on the
extent of the initial comments.
If the all comments and concerns have been addressed to the MBRT satisfaction, Ecology will approve
the certification by signing the bank instrument. The local jurisdiction in which the proposed bank is
located is notified of Ecology's decision. If in concurrence with the decision, the local jurisdiction must
sign the bank instrument. Once signed by all three parties (Ecology, local jurisdiction and bank sponsor),
the bank instrument becomes officially certified and the wetland bank can be constructed pending
approval of all required permits.
8.4 ENVIRONMENTAL REVIEW/PERMITS
The following table includes all the required federal, state and local permits necessary to construct the
wetland mitigation bank:
Site 1
Site 2
SEPA Completed
No
Yes
Section 404 Required
Yes
Yes
Section 401 Required
Possible
Possible
ESA Compliance
Yes
Yes
Biological Evaluation
Yes
Yes
BPA Required
Possible
Yes
Shoreline Required
Possible
I Yes
SEPA for Site 2 was completed as part of the Final East Side Green River Watershed Project Plan and
EIS dated September 1997.
8.5 COST/FUNDING
The construction cost for Sites 1 and 2 can be found in Table 1 and Table 2, respectively. The total
construction cost for both sites is approximately 3.1 mullion dollars or $107,000 per acre of wetland
created including buffer. Additional funds would need to be appropriated to cover long term monitoring
and maintenance costs. The City will fund the construction of the bank and recover the cost through the
sale of bank credits. The primary source of funding would come from the sale of credits to wetland
customers. Additional funding may come from other City departments that may need to purchase credits
from the bank. Some of the costs to construct Site 2 could be offset by the sale of approximately 150,000
cubic yards of excavated fill material. The excavated material is primarily composed of structure fill and
depending on the quality, could be sold to local contractors who would use it for other projects. More
than likely however, a contractor would agree to excavate and haul the material offsite for free with no
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compensation to the City. This would still represent a substantial savings on the project of $300,000 to
$500,000.
Once the bank is complete and satisfies the performance standards required by the state, credits may be
sold to customers that require mitigation for construction impacts to wetlands within the service area.
The most likely bank customers interested in purchasing bank credits would be City and State agencies
and private developers. The City could use the bank credits as mitigation for wetland impacts to
transportation projects such as the SR-167/SW 27`h St. HOV/Strander Blvd. Connection Project. State
agencies such as Washington State Department of Transportation may find the mitigation bank their only
viable option when planned improvements to the I-405/SR-167 corridor are authorized for construction in
the future.
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9. PERFORMANCE
The City will appropriate money for the annual monitoring and maintenance of the mitigation site, and these
monies will also include reserve amounts to implement contingency actions if needed. This action will
provide the equivalent benefit of a performance bond and assure that required construction, monitoring,
maintenance, and adaptive management actions occur.
City of Renton 553-1779-014 (Olrol )
Wetland Mitigation Banking Plan 9-1 February 2002
Wiganoe BmAkg Plmdoc
City of Renton. 1995. Comprehensive Plan. Planning, Building and Public Works Department. Renton,
Washington.
City of Renton. 2000. Critical Area Ordinance, Ordinance Number 4835.
David Evans and Associates. 1991a. Wetland determination on the Renton #14 parcel. Prepared for
Glacier Park Company. Seattle, Washington. 20 pp. plus appendices.
David Evans and Associates. 1991b. Wetland determination on the Orillia block 8, lot 4 site (Renton
#8E parcel). Prepared for Glacier Park Company. Seattle, Washington. 14 pp. plus appendices.
Ecology (Washington State Department of Ecology). 1993. Restoring wetlands in Washington. A
guidebook for wetland restoration, planning and implementation. Publication 93-17. 110 pp.
plus appendices.
Golder Associates, Inc. 1992. Level 11 environmental assessment, south part of parcel 13, Glacier Park
Company. Prepared for the City of Renton. Redmond, Washington.
Hart Crowser, Inc. 1991a. Preliminary environmental assessment GPC property sequence no. 968,
parcels 13 and 14, Renton, Washington. Prepared for Mark Miller Consultants, Inc. Seattle,
Washington.
Hart Crowser, Inc. 1991b. Preliminary surface water and sediment quality assessment; Springbrook
Creek - Orillia Industrial Park, Renton, Washington. Prepared for Mark Miller Consultants, Inc.
Seattle, Washington.
Kennedy/Jenks/Chilton Consulting Engineers. 1989. Preliminary environmental assessment Orillia
Corporate Park property (Sequence 850), Renton, Washington. Prepared for Glacier Park
Company. Federal Way, Washington.
Parametrix, Inc. 2002. Mitigation Banking Program. Prepared for the City of Renton by Parametrix, Inc.
Kirkland, Washington
Snyder, D.E., P.S., Gale and R.F. Pringle, 1973. Soil survey of King County area, Washington. Prepared
by the U.S. Department of Agriculture Soil Conservation Service in cooperation with Washington
Agricultural Experiment Station. Washington, D.C. 100 pp. plus maps.
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Category 1 Wetland - Category 1 wetlands are very high quality wetlands, greater than 2,200 sq. ft, which
meet one or more of the following criteria:
a. The presence of species listed by federal or state government as endangered or threatened, or the
presence of essential habitat for those species;
b. Wetlands having 40 to 60 percent permanent open water (in dispersed patches or otherwise) with two
or more vegetation classes;
c. Wetlands equal to or greater than ten acres in size and having three or more vegetation classes, one
of which is open water,
d. The presence of plant associations of infrequent occurrence, or at the geographic limits of their
occurrence; or
e. Wetlands assigned the Unique/Outstanding #1 rating in the current King County Wetlands Inventory
1991 or as thereafter amended (City of Renton 2000).
Category 2 Wetland - High quality wetlands greater than 2,200 sq. ft, which meet one or more of the
following criteria:
a. Wetlands greater than 2,200 sq. ft that are not Category 1 or 3 wetlands;
b. Wetlands that have heron rookeries or raptor nesting trees, but are not Category 1 wetlands;
c. Wetlands of any size located at the headwaters of a watercourse, but are not Category 1 wetlands;
d. Wetlands assigned the Significant #2 rating in the current King County Wetlands Inventory 1991 or
as thereafter amended;
e. Wetlands having minimum existing evidence of human related physical alteration such as diking,
ditching, and channelization (City of Renton 2000);
Category 3 Wetland - Lower quality wetlands greater than 5,000 sq. ft, which meet one or more of the
following criteria:
a. Wetlands that are severely disturbed. Severely disturbed wetlands are wetlands that meet the
following criteria:
(1) Are characterized by hydrologic isolation, human -related hydrologic alterations such as diking,
ditching, channelization, an/or outlet modification; and
(2) Have soil alterations such as the presence of fill, soil removal, and/or compaction of soils; and
(3) May have altered vegetation.
b. Wetlands that are newly emerging. Newly emerging wetlands are:
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(1) Wetlands occurring on top of fill materials; and
(2) Characterized by emergent vegetation, low plant species richness, and used minimally by
wildlife. These wetlands are generally found in the areas such as the Green River Valley and
Black River Drainage Basin (City of Renton 2000).
Category II Wetlands - These wetlands: (1) provide habitat for very sensitive or important wildlife or plant;
(2) are either difficult to replace; or (3) provide very high functions, particularly for wildlife habitat (Ecology
1993).
Category III Wetlands - These wetlands are important for a variety of wildlife species and occur more
commonly than either Category 1 or 2 wetlands. Generally, these wetlands are smaller, less diverse, and/or
more isolated in the landscape than Category II wetlands (Ecology 1993).
Compensatory Wetland Mitigation - The process of creating, restoring, or enhancing wetlands to offset
losses to wetland impacts associated with development activities.
Ecosystem - A community of living organisms interacting with one another and with their physical
environment, such as a rain forest, pond, or estuary. An ecosystem is a single complex system and/or as the
sum of many interconnected ecosystems such as rivers, wetlands, and bays.
Emergent Wetland - An emergent wetland is an area of the wetland where non -woody vegetation cover at
least 30 percent of the ground.
Environmental Site Assessment - An environmental site assessment is an investigation of the presence or
likely presence of hazardous substances, including petroleum products, that may exist on a site due to past
on -site or off -site activities.
Exotic and Invasive Vegetation - Native and non-native species of plants which can form monocultures in
wetlands.
Floodplain - An area adjacent to a lake, stream, ocean, or other body of water lying outside of the ordinary
banks of the water body and periodically inundated by flood flows.
Forested Wetlands - Woody vegetation that provides a canopy over the wetland that is at least 20 ft tall and
50 years old for deciduous trees and 80 years old for evergreens.
Groundwater Recharge - The movement of surface water through an unsaturated zone of soil or rock into a
groundwater body.
Habitat Structure - The physical complexity within each wetland class.
Hydric Soil - A soil that is saturated, flooded, or ponded long enough during the growing season to
periodically develop anaerobic conditions.
Horizon - A distinct layer of soil, more or less parallel with the soil surface, having similar properties such as
color, texture, and permeability. The soil profile is subdivided into the following major horizons: (1) A -
horizon - characterized by an accumulation of organic material, (2) B-horizon - characterized by relative
accumulation of clay, iron, organic matter, or aluminum; and (3) the C-horizon - the undisturbed and
unaltered parent material.
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Mitigation Banking — Sites which may be used for restoration, creation, and/or mitigation of wetland
alternatives from a different piece of property than the property to be altered within the same drainage basin.
Performance Bond - Usually a financial payment made by project proponent to a local, state, or federal
agency. Bonding holds a permitter accountable for implementing the mitigation, monitoring, and
contingency plans.
Performance Standards - Measurable values of specific variables that establish when mitigation objectives
have been met. Performance standards may include values for variables such as dissolved oxygen, nutrient
levels in water, survival rate of planted vegetation, species diversity, water flows, water depths, and wetland
size.
Shrub Wetland - A shrub wetland is any area of vegetated wetland where woody vegetation less than 20 ft.
tall comprises at least 30 percent of the areal cover.
Species Diversity - The number of different plant species within each vegetated wetland class that cover at
least 5 percent of the ground within the area covered by that class.
Wetland - Wetlands are those lands transitional between terrestrial and aquatic systems that are inundated
or saturated by ground or surface water at a frequency and duration sufficient to support and, under
normal circumstances, do support prevalence of vegetation typically adapted for life in saturated soil
conditions (City of Renton 2000).
Wetland Buffer - Wetland buffers are designated areas adjacent to a regulated wetland which protect the
wetland from surrounding activities and protect adjacent properties from changes in the location of the
wetland edge (City of Renton 2000).
Wetland Classes - The types of vegetation in wetlands. Emergent, shrub, and forested wetlands are
examples of wetland classes.
Wetland Classification - The process of identifying and classifying wetlands.
Wetland Delineation - A determination that a water body or wetland is subject to interstate commerce,
and therefore is a water of the United States.
Wetland Functions - Wetland functions are the ecological functions that wetlands perform. Wetland
functions include providing flood control, water quality protection shoreline stabilization, contributions to
groundwater and stream flows, wildlife and fisheries habitat, and aesthetic, recreational, and education
opportunities.
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