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HomeMy WebLinkAboutSWP272884(10) R Wetland Mitigation Concepts Report, Houser Way Relocation Project- DRAFT WETLAND MITIGATION CONCEPTS REPORT HOUSER WAY RELOCATION PROJECT RENTON, WASHINGTON prepared for: The City of Renton Public Works Department Renton, Washington prepared by: Adolfson Associates, Inc. 5309 Shilshole Avenue NW Seattle, Washington April 1994 Wetland Mitigation Concepts Report, Houser Way Relocation Project - DRAFT • TABLE OF CONTENTS TABLE OF CONTENTS ...................................................................... i EXECUTIVESUMMARY .................................................................. . INTRODUCTION .............................................................................. 1 PROJECTDESCRIPTION ....................................................................1 SENSITIVEAREAS ...........................................................................3 Wetland Functions and Values ....................................................... Wetland Classification ................................................................. Wildlife/Habitat.........................................................................6 REGULATORY REQUIREMENTS .........................................................6 FederalRegulations ....................................................................6 StateRegulations .......................................................................7 LocalRegulations ......................................................................7 IMPACTS ........................................................................................9 MITIGATION CONCEPTS ...................................................................9 Mitigation Requirements ..............................................................9 Goals and Objectives...................................................................9 Conceptual Site Plan ...................................................................11 Clearing and Erosion Control.........................................................11 PlantPalette.............................................................................12 MAINTENANCE...............................................................................12 MONITORING AND REPORTING.........................................................13 SUCCESS CRITERIA..........................................................................13 CONTINGENCY PLAN.......................................................................14 FINAL MITIGATION PLAN.................................................................14 REFERENCES ..................................................................................15 04/13/94 i Wetland Mitigation Concepts Report, Houser Way Relocation Project - DRAFT EXECUTIVE SUMMARY At the request of ENTRANCO, consultants to the City of Renton (City), ADOLFSON ASSOCIATES, INC. (AAI) prepared a Wetland Mitigation Concepts report for the Houser Way site, located in Renton, Washington. The report addresses mitigation goals, maintenance and monitoring of the mitigation elements, success criteria, and a contingency plan. The project site is located at the toe of the steeply sloping, wooded western embankment of Interstate 405 (I-405). It extends from North 8th Street south to Sunset Boulevard and lies between the toe of the I-405 embankment and the Burlington Northern Railroad (BNR) line. Within the project area, a vegetated drainage channel and adjacent wetland is located at the bottom of the steep slope of the western embankment of I-405. The wetland is a mixed palustrine forested/scrub-shrub/emergent wetland characterized by a forest canopy layer dominated by red alder, black cottonwood, and western red cedar. The scrub-shrub and ground cover strata are dominated by red alder saplings, salmonberry, spiraea, and common horsetail. Upland vegetation in the general area consists of Douglas-fir, silver fir, and western hemlock. Scrub-shrub and ground cover strata include blackberry, sword fern, and Scot's broom. Impacts to the wetland will be primarily due to construction activities. These will include: roadway excavation, development of embankments and drainage systems, paving, construction of a wetpond for surface water management, and development of a wetland mitigation area. The open drainage channel will be filled, and the wetland adjacent to the drainage channel will be excavated during construction activities. The wetland soils within the drainage channel will be stockpiled for use in the mitigation wetland, as applicable. The goal of the mitigation plan will be to maintain or improve the functions and values which are presently provided by the wetland in this area, primarily storm water control and wildlife habitat. 04/13/94 ii Wetland Mitigation Concepts Report, Houser Way Relocation Project - DRAFT " INTRODUCTION At the request of ENTRANCO, consultants to the City of Renton (City), ADOLFSON ASSOCIATES, INC. (AAI) has prepared this technical report for the Houser Way site, located in Renton, Washington. The report is being completed as part of the Houser Way Relocation Project: the proposed construction of an extension of Houser Way from North 8th Street south to a connection with Sunset Boulevard. The boundaries of the study area were established on an aerial photograph supplied by Entranco and located in the field according to the aerial photograph. The first phase of the Scope of Work for this project included a wetlands determination, delineation, rating, a qualitative functional value assessment, and a brief discussion of regulatory implications and permitting considerations. These elements have been summarized in the report Houser Way Wetlands Study (Adolfson Associates, Inc. 1993). Phase two of the Scope of Work includes an analysis of potential wetlands impacts and the development of a mitigation plan. These elements are presented in this report. PROJECT DESCRIPTION The Houser Way Relocation Project site is located at the toe of the steeply sloping, wooded western embankment of Interstate 405 (I-405) in the City of Renton, in King County, Washington (Section 8, Township 23 North, Range 5 East). It extends from North 8th Street south to Sunset Boulevard and lies between the toe of the I-405 embankment and the Burlington Northern Railroad (BNR) line (Figure 1). The project is designed to alleviate the traffic congestion on North Renton neighborhood streets and arterials, mainly on North 3rd Street, North 4th Street, and Park Avenue North. The new roadway will provide a more convenient access for Boeing and PACCAR employees to neighboring highways such as I-405, SR 900, SR 169, and SR 167. The new Houser Way will be a frontage road to I-405 lying between and paralleling I- 405 and the Burlington Northern Railroad (BNR) railroad tracks. The roadway will extend from North 8th Street south to Sunset Boulevard just north of North 3rd Street. At its southern end, the new roadway will connect to Sunset Boulevard through an interchange and will require an undercrossing structure under the I-405 southbound off- ramp and Sunset Boulevard. At its northern end, the roadway will connect to the existing Houser Way and North 8th Street through a tee intersection. The total length of the project is approximately 2,600 feet. The roadway will be a two- way, two-lane street with a 14-foot-wide lane in each direction. A six-foot sidewalk on the west side will diverge from the roadway just before the undercrossing. The sidewalk will then become grade-separated and run along the west side of the undercrossing and Sunset Boulevard, finally merging with the existing sidewalk on 04/13/94 1 z3 o� Z3 AY ItuIUUY ju , LL AY AY M dN (y iv z ►I>jua3a`v �� �� � U I I 1113U83UY x II hY r II13083UYS —Nu Aisiilwn 'C) CL "'Jol � E Q IU`11 nl �� s✓ x pi nF pw"iuv! U 11:1 AY 113U8Y9 N HY.d 113UHV9 � 11 AV MUYJ J n'Y �iiv� it nv— )r6j— l _ �\� u�AY AIIJJ it"hl— —Tl1 D / ��� •p �� I I!M ,. AY 5 11lA u L — _ _ _ _ ii nv�snr (�/U hY snvl I Inl U C � -_ _ u=I 11 AY (IYUu I •� CJ"E ° ,, IUCNI hY I U I gd l l l l l l l n- x -��g s^Y " 1 ARC .5 5 A Ii 0 z Wetland Mitigation Concepts Report, Houser Way Relocation Project - DRAFT, Sunset Boulevard north of North 3rd Street. A three-foot curb on the east side of the roadway will begin just south of North 8th Street and terminate just north of the undercrossing. The steepness of the I-405 embankment and the drainage conditions in the project area will require construction of a retaining wall just south of North 8th Street. Work will include: paving, curbs, gutters, sidewalks, structural walls, an undercrossing structure, storm drainage, water quality treatment, channelization, signalization, and environmental assessment. This report summarizes the conceptual approach to the compensatory wetland mitigation which will be required for this project. SENSITIVE AREAS Within the project area, a vegetated drainage channel is located at the bottom of the steep slope of the western embankment of I-405. The channel conveys surface and storm water flows north approximately 1,600 feet north along the toe of the embankment to a 42-inch concrete storm drain along North 8th Street. The flows then travel 900 feet west in this system to a 72-inch concrete storm drain along Garden Avenue North to Park Avenue North. At the south side of Park Avenue North, the flows join other storm flows and are conveyed through Gene Coulon Park in a low gradient, open channel locally known as Johns Creek. The flows then discharge to Lake Washington. One wetland, comprising 0.98 acres, was identified on the project site within and adjacent to the drainage channel (Figure 2). The wetland is a mixed palustrine forested/scrub-shrub/emergent wetland characterized by a forest canopy layer dominated by red alder, black cottonwood, and western red cedar. The scrub-shrub and ground cover strata are dominated by red alder saplings, salmonberry, spiraea, and common horsetail. Upland vegetation in the general area consists of Douglas-fir, silver fir, and western hemlock. Scrub-shrub and ground cover strata include blackberry, sword fern, and Scot's broom. Wetland Functions and Values The wetland was evaluated according to the methodology developed by the Army Corps of Engineers (Corps) (Reppert et al., 1979). It was given a MODERATE rating for water quality improvement, as the hydrophytic vegetation within and adjacent to the channel provides runoff retention and water purification functions. The wetland received a LOW-to-MODERATE rating for storm and flood water control and hydrologic support due to its small size and the low degree of woody cover. Although the wetland rated LOW for biological support due to its small size and lack of unique species, its moderate plant diversity and ability to support water dependent species, such as waterfowl, earned it a MODERATE rating. These ratings are provided in Table 1. 04/13/94 3 WETLANO A 42.656 S.F./ 0.96 ACRES -rrr ••'•. Lr •'� WETLAND A DP OS WETLAND A •• • • • :,� H04 �7 �34p • ..- - OPI • `` j ` CITY OF RENTON w • a wa ta• NOUSER WAY RELOCATION •n ro nw<..a w WMA"O LOCATION fi N T fl A N C 0 uwcml uiw� ur•ru „• Wetland Location Figure 2 Approximate Scale 0 1 : 200 Houocr Way Relocation project la�� ADOLFSON ASSOCIATES, INC. Table 1. Functional Value Assessment for Hauser Way - Wetland A CRITERIA FUNCTIONAL VALUES Low Rating Moderate Rating High Ratio Water Quality 1) intermittently 1) associated with 1) associated with Improvement flooded wetland lake estuary or perennial 2) < 50% 2) 50-80% stream or river herbaceous cover herbaceous cover 2) > 80% 3) size < 10 acres 3) size 10-100 acres herbaceous cover 4) no proximity to 4)downstream from 3) size > 100 acres pollutants/ not nonpoint pollutants 4) downstream from downstream from 5) retains 25-50% municipal point industrial point overland runoff discharges discharges 5) retains > 50% 5) retains < 25% overland runoff overland runoff Storm and Flood 1) size < 5 acres 1) size 5-10 acres 1) size > 10 acres Water Control 2) directly upstream 2) directly upstream 2) directly upstream from remote areas from rural areas from urban & 3) < 10% woody 3) 10-30% woody developable areas cover cover 3) > 30% woody 4) isolated/ no cover cumulative effects Hydrologic 1) size < 5 acres 1) size 5-10 acres 1) size > 10 acres Support 2) hydrologically 2) seasonally 2) permanent (Streamflow isolated flooded/ associated inundation/ Maintenance) 3) temporarily with riverine or associated with saturated or lacustrine systems estuary inundated; low 3) moderate flooding 3) high flooding flooding frequency frequency frequency 4) located adjacent to 4) located adjacent to an adjacent wetland open water Biological Support 1) vegetation lacking 1) shrub/forested 1) marsh [except mudflats] swamp 2) intertidal marsh/ 2) isolated systems/ 2) upper tidal marsh/ associated with wetland associated associated with permanent stream or with ephemeral intermittent streams river streams 3) two habitat types 3) three or more 3) one habitat type 4) moderate plant habitat types 4) low plant diversity diversity 4) high plant 5) no or few habitat 5) several habitat diversity features features 5) many habitat 6) no unique species 6) unique species features 7) no water- potential 6) unique species dependent species 7) water-dependent present 8) small size species potential 7) water-dependent 8) medium size species present 8) large size Wetland Mitigation Concepts Report, Houser Way Relocation Project - DRAFT Following implementation of the wetland mitigation concepts discussed in this report, it is anticipated that there will be a small net increase of wetland functions and values in the project area. Wetland Classification The City of Renton classifies wetlands in its Wetlands Management Ordinance (No. 4346) based upon area, the presence of salmonids, the number of vegetation classes, the presence of permanent open water, and the presence of endangered or threatened species and/or habitat(s). The wetland does not contain permanent open water and is subject to continued disturbance for maintenance as a drainage channel. According to the Ordinance, the wetland merits a Category 3 - Lower Quality Wetland rating due to the degree of disturbance it receives, its low-to-moderate wetland functions ratings, and its low usage by wildlife. Wildlife/Habitat A female mallard was the only wildlife identified within the project area during field observations. A few unidentified songbirds were heard and seen, and coyote sign was observed near the streambed. No other wildlife presence was detected. A small forested component at the toe of the slope from I-405 adjacent to the wetland provides some habitat for wildlife; however, its habitat function is not intrinsic to the wetland. This area is the same forested community found along the toe of the I-405 embankment where no wetlands exist. This area is not expected to receive much use by wildlife due to its position between a major highway on one side and railroad tracks and an industrial area on the other. No endangered, threatened, or sensitive species of plant or animal were observed at the site during the field observations. This observation has been subsequently confirmed by a search of the Priority Habitats and Species data base of the Washington Department of Wildlife and the Natural Heritage Program data base of the Washington Department of Natural Resources (WDNR, 1993). REGULATORY REQUHUAEENTS Federal Regulations All federal actions or projects receiving federal funding are subject to the 1969 National Environmental Policy Act (NEPA). Section 401 of the Clean Water Act (CWA) mandates that federally permitted activities in wetlands comply with the CWA and state water quality standards. The principal applicable federal law regulating activities in or near wetlands is Section 404 of the CWA. Under Section 404 of the CWA, the U.S. Army Corps of Engineers (Corps) has been given the responsibility 04/13/94 6 Wedand Mitigation Concepts Report, Houser Way Relocation Project - DRAFT and authority to regulate the discharge of dredged or fill materials into waters and adjacent wetlands of the United States (Federal Register, 1986). Section 404 permitting is most commonly applied to freshwater wetlands. Two kinds of permits are issued by the Corps: General and Individual. General Permits (also known as Nationwide Permits, or NWPs) cover proposals that would have minimal adverse impacts on the environment. The NWP for wetland alterations applicable to the Houser Way Project is NWP 26. This NWP specifically addresses wetlands which are (1) above the headwaters of a river or stream (that point in the watercourse at which the mean annual discharge is less than five cubic feet per second) or (2) hydrologically isolated. Such permits apply to fills and other impacts of less than one acre. Proposed impacts from 0.99 acre to two acres also require a Water Quality Certification under Section 401 of the CWA from the Department of Ecology (see below). State Regulations The Washington State Department of Ecology (Ecology) becomes involved through a requirement for Coastal Zone Management Consistency under the authority of the U.S. Coastal Zone Management Act (16 U.S.C. 1451 et. seq.) and its regulations (15 CFR Parts 923-930). In this process, Ecology reviews projects for consistency with state requirements, including Shorelines Permits. If a project is consistent, Ecology issues certification. Note that the local jurisdiction typically administers Shoreline Management Plans. In addition to Coastal Zone consistency, Ecology issues Water Quality Certification (Federal Clean Water Act Sec. 401; Chapter 173-225 WAC) for activities which may result in discharges into surface waters. All actions which may impact the natural or built environment are subject to the State Environmental Policy Act (SEPA) of 1971 (with new implementation rules adopted in 1984, Chapter 197-11 WAC) and, in Western Washington, to the Puget Sound Water Quality Act (Chapter 90.70 RCW). The State Hydraulic Code requires Hydraulic Project Approval for projects below the ordinary high water mark, and the Floodplain Management Program has jurisdiction over construction in floodways and floodplains that may affect flood elevations and/or flood protection. Local Regulations Permits from the cities with jurisdiction over the project area must be granted before the commencement of construction in any wetland or wetland buffer. Most cities require a wetland delineation and preparation of a wetland mitigation plan for all wetlands affected by the project. The final approval of both the wetland delineation and the mitigation plan is granted by the city in question. 04/13/94 7 Wetland Mitigation Concepts Report, Houser Way Relocation Project - DRAFT The City of Renton regulates wetlands under its Wetlands Management Ordinance (Title IV, Chapter 32, ##4346). Under the Ordinance, wetlands may be assigned one of three ratings, as follows: "1. Very HiPh Quality Wetlands- Category I wetlands are 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% 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. 2. High Quality Wetlands- Category 2 wetlands are 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, channelization. 3. _Lower Quality Wetlands - Category 3 wetlands are wetlands greater than 45,000 sq. ft. which meet one or more of the following criteria: a. Wetlands that are severely disturbed. Severely disturbed wetlands are wetlands which meet the following criteria: (1) Are characterized by hydrologic isolation, human-related hydrologic alterations such as diking, ditching, channelization, and/or outlet modification; and (2) Have soils 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: (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. c. All other wetlands not classified as Category 1 or 2 such as smaller, high quality wetlands." The Ordinance also establishes minimum buffers of 100, 50, and 25 feet for Category 1, 2, and 3 wetlands, respectively. Alterations to wetlands or their required buffers are allowed by the City only under specified conditions. 04/13/94 8 Wetland Mitigation Concepts Report, Houser Way Relocation Project - DRAFT The City recognizes that application of the Ordinance may deny all reasonable use of a given property. If such circumstances are demonstrated, development may be allowed which is consistent with the general purposes of the Ordinance and the public interest. Environmental impacts, including impacts to wetlands, are reviewed by the Environmental Review Committee of the City's Development Services Division. A wetland development permit is required prior to any development or alteration of a property which contains wetlands. Ili TACTS Construction activities will include: roadway excavation, development of embankments and drainage systems, paving, construction of a wetpond for surface water management, and development of a wetland mitigation area. The open drainage channel will be filled, and the wetland adjacent to the drainage channel will be excavated during construction activities. The wetland soils within the drainage channel will be stockpiled for use in the mitigation wetland, as applicable. NMGATION CONCEPTS Mitigation Requirements According to the City of Renton's Wetlands Management Ordinance, mitigation for impacts to wetlands must be considered in the following order: (1) avoid disturbance to wetlands and/or buffers; (2) minimize impacts to wetlands and/or buffers; (3) compensate for any wetland or buffer impacts; (4) restore any wetlands or buffers impacted; and (5) create new wetlands and buffers to replace those which were lost. The City maintains a policy of balancing community desires for economic development, public health, safety, and welfare with support for the concept of no net loss of wetland acreage, functions, and values. The City encourages protection of high value wetlands, restoration of disturbed or low quality wetlands, and creation of new wetlands to offset unavoidable impacts or losses. For this project, the design team considered all practical efforts to avoid and minimize potential impacts to the wetland, including modification of the preferred alignment, restricting specific construction activities during certain times of the year, and limiting clearing and grubbing only to those areas necessary to construct the project. Avoidance of wetlands, however, will not be possible in this case due to the location of the wetland in the only practicable alignment path of the new roadway. Accordingly, mitigation measures for this project have relied heavily on wetland creation as compensation for impacts to wetlands. Goals and Objectives The goal of the mitigation plan will be to maintain or improve the functions and values which are presently provided by the wetland in this area, which include: 04/13/94 9 Wetland Mitigation Concepts Report, Houser Way Relocation Project - DRAFT • Flood storage/desynchronization • Water quality improvement • Wildlife habitat Mitigation will be accomplished in several ways. The project is situated at a point where hillside drainage reaches the valley floor. The project site, as well as other areas downstream of the project, have flooded in the past during large storm events. The functions of flood storage/desynchronization and water quality improvement will be provided through construction of a grass-lined swale/ditch approximately 1,600 feet long on the west side of the roadway to convey both on-site flows and the regional flows entering the south end of the site. These flows will be conveyed to a wetpond constructed on the east side of the North 8th Street/Houser Way intersection. Additional flood storage will be provided in a created wetland adjacent to the wetpond on the north side which will be able to receive overflows from the wetpond during severe storm.events. Under normal circumstances, however, the wetland will not receive flows from the wetpond. The wetpond will discharge at Houser Way and North 8th Street to the existing storm drain system. Wetland and wildlife habitat will be provided by creating approximately 11,340 square feet of palustrine wetland in an existing upland area at the intersection of North 8th Street and Houser Way. Additional habitat will also be provided for approximately 5,400 square feet of the wetpond area. The created wetland will contain a mosaic of several habitat types, including emergent vegetation, shrubs, and trees. Shrubs and trees will be planted on the margins of the wetpond. Shrubs and trees will provide shade for both the wetland and the wetpond and help to moderate water temperature. One of the objectives of this plan is to create wetland and wildlife habitat on-site. Not only will this avoid habitat fragmentation, but this strategy will also render maintenance and monitoring programs more efficient and cost effective. Because the area for wetland and wetpond creation is limited, the full 25 feet of buffer for the wetland will not be available. However, the wetland will still be effectively buffered from intrusion and disturbance by the following elements. In addition to the wetland plantings, native vegetation will be planted between the created wetland and the roadway to buffer the area from human and domestic animal intrusion. The buffer will be planted with native upland tree and shrub species such as hawthorn, currant, and rose, which will discourage entry into the wetland. In addition, the east side of the created wetland will be buffered by the slope of the I-405 embankment. These elements were discussed with the City of Renton Planning Department staff member assigned to the project during a preliminary review of the wetland mitigation concepts. The buffer concepts were considered to provide adequate protection for the wetland and were approved. 04/13/94 10 Wetland Mitigation Concepts Report, Houser Way Relocation Project - DRAFT The mitigation concepts are consistent with the spirit of the City's intent for wetlands management, in particular, "the City encourages land development projects which seek to improve the hydrologic and wildlife habitat functions of low value wetlands (4-32- 1B. Policy and Purpose). Conceptual Site Plan The criteria for selecting a mitigation site included the following considerations: (1) a preference for sites located within the same drainage basin; and (2) sites located within the project right-of-way. Due to the nature of the steep topography and existing land uses within the Fast Lake Washington drainage basin, the potential for suitable wetland mitigation sites is extremely limited. Several sites were examined within Gene Coulon Park, including areas adjacent to Johns Creek and the Trestle Marsh. However, mitigation at these sites would primarily involve enhancement of existing wetland areas, and the City does not recognize enhancement as compensatory mitigation. The areas within the project site will be designed to provide the same, if not greater, functions and values as the existing wetland/drainage system. The wetland and wetpond site is a grassy, wooded upland area located at the north end of the project area, between the end of North 8th Street and the toe of the I-405 embankment. It is of primary importance that wetland hydrologic conditions be provided in the created wetland. This will be accomplished by excavating a basin at the new wetland site and allowing seeps and springs at the base of the I-405 embankment to provide a water supply to the wetland. The location of the mitigation site is also important. One of the goals of this plan to avoid habitat fragmentation; accordingly, the created wetland will be situated so that it forms a continuum with adjacent and nearby natural areas along the toe of the I-405 embankment. Clearing and Erosion Control During construction, all machinery, materials, stockpiled soils, and construction activity will be confined to the areas allotted and approved by the City for construction related operations. Areas used to stockpile soils will be protected and covered to prevent drying and erosion. An erosion control plan will be implemented at the construction site which will employ standard erosion control practices required by the City. The mitigation wetland and buffer boundaries will be clearly marked with highly visible markers such as bright orange barrier fencing so that unauthorized construction activities do not occur in these areas. Straw bales and silt fences will be placed along the construction limits during and immediately after construction. 04/13/94 11 Wetland Mitigation Concepts Report, Houser Way Relocation Project - DRAFT Plant Palette Shrubs and trees will be planted in groups designed to duplicate and supplement the plant communities in the existing wetland/drainage channel. Planting will be done by hand or using small mechanized equipment that will not compact soils. Within the mitigated wetland, a variety of native tree, shrub, and emergent species will be planted at appropriate elevations (with respect to seasonal water levels). Native tree and shrub species will also be planted on the margins of the wetpond. These species may include the following: Common Name Taxonomic Name Trees: western hemlock Tsuga heterophylla black cottonwood Populus balsamifera Shrubs: willow Salix spp. salmonberry Rubus spectabilis Herbs: great bulrush Scirpus validus small-fruited bulrush Scirpus microcarpus spike rush Eleocharis spp. daggerleaf rush Juncus ensifolius sedges Carex spp. Contractors will be required to obtain plant species commercially available from local sources and native to western Washington. If applicable, following excavation, the exposed surface of the created wetland will be lined with hydric soils excavated from the drainage channel. It is expected that the seed bank in these soils will supply additional plant species beginning in the first growing season. These volunteer plant species include water cress, cattails, horsetail, and red alder. They will contribute to the mosaic of habitat types planned for the new wetland. In addition to the wetland plantings, a strip of native vegetation will be planted between the mitigation wetland and the roadway to buffer the area from human and domestic animal intrusion. The buffer will be planted with native upland tree and shrub species which will discourage entry into the wetland, such as hawthorn, currant, and rose species. The area will also be hydroseeded with a standard erosion control mix. MAINTENANCE Maintenance of the mitigation site will begin after completion of construction and continue for three years. After acceptance of the initial planting, the construction contractor will be responsible for plant survival for a period of one year. After this 04/13/94 12 Wetland Mitigation Concepts Report, Houser Way Relocation Project - DRAFT ' period, maintenance will be performed by the City of Renton and would be confined to repairing vandalism, repairing erosion damage, minor revegetation, and noxious weed control. MONITORING AND REPORTING The progress of the mitigation project will be evaluated seasonally for a period of three years by qualified technical personnel, using wetland monitoring protocols developed for the site and approved by the City. Observations will be made during the monitoring period of growth patterns; any apparent plant stress, pest, or parasite infestation; the adequacy of the water supply; and any invasion or spread by noxious weed species. Monitoring of the revegetated areas will also assess the success of the establishment of the native species. The results of the monitoring program will be recorded in an annual report prepared for review by the City and other appropriate agencies. This report will be prepared in a quality and format consistent with published scientific literature so that information contained within the report may be used for future wetland mitigation projects. SUCCESS CRrITY IA The following criteria are proposed by which to evaluate the success of the mitigation measures: 1. Ninety-five percent plant survival rate after the first year, as guaranteed by the landscaping contractor. After the first year, a maximum of 20 percent mortality will be allowed. 2. Areal cover development according to the following: Emergent Species 80% cover after three years Shrub Species 1st year -20%-30% cover 2nd year - 30%-45% cover 3rd year - 45%-75% cover Tree Species 1 st year - 10%-20% cover 2nd year - 20%-30% cover 3rd year - >45% cover 04/13/94 13 Wetland Mitigation Concepts Report, Houser Way Relocation Project - DRAFT CONTINGENCY PLAN If the monitoring results indicate that success criteria are not being met, it may be necessary to implement the contingency plan. Careful attention to construction management is essential in ensuring that problems do not arise. Any plant species with a 30% or greater mortality rate after two growing seasons will be replaced with either the same or a more appropriate approved species. The landscaping contractor will guarantee 90 percent survivorship for one year following initial planting for losses due to defects in materials or workmanship. Dead plants will be replaced at no charge as part of the guarantee during the first year. Replacements made by a landscaper will be subject to the same conditions and will meet the same standards as specified for the original planting. FINAL MITIGATION PLAN/CONSTRUCTION DRAWINGS A final mitigation workplan for use by the mitigation contractor, including construction drawings and contract specifications for planting and maintenance of the mitigation area, will be prepared following acceptance of this Wetland Mitigation Concepts Report. 04/13/94 14 Wetland Mitigation Concepts Report, Houser Way Relocation Project - DRAFT REFERENCES Adolfson Associates, Inc. 1993. Houser Way Wetlands Study. Seattle, Washington. Entranco. 1993. Houser Way Relocation Project, Stage II Study. Bellevue, Washington. King County. 1990. Sensitive Areas Map Folio. Planning and Community Development Division, King County, Washington. King County. 1990. Wetlands Inventory, Volume 2 East. Environmental Division. Bellevue, Washington. City of Renton. 1986. City of Renton Comprehensive Plan Compendium. Renton, Washington. City of Renton. 1991. City of Renton Fish and Wildlife Habitat. Prepared by David Evans and Associates, Inc. Renton, Washington. City of Renton. 1992. Critical Areas Inventory, City of Renton Wetlands and Stream Corridors. Prepared by Jones & Stokes Associates in association with R.W. Beck and Associates. Bellevue, Washington. City of Renton. 1992. Critical Areas Maps. Long Range Planning, Planning/Building Public Works, Technical Services. Renton, Washington. City of Renton. 1992. Wetlands Management. Ordinance No. 4346. Title IV, Chapter 32, of Ordinance No. 4260 Code of General Ordinances of the City of Renton, Washington. Renton, Washington. Washington State Department of Natural Resources. Data base regarding endangered, threatened, and sensitive plants and high quality native plant communities and wetlands. Olympia, Washington. Washington State Department of Wildlife. 1993. Priority Habitat and Species and Nongame Systems, Mercer Island Quadrangle. Olympia, Washington. PERSONAL COMMUNICATIONS Fisher, Larry. Washington State Department of Fisheries, Regional Habitat Manager. Issaquah, Washington. October 27, 1993. 04/13/94 15