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2010-04-07 HEX# 10-002 Exhibit I
Draft Stream Mitigation Plan 1-5 - SR 161,/SR 18 Triangle Improvements Project Submitted to Washington State Department of Transportation February 2009 Submitted by BERGER/ABAM Engineers Inc. 720 Olive Way, Suite 1100 Seattle, Washington 98101 Job No. FAPWr4044064 PAGE-L-0 __�f� DRAFT STREAM MITIGATION PLAN 1-5 - SR 161/SR 18 TRIANGLE IMPROVEMENTS PROJECT WASHINGTON STATE DEPARTMENT OF TRANSPORTATION TABLE OF CONTENTS SECTION PAGE EXECUTIVESUMMARY ............................................... . .................................................1 1.0 INTRODUCTION AND BACKGROUND..............................................................................3 2.0 PROPOSED PROJECT......................................................................................................3 2.1 Tlmellne...........................................................................................................................5 2.2 Purpose and Need...........................................................................................................5 3.0 EXISTING CONDITIONS...................................................................................................5 3.1 Overview..........................................................................................................................5 3.2 Streams...........................................................................................................................8 3.3 Riparian Vegetation........................................................................................................15 4.0 STREAM AND RIPARIAN AREA IMPACTS ........ ........ ...... ...................... ,-....................... 19 4.1 Permanent Stream Impacts...........................................................................................19 4.2 Riparian Impacts............................................................................................................22 4.3 Stream Impact Summary ................................................................................................24 5.0 STREAM MITIGATION ACTIVITIES................................................................................24 5.1 Overview..........................................................................................................................24 5.2 Mitigation Approach.......................................................................................................25 5.3 Stormwater Quality and Quantity Retrofit .....................................................................25 5.4 Stream Relocation and Restoration.......................................„.....................................30 5.5 Riparian Habitat Creation/Enhancement.....................................................................33 5.6 Off -Channel Fish Habitat Creation.................................................................................37 5.7 Riparian Area Enhancements........................................................................................39 6.0 MITIGATION OBJECTIVES AND PERFORMANCE STANDARDS......................................41 6.1 Mitigation Goals..................................,.........................................................................Al 6.2 Mitigation Objectives.....................................................................................................41 6.3 Performance Measures and Success Standards..........................................................42 7.0 REFERENCES ...................................... ,................... ...... ...... ............... ............................ .43 LIST OF TABLES Table 1. Streams in the Project Area.........................................................................................10 Table2. Permanent Stream Channel Impacts...........................................................................19 Table 3. Permanent and Temporary Riparian Buffer Area Impacts (acres) .............................22 Table4. Impact and Mitigation Summary ..................................................................................25 TableS. Stormwater Treatment Summary .................................................................................29 Table 6. Comparison of Annual Pollutant Loads (Pounds per Year)........................................29 Table 7. Riparian Enhancement and Restoration Plant List....................................................35 Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 I-5 - SR 161/SR 18 Triangle Improvements Project February 2009 Washington State Department of Transportation g T Page i PAGE._. .OF•1- 1, LIST OF FIGURES Figure 1- Project Area Vicinity Map ......... ............... .......... -.....-............ ................................. 4 Figure 2 - Overview of In -Water Work ................................................. ..... ..-........ .....,...--.6 Figure 3 - Project Area Drainage Subbasins....... .............................. .......... .................. --.......7 Figure 4 — Observed Flow Data for Tributary 0016A................................................................13 Figure 5 — Existing Riparian Habitat Areas ............... ... .......................... ............. ........... .,..,.18 Figure6 — Stream Impacts.........................................................................................................20 Figure7 — Riparian Area Impacts ...................................... ........ ............................................ —.23 Figure 8— Stormwater Drainage Basin Map..............................................................................27 Figure 9 — Detention Pond Effect on Peak Flows ...................... ...................... — ..... ......... ....... 31 Figure 10 — Channel Realignment and Riparian Area Enhancement......................................32 Figure 11— Corrington Mitigation Site Conceptual Stream Mitigation Plan ..........................40 LIST OF PHOTOS Photo 1 Tributary 0016A In back of Costco. Culvert outlet from the southwest cloverleaf ramp of SR 18. The wading staff to the left of the culvert Is 6 feet tall. Photo 2 Typical riffle In Tributary 0016A. Photo 3 Tributary 0016A just downstream of the 1-5 culvert. Water flows slowly through the reed canarygrass. Photo 4 Inlet of Tributary 0016A culvert under i-& Photo 5 Tributary 0016A north of the SR 18/1-5 Interchange Photo 6 Looking at the Weyerhaeuser Corporate Headquarters building from the culvert outlet of Tributary 0016. This culvert extends all the way across this field and under the building to Weyerhaeuser Pond. Photo 7 Mud -filled pool at outlet of Tributary 0016 culvert under SR 18. The pool Is backwatered by an 18-Inch-high rock weir about 50 feet downstream. The rock dam Is outside of the SR 18 right-of-way. Photo 8 Typical mud -bottom gilds habitat on Tributary 0016 downstream of SR 18. Note house on right. Photo 9 Tributary 0016A south of the SR 18/1-5 Interchange. Note log weir and streambank stabilization with rock. Photo 10 Dry channel of Tributary 0016A In October 2005. Location of picture Is west side of I- 5 south of the SR 18/1-5 Interchange near the location of the proposed southbound offramps to SR 161 at South 356th Street. Photo 11 Dry channel of Tributary 0016A In October 2005. Photo taken where the existing stream channel will be filled and relocated to the west (left). Channel overgrown with reed canarygrass. Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 I-5 — SR 161/SR 18 Triangle Improvements Project February 2DG9 Washington State Department of Transportation EXHIBIT :1: Page ii PAGE 3 0E--�L.- EXECUTIVE SUMMARY Through the Interstate 5 (I-5) - State Route (SR)161/SR 18 Interchange Improvements Project (Triangle project), the Washington State Department of Transportation (WSDOT) proposes to replace two existing cloverleaf loop ramps with direct access flyovers and add new roadway lanes in high traffic areas. The proposed work will result in unavoidable impacts to a tributary to East Branch Hylebos Creek (Tributary 0016A) and to riparian areas associated with Tributary 0016A and East Branch Hylebos Creek (Tributary 0016). Direct impacts to Tributary 0016A will result from extending three existing culverts, placing a new culvert, and rerouting and abandoning a section of the existing stream channel to accommodate a new offramp from I-5 to SR 161 at South 356th Street. About 745 lineal feet of Tributary 0016A will be affected by these in -water construction activities. The project will not affect the stream channel of Tributary 0016 directly. Widening 1-5 with a new collector -distributor lane, new offramps, and new structures will encroach into riparian areas associated principally with Tributary 0016A. This widening will permanently affect an estimated 4.44 acres of Tributary 0016A riparian areas. An estimated 1.28 acres of riparian areas associated with Tributary 0016A will be temporarily disturbed and restored during construction. Construction of a stormwater pond south of SR 18 will encroach into Tributary 0016 riparian areas, permanently affecting 0.20 acre. A small amount of temporary disturbance to riparian areas associated with Tributary 0016 will result from constructing a retaining wall adjacent to the upstream end of the SR 18 culvert. The retaining wall is being constructed instead of a slope embankment in order to reduce stream and wetland impacts. This area will be restored during construction. The project will mitigate the stream and riparian area impacts by improving the quality and detention of runoff from existing impervious surfaces, removing existing culverts, and creating and restoring stream and riparian habitat within the project limits. The project will build detention and water quality treatment facilities for the 14.7 acres of new impervious surfaces it will create. In addition, it will provide water quality treatment and stormwater control facilities for 34.1 acres of existing 1-5 and SR 18 impervious surfaces. This added detention will help address the flashy flows characteristic of Tributary 0016A and provide a more regulated downstream discharge. The moderated flows and increased water quality treatment provided by the project's drainage facilities will reduce suspended solids and channel erosion and improve water quality in downstream reaches of Tributary 0016 where higher quality aquatic habitat exists. To mitigate filling and abandoning approximately 495 feet of the existing channel of Tributary 0016A to accommodate widening, the project will realign the channel, creating approximately 515 feet of seasonal stream channel habitat and associated riparian area. Draft Stream Mitigation Plan T BERGER/ABAM, FAPWT-04-064 I-5 — SR 161/SR 18 Triangle Improvements Project EACH ! B IT � February 2009 Washington State Department of Transportation Page 1 PAGE�_0F Mitigation for existing fish barriers on Tributary 0016A within the project area will consist of enhancement activities at WSDOT's Comngton mitigation site in the West Branch of Hylebos Creek subbasin, on South 364th Street. A 430-linear-foot side channel (0.05 acre) will be constructed at the site to provide off -channel rearing habitat. This new channel will connect to the existing pond (0.14 acre) at the site, and will meander to the south and west, where it will drain into Tributary 0015. The groundwater baseflow entering the pond will supply a constant source of clean, cool water for the creek that will help provide high quality habitat for fish species. This mitigation will provide more valuable habitat for resident and anadromous fish species than that provided through the removal of existing fish passage barriers on Tributary 0016A. In addition, the project will remove the loop ramp and two existing culverts in the northwest loop of the SR 18/1-5 interchange. This will allow the daylighting and restoration of approximately 250 feet of Tributary 0016A channel and its associated riparian area. Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 1-5 — SR 161/SR 18 Triangle Improvements Project February 2009 Washington State Department of Transportation EXHIBIT Page 2 1.0 INTRODUCTION AND BACKGROUND The Washington State Department of Transportation (WSDOT) proposes to complete a series of road improvement projects in Federal Way, Washington, through a project known as the I-5 — SR 161/SR 18 Interchange Improvements Project, also known as the Triangle project (Figure 1). The project will replace two existing cloverleaf loop ramps with direct access flyovers and add new roadway lanes in high traffic areas. The proposed work will result in unavoidable impacts, principally to Hylebos Creek Tributary 0016A and associated riparian areas. The proposed impacts are regulated by the US Army Corps of Engineers, the Washington State Department of Ecology, Washington State Department of Fish and Wildlife (WDFW), and the City of Federal Way (City). Prior approval from these agencies will be necessary before clearing and grading activities that would impact these streams and their riparian areas can commence. WSDOT proposes to use several methods to complete stream and riparian area mitigation for these planned impacts. This conceptual mitigation plan summarizes information about the proposed project and its projected impacts, and provides a conceptual -level outline of the proposed mitigation measures. 2.0 PROPOSED PROJECT The Triangle project will result in the construction of road modifications that will increase driver safety, reduce existing and projected traffic congestion, and increase freight and vehicle mobility. During the design process, a number of different build alternatives were developed and analyzed in a two-phase WSDOT screening process. The project team selected the current build alternative for its top scores in minimizing environmental impacts, as well as in four of the six categories reviewed. The principal features of the project are ■ Constructing a collector -distributor (CD) road between southbound I-5/westbound SR 18 to SR 161 via the construction of new ramps at South 356th and South 359th streets. ■ Constructing a new two-lane flyover to replace the existing single -lane northwest loop ramp for westbound SR 18 to southbound I-5 traffic. ■ Replacing the existing southeast loop ramp with a new flyover ramp to allow direct access for eastbound SR 18/South 348th Street to northbound I-5 traffic. ■ Reconfiguring the South 348th Street/SR 161 intersection to reduce left -turn movements and decrease congestion. ■ Constructing auxiliary lanes along I-5 between the area south of the South 336th Street bridge and the exit/entrance to the weigh station/rest area. Draft Stream Nlittgabon Plan I-5 — SR 161/SR 18 Triangle Improvements Project Washington State Department of Transportation BFRGMAB", FAPWT-O"" February 2009 EXH113JT � Page PAGE OFF_ Legend Project Limits Mitigation Site Figure 1 Project Area Vicinity Map Draft Stream Mitigation Plan 1-5/SR 161 /SR1 8 Triangle Improvements e0 loon 2000FeetDraft I i t i I Figure 2 provides a large-scale overview of the improvements proposed. In addition to these activities, the project includes the construction of stormwater treatment infrastructure and retaining walls and the replacement and extension of culverts as necessary. 2.1 Timeline Construction will occur in two phases, with the first phase beginning during spring 2010 and finishing at the end of 2013. The first phase of construction would address the weaving pattern of the northbound I-5/westbound SR 18 loop ramp and reduce congestion and improve safety at the South 348th Street/SR 161 intersection by providing a direct access ramp between I-5 and SR 18 to SR 161. The second phase of the project would complete all the remaining improvements of the build alternative. 2.2 Purpose and Need The purpose of the proposed project is to address safety concerns, reduce traffic congestion, and increase vehicle and freight mobility. Increased traffic volumes, combined with explosive land use, resulting in part from statewide land use regulations and zoning requirements, have caused increasing congestion and safety problems within the project area. Current traffic counts exceed capacity on SR 161 and are expected to continue to rise as south King County and north Pierce County grow. These facts, combined with the safety problems stemming from loop ramps that do not meet current design guidelines, have resulted in congestion and higher accident numbers. 3.0 EXISTING CONDITIONS 3.1 Overview The Triangle project area is located within the City of Federal Way and is bounded roughly to the north by South 336th Street, to the east by Weyerhaeuser Way, to the south by SR 161, and to the west by Enchanted Parkway South The entire project area is located within the West Branch and East Branch subbasins of Hylebos Creek (Figure 3). Land uses within the surrounding area consist of (1) high -intensity commercial and residential development that is primarily concentrated in the western portion of the project area, and (2) relatively undeveloped urban open space in the eastern half of the project area (Figure 3). Conditions in the general vicinity of the project are typical for highly developed areas with large amounts of paved surfaces, high levels of traffic, fragmented natural resource systems, and extensive stormwater management. The discussion that follows focuses on the area that extends 200 feet from the edges of the existing pavement of the affected corridors. Project staff chose this distance to determine the extent of the project area. Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 I-5 — SR 161/SR 18 Triangle Improvements Project February 2009 Washington State Department of Transportation EXHIBIT Page 5 PAGES GF �_ Figure 2 Le -end Project Limits Overview of In -Water Work Draft Stream Mitigation Plan C� Daylight Stream 1-5/SR 161/SR1 8Triangle Improvements --------- Channel Realignment 0 500 1,000 Feet � New Culvert/Culvert Extension I 1 I I I LEGEND: East Branch Hylebos Creek Subbasin Figure 3 West Branch Hylebos Creek Subbasin Project Area Drainage Subbasins C Corringtion Mitigation Site Draft Stream Mitigation Plan ;r . Project Area 1-5/SR 161/SR18Triangle Improvements Streams 0 0.25 0.5 Miles City Limits l r t .����-•-.-- PAGE 1b OF q(a 3.2 Streams 3.2.1 Hylebos Crook Basin The Triangle project area is situated in the upper reaches of the Hylebos Creek basin, which is part of the Puyallup/White Water Resources Inventory Area (WRIA)10. The 18 square miles of the basin are drained by more than 25 miles of streams in three major subbasins: West Branch (Tributary 0015), East Branch (Tributary 0016), and Lower Hylebos Creek (King County 1991; BERGER/ABAM 2006). Most of the Triangle project lies within the East Branch Hylebos Creek subbasin (Figure 2). Some project improvements west of I-5 lie within the West Branch Hylebos Creek subbasin. The Lower Hylebos Creek subbasin, which contains no project improvements, is south of the project area and includes the confluence of the Tributary 0016 and Tributary 0015 and other minor tributaries that eventually discharge to Commencement Bay through the Hylebos Waterway. Hylebos Creek was once a productive lowland stream that supported large runs of coho, chum, and Chinook salmon as well as steelhead and cutthroat trout (King County 1991). Significant land use changes have caused severe degradation to the surface waters of the basin. King County's 1991 basin plan identified threatened aquatic systems in the basin, including the Tributary 0016 ravine reach, which is the best area of existing fish habitat in the East Branch subbasin. The ravine reach of Tributary 0016 is located between the King/Pierce county line and Tributary 0015, which merges with Tributary 0016 about 0.7 mile south of SR 161 and the project area. This reach is located in a less developed, forested area in and just north of the City of Milton. A well -developed tree canopy shades the stream and serves as a source of recruitment for in -channel large woody debris. Gradients in the ravine reach of Tributary 0016 are steeper than the low gradients associated with tributaries 0016 and 0016A north of SR 161 and the stream is subject to erosion due to the presence of easily eroded sand and gravel of the Vashon advance outwash soils (King County 1991). In the early 1990s, observers recognized that the increased flows, sediment loads, and water quality degradation resulting from development were increasing erosion and sedimentation and degrading water quality that reduced the quality of fish habitat (King County 1991). Because of numerous fish passage barriers and the poor habitat that has resulted from intermittent flows, salmonid use of tributaries 0016 and 0016A in the project area is limited to resident cutthroat trout in Tributary 0016 (BERGER/ABAM 2007). Barriers at SR 161 and at culverts just north of the road crossing prevent salmonid species from using tributaries 0016 and 0016A within the project area. Tributary 0015 supports Chinook coho, and chum salmon, as well as steelhead and cutthroat trout. Surface water from a small portion of the project area west of I-5 (proposed South 356th Street offramp) will drain into the West Branch subbasin (Figure Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 I-5 —SR 161/SR 18 Triangle Improvements Project EXHIBIT February 2009 Washington State Department of Transportation + •. Page 8 PAGE _1_L_ . -OF tic, 3). Mitigation for project activities would take place at the Corrington mitigation site, also located in the West Branch subbasin. 3.2.2 East Branch Hylebos Creek Subbasnn Tributaries 0016 and 0016A, both tributaries of the East Branch Hylebos Creek, are located within the area of effect of the Triangle project (Figure 3). Both tributaries are located within the East Branch Hylebos Creek subbasin. Several area and project documents address the characteristics of these streams. ■ Executive Proposed Hylebos Creek and Lower Puget Sound Basin Plan (King County 1991) ■ SR 161 Hylebos Creek Stream Survey, OL 2713 (WSDOT 1997) ■ I-5 - SR 161/SR 18 Triangle Improvements Water Resources Discipline Report (BERGER/ABAM 2006) ■ I-5 - SR 161/SR 18 Triangle Improvements Fish, Vegetation, Wildlife, and Habitat Discipline Report (BERGER/ABAM 2007) ■ I-5 - SR 161/SR 18 Interchange Improvements Phase 1 Hydraulics Report (BERGER/ABAM 2008a) ■ I-5 - SR 161/SR 18 Interchange Improvements Fish Evaluation Passage Report (BERGER/ABAM 2008b) Table 1 below presents information about the streams and notes the regulated stream setback width in the project area. The stream setback is set by the City to protect the stream and its functions from adjacent development (City of Federal Way Zoning Code 22-1306). Tributaries 0016A and 0016 are considered by the City to be "major streams" under the zoning code with a 100-foot setback from the ordinary high water mark (OHWM) on each side of the stream. The regulated stream setback is sometimes referred to as a stream buffer or riparian area or zone. For convenience, this document refers to the 100-foot area on each side of the stream as the riparian area and riparian habitat. 3.2.3 Tributary 0016A The following stream description of Tributary 0016A comes principally from the I-5 - SR 161/SR 18 Triangle Improvements Fish, Vegetation, Wildlife, and Habitat Discipline Report (discipline report) (BERGER/ABAM 2007). Tributary 0016A originates in the vicinity of The Commons at Federal Way and flows directly south, roughly paralleling I-5 (Figure 3). South of South 336th Street, the channel runs parallel and adjacent to I-5, sometimes within 10 feet of the toe of the road embankment. Although most of this reach is confined to a narrow riparian corridor, shading is fairly good because of the dense tree growth. However, between South 341st and South 336th streets, there is a wide riparian zone. Nearly all of this reach was channelized during the construction of I-5. Draft Stream Mitigation Plan BERGER/ABAM, FAPWT4)4-064 I-5 — SR 161/SR 18 Triangle Improvements Project February �' y 2009 Washington State Department of Transportation EXHIBIT� — Page 9 PAGE-D---O_ Table L Streams In the Project Area Stream Stream type Salmonid- Bearing In Project Area Intermittent, Perennial, Seasonal Fish Passage Barriers Section 303(d) list Riparian Area/ Regulated Width of Stream Setbackal Tributary King County Yes. Perennial Several Downstream 100-foot setback 0016 Class 2 with Resident barriers Hylebos salmonids Cutthroat downstream Creek listed trout present and in for fecal No project area coliform anadromous salmonids due to barriers Tributary King County No a) Intermittent, Several Downstream 100-foot setback 0016A Class 2 with seasonal barriers Hylebos salmonids(l) downstream Creek listed and in for fecal project area colifonn (1) King County designates Tributary 0016A as a Class 2 stream with salmonids; however, salmonid presence is highly unlikely due to flashy hydrology and stream surveys have not documented their presence (WSDOT 1997). (2) City of Federal Way Zoning Code 22-1306 The riparian trees are now over 40 years old and encroach into the channel, creating pools during high flows where roots catch debris and form scour pools. The underlying layer (substrate) of the stream is composed primarily of fairly clean, small- to medium - size gravel. The reach has few food sources for resident fish, as the discipline team conducting the field investigation found no aquatic insects. Just north of the SR 18 interchange, the stream runs through a long culvert and around the edge of a new stormwater detention/treatment facility. During a site visit in June 2005, the discipline team observed that the culvert entrance was partially plugged with branches and leaves, which may be evidence that plugging often happens at this location. Upstream of this point, there is a reach, perhaps 50 yards long, where the stream bottom and banks are inundated with thick deposits of mud, with ponded areas at least 3 to 4 feet deep. Shading in this reach is good despite the narrowness of the riparian zone. Habitat in this reach is poor because of the heavy sediment deposition. The culvert on the downstream side of the southwest SR 18 interchange is perched (elevated), and is thus impassable by fish. The channel in the stream reach behind Costco and Home Depot, south of the SR 18 interchange, is elevated about 8 to 10 feet above the parking lots and buildings. The channel is confined between the buildings and I-5 in a narrow channelized corridor. Shading in this reach is good despite the narrowness of the riparian zone. The stream substrate is predominantly clean gravel with low amounts of siltation. There are a few quality pools formed by the root masses of trees on the streambank. Photos 1 through 3 show the typical condition of the stream in this area. Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 I-5 — SR 161/SR 18 Triangle Improvements Project EXHIBIT February 2009 Washington State Department of Transportation jj Page 10 PAGE 9a Photo 1- Tributary 0016A In back of Costco. Culvert outlet from the southwest cloverleaf ramp of SR 18. The wading staff to the left of the culvert Is 6 feet tall. Photo 3 - Tributary 0016A Just downstream of the 1-5 culvert. Water flows slowly through the reed canarygrass. Photo 2 - Typical riffle In Tributary 0016A. - i• "�,i� iV�ip ::Y7 - i�j _ r I' - Photo 4 - Inlet of Tributary 0016A culvert under 1-5. Near South 356th Street, the stream channel becomes exposed and is choked with reed canarygrass (Phalaris arundinacea), the dominant riparian plant in this area. At this point, Tributary 0016A crosses under I-5 (see Photo 4). On the east side of 1-5, the channel widens and is lined and choked with thick reed canarygrass here as well. The center of the channel is about 4.5 feet wide and contains pea gravel and small gravel that is fairly clean, at least on the surface. The discipline team could not observe the substrate condition, but it is undoubtedly silty; this condition exists from the I-5 crossing down to the stormwater pond access road off South 360th Street. The access road culvert and the South 360th Street culverts are impassable because of slope and water velocity characteristics. Both culverts were dry when visited. Because of the number and the condition of the culverts, as well as the poor habitat conditions, it is doubtful that fish could use this section of the tributary for spawning and rearing. Fish that are stranded here would not survive the seasonally dry Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 I-5 - SR 161/SR 16 Triangle Improvements Project February 2009 Washington State Department of Transportation . IT Page e 11 PMAG 1 Lf OFF conditions within the reach, except perhaps in deep pools (two pools were observed in March 2006).. Tributary 0016A drains a major portion of the runoff from the project area. A series of ditches and culverts collects runoff from both the east and west sides of I-5 and conveys it to Tributary 0016A. The lack of a perennial headwater source (such as a wetland or a lake) combined with the high proportion of impervious surface in the immediate subbasin result in rapid, high peak stream flows occurring with precipitation events. This situation results in highly flashy flow conditions in response to rain events (WSDOT 1997; BERGER/ABAM 2006, 2008a, 2008b). Stream gage data (Figure 4) show periods of zero flow from May to September and little to no base flow during the winter months (BERGER/ABAM 2008b). Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 1-5 — SR 161/SR 18 Triangle Improvements Project February 2009 Washington State Department of Transportation EX" 1 r T Page 12 i 3.00 g a 2.50 c = 200 ~ 1.50 IL z v Z 1.00 l m - 05 ! - 6, I d 0.00 M A N F M A N F M A N F M A N F M 1995 1995 1995 1996 1996 1996 1996 1997 1997 1997 1997 1998 1998 1998 1998 1999 1999 OBSERVED DAILY PRECIPITATION: LAKE DOLLOFF PRECIPITATION GAGE 40.0 OBSERVED 35.0 11 0 30.0 i m c � c�i c 25.0 Z W l _ W GG 20.0 1 = fu 15.0 N LL t r 10.0 s 1�; y. � •� 4f � t.} S4 �� SIf 5.0 �y • ' . .� S� les i 5. 0.0 M A N F M A N F M A N F M A N F M 1995 1995 1995 1996 1996 1996 1996 1997 1997 1997 1997 1998 1998 1998 1998 1999 1999 OBSERVED AVERAGE DAILY DISCHARGES: EAST FORK HYLEBOS TRIBUTARY 0016A KING COUNTY STREAM GAGE 24E SOURCE: King County Hydrologic Information Center (2007) Figure 4 Observed Flow Data for Tributary 0016A 1-5/SR 161/SR18Triangle Improvements Draft Stream Mitigation ft*a ra,h—y a��+ E ��9. Tributary 0016A has limited capability to support fish and other aquatic life because of the stream's intermittent and flashy flow (WSDOT 1997). These characteristics could result in fish stranding and high stream temperatures during low or zero flows and in channel scouring, increased turbidity, and lack of spawning substrate during high flows. Several culverts in the project area prevent the upstream passage of salmonids into the project area. These fish passage barriers include several additional culverts just north of SR 161(south of the previously referenced South 360th Street culverts), the I-5 cross - culvert, and culverts associated with the I-5/SR 18 interchange. Analysis of velocity and depth guidelines for fish passage indicates that the I-5 culvert is a velocity barrier for adult salmon migration and a depth barrier for downstream salmon migration (BERGER/ABAM 2008b). Stream survey results reported in the I-5 — SR 161/SR 18 Triangle Improvements Project Fish, Vegetation, Wildlife, and Habitat Discipline Report (BERGER/ABAM 2007) indicate that the average width of the channel of Tributary 0016A ranges from 5 to 15 feet and its depth averages 0.5 to 1.25 feet (see Photo 5). An electrofishing study by King County staff in 1996 and 1997 identified no salmonids in Tributary 0016A. The study report noted that even insect life was 'limited" (WSDOT 1997). Project -related stream surveys also noted the absence of aquatic insects (BERGER/ABAM 2007). Photo S. Tributary 0016A north of the SR 18/1-5 Interchange. Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 I-5 — SR 161/SR 18 Triangle Improvements Project February 2009 Washington State Department of Transportation EX PM M A Page 14 PACE _1.�,. ►...:f 3.2.4 Tributary 0016 The following stream description comes principally from the I-5 — SR 161/SR 18 Triangle Improvements Project Fish, Vegetation, Wildlife, and Habitat Discipline Report (BERGER/ABAM 2007). Tributary 0016 starts at North Lake and flows into Weyerhaeuser Pond. From there, the stream passes under the Weyerhaeuser Corporate Headquarters building and a grass field in a culvert about 0.5 miles long (see Photo 6). Downstream of the culvert outlet is a short reach of channel that flows through a thick riparian corridor down to the culvert under SR 18. The SR 18 crossing consists of two culverts (see Photo 7). Analysis of velocity and depth guidelines for fish passage indicates that the SR 18 culverts are velocity barriers for adult migration and depth barriers for downstream migration (BERGER/ABAM 2008b). These culverts will not be modified or extended by the project. Below SR 18, the channel is fairly low gradient and dominated by silt. The stream condition within this reach is dominated by shallow pools or slow water conditions (see Photo 8). The riparian area is generally wide, except where houses have encroached down to the stream channel and shading is generally good. A local resident reported seeing a dead 5-inch trout within this reach (BERGER/ABAM 2007). Farther downstream at the South 354th Street crossing, the stream channel is covered by a narrow strip of dense riparian growth This stream reach resembles the riparian corridor in the previous reach. The culvert under SR 161, which is outside the project area, is perched and impassable. Tributary 0016 has a history of coho salmon use and current use by cutthroat trout (WSDOT 1997; WSDOT 2007). An electrofishing study by King County staff in 1996 and 1997 identified no salmon in Tributary 0016 (WSDOT 1997). 3.3 Riparian Vegetation While the surrounding area has been subject to extensive high -intensity commercial and residential development, the uplands immediately adjacent to most of the project alignments exist as maintained highway right-of-way (ROW), urban forestland, and open space. These uplands have been subject to varying amounts of manipulation in the form of historic logging and agricultural practices, disturbance from past road construction activities, and ongoing road ROW maintenance. Except in a few locations, the first 50 feet of area adjacent to the existing roadway and gravel shoulders generally exists as a regularly mowed and maintained lawn area. Outside the immediate ROW, vegetation within the project area varies greatly and ranges from heavily impacted areas dominated by monotypic stands of Himalayan blackberry (Rubus armeniacus) or reed canarygrass to relatively undisturbed upland forestland with an overstory of Douglas fir (Pseudotsuga menziesii), big -leaf maple (Acer macrophyllum), and red alder (Alnus rubra). Draft Stream Mitigation Plan I-5 - SR 161/SR 18 Triangle Improvements Project Washington State Department of Transportation BERGEWABAM, FAPWT-O"" February 2009 E•XHI kTPage15 PAGE OF 4( Photo S. Looking at the Weyerhaeuser Corporate Photo 7. Mud -filled pool at outlet of Tributary 0016 Headquarters building from the culvert outlet of Tributary culvert under SR 18. The pod is backwatered by an 11- 0016. This advert extends all the way across this field inch -high rock weir about SO feet downstream. The rock and under the building to Weyerhaeuser Pond. dam Is outside of the SR 18 right-of-way. 'P% I Photo S. Typical mud -bottom glide habitat on Tributary 0016 downstream of SR 18. Note house on right. I-5 — SR 161/SR 18 Triangle Improvements Project Fish, Vegetation, Wildlife, and Habitat Discipline Report (BERGER/ABAM 2007) characterizes the plant communities in the project area and ROW. Six communities were identified and mapped in the study area. ■ Wetland s Riparian ■ Meadows/grassland ■ Developed/cleared land ■ Mixed deciduous/conifer ■ Maintained ROW Vegetation communities along tributaries 0016A and 0016 are a patchwork of mixed deciduous/conifer, developed/cleared land, riparian, wetland, and maintained ROW. The descriptions of the tributaries in the previous section provide relevant observations Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 I-5 — SR 161/SR 18 Triangle Improvements Project February 2009 Washington State Department of Transportation E 1 P 1TPage 16 PAGE t -1-OF � about the riparian areas. Some stream reaches include a well -developed riparian area that shades the stream and supports wildlife. Although the stream was channelized about 40 years ago with the construction of I-5, the riparian trees have encroached into the channel and created scour pools at some locations. Photo 9 shows a section of Tributary 0016A through the channelized section south of the SR 18/1-5 interchange. Other areas have been cleared and are dominated by reed canarygrass with limited habitat value. Photo 9. Tributary 0016A south of the SR 18/1-5 interchange. Note log weir and streambank stabilization with rock. Riparian areas are interrupted, particularly through the cloverleaf SR 18 interchange, at crossings of SR 18 and I-5, and where the stream is located in culverts. Figure 5 shows these breaks in the riparian areas along the tributaries. Before Tributary 0016A enters the culvert that passes under I-5, there are fewer trees and reed canarygrass dominates the riparian area and stream channel. On the east side of I- 5, downstream of the I-5 culvert, maintained ROW and mixed deciduous/conifer communities dominate the riparian vegetation south to SR 161. Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 I-5 - SR 161/SR 18 Triangle Improvements Project February 2009 Washington State Department of Transportation EXHIVIT Page 17 RAGE SOURCE Figure 5 LEGEND: RiparlanArea(10o-footsetback) Existing Riparian Habitat Areas >A—i RiparianExisting Are (1 1-5/SR 161 /SR1 8 Triangle Improvements Draft Stream Mitigation Project Area Streams Q 0 1,000 2,000 Feet =EE3r City Limlts Project Pathway ■ p` 'rrS R` f 99 C�'S PAGE Oil 011r" Cffe2 4.0 STREAM AND RIPARIAN AREA IMPACTS 4.1 Permanent Stream Impacts Extending culverts and placing fill within the stream channel as part of the project will result in permanent impacts to Tributary 0016A. Figure 6 shows the locations of these permanent stream impacts to Tributary 0016A and notes the project features associated with them. Table 2 presents estimates of permanent project construction impacts on Tributary 0016A by activity and construction phase. Table 2. Permanent Stream Channel Impacts Construction Activity Phase i Phase 2 Total Lineal Feet Lineal Feet Lineal Feet Culvert extensions 85 100 185 Channel abandoned and filled 495 - 495 New culvert - 65 65 745 The project will have no permanent impacts on the stream channel of Tributary 0016. 4.1.1 Culverts Culvert extensions will occur in association with the following project features (Figure 2). ■ New southbound offramp from I-5 to South 348th Street. The culvert that carries Tributary 0016A under South 348th Street will be extended to the north by 50 feet ■ New southbound onramp to I-5 from South 348th Street. The culvert that carries Tributary 0016A under the existing onramp will be extended to the south by 50 feet. a I-5 cross culvert. The culvert carrying Tributary 0016A from the west side of I-5 to the east side will be extended to the west by 85 feet. ■ A new culvert (65 If) carrying Tributary 0016A will be required at the location of the proposed South 356th Street offramp. The project does not propose to retrofit the culverts conveying Tributary 0016A because the upper reaches of Tributary 0016A lack sufficient water levels, are subject to flashy stream flows, and lack suitable fish habitat. Draft Stream Mitigation Plan I-5 - SR 161/SR 18 Triangle Improvements Project Washington State Department of Transportation EXHIBIT - PAGE 2: OF BERGER/ABAM, FAPWT-04-064 February 2009 Page 19 r< Federal Way g� rl J, JI � J� �T t I� . � r I II Culvert Extension r (50 feet) + _1 Culvert Extension I (50 feet) o � I Weyerhaeuser Pond 0 Fill existingchannel 1 King County (495 feet) 1-5 cross -culvert extension (35 feet) V NewCUkmft (65 feet) / I i ` North Lake Lake Killarney Figure 6 Stream Impacts Draft Stream Mitigation Plan Legend 1-5/SR 161/SR18 Triangle Improvements Project Limits New Culvert/Culvert Extension 0 500 1,000 Feet ( I I I I EXPIRMT n A c-, r_' '7 2 c-: �- Lit 4.L2 Tributary 0016A Channel FIII Widening for the CD road between southbound I-5/westbound SR 18 and SR 161 and new ramps to SR 161 at South 356th Street and South 359th Street will require extensive amounts of grading and roadbed preparation. The existing road alignments and the location of the Tributary 0016A channel mean that making the proposed transportation improvements will result in permanent impacts to Tributary 0016A. The necessary grading activities will result in the abandonment and filling of approximately 495 feet of Tributary 0016A. 4.L3 Stream Function Impacts Extending culverts that carry Tributary 0016A under existing roadways will eliminate 250 feet of open stream channel at the locations shown in Figure 6. The stream channel provides low habitat functions as result of extended periods of low or non-existent flows (see Photo 10). Other factors that contribute to its poor quality include precipitation - driven flashy peak flows and related channel scour, periods of high turbidity, sedimentation, and the lack of spawning substrate. Photo 10. Dry channel of Tributary 0016A In October 2005. Location of picture is west side of 1-5 south of the SR 18/1-5 Interchange near the location of the proposed southbound offramps to SR 161 at South 356th Street. Channel fill and abandonment will require a relocated/realigned channel to maintain the stream's hydraulic and habitat functions. The proposed new channel construction can Draft Stream Mitigation Plan 1-5 — SR 161/SR 18 Triangle Improvements Project Washington State Department of Transportation EXHIBIT � PAGE-zq BERGER/ABAM, FAPWT-04-064 Febivary 2009 Page 21 be done `off line" to avoid water quality impacts to downstream waters. The proposed new channel and associated riparian area alignment will be completed at the same time as the abandonment of the existing channel alignment. Temporary stream function impacts are anticipated because of the organic input will be reduced and macroinvertebrates will be lacking while vegetation becomes established along the new stream corridor. 4.2 Riparian Impacts The project activities will result in permanent and temporary impacts to the riparian vegetation associated with tributaries 0016A and 0016 (Figure 7). These impacts will result in a permanent loss of vegetation within riparian areas where new facilities are built. Temporary impacts will result from the need to clear vegetation to allow construction access. The construction of a stormwater pond will result in permanent riparian area impacts to Tributary 0016, on the south side of SR 18. Temporary impacts to the riparian area of Tributary 0016 may be required to construct a retaining wall on the north side of the SR 18 stream crossing. This riparian area is also regulated as buffer for Wetland M. Mitigation for these temporary impacts is addressed in the wetland mitigation plan (BERGER/ABAM 2008c). Table 3 presents estimates of permanent and temporary impacts to riparian areas resulting from the permanent placement of project facilities and temporary construction activities. The estimate for temporary riparian area impacts includes expected staging areas and a 15-foot offset from the base of permanent improvements. Following construction, these temporary impact areas will be replanted and restored. Permanent riparian area impacts from project facilities, such as walls, foundations, and road embankments, are also included in the table. The impact acreages include buffer areas that are also regulatory wetland buffers due to the presence of wetlands within the riparian areas. T..hls A Rare nnnf snA Tarnnnrrary Rinarlan Ruffar Aran lmnar-4q (aorta] Impacts to -- - - Phase 1 Phase 11 Total Amount of Riparian Buffer Areas Riparian Buffer Areas Riparian Buffer Areas Impact Permanent Tributary 0016A 1.62 2.82 4.44, Impacts Temporary Tributary 0016A 0.422 0.86 1.283 Impacts Permanent Tributary 0016 0.20 0.20 Impacts I Includes 0.43 acre of impact to shared wetland buffers 2 An additional .21 acres of temporary impacts will occur in phase I but will become permanent in Phase Il. They are only accounted for as permanent impacts. 3 Includes 0.26 acre of impact to shared wetland buffers Draft Stream Mitigation Plan BERGER/ABAM, FAPWT4)4-064 I-5 — SR 161/SR 18 Triangle Improvements Project February 2009 Washington State Department of Transportation EX H I IT = Page 22 5 PAGE 2 OF a:6 1 i i Federal Way Weyerhaeuser i Pond 0016A Riparian Area 1 p Encroachment (0.37 acre) - i I 18 !t 0016A Riparian Area Encroachment (0.9 acre) i J 0016 Riparian Area Encroachment 0016A Riparian Area (0.20 acre) i t I Encroachment (2A7 acre) tf ] V. ] 1 i =r' King County Lake f 0016A Riparian Area Killarney / F Encroachment / (0.20 acre) ` E i' P ? 00.16A Riparian Area Encroachment _ 1 (0,50 acre)! j I j 6 Legend Figure 7 Project Limits Riparian Area Impacts © 100 fl Riparian Area Draft Stream Mitigation Plan --- —- —• Stream 1-5/SR 161/SR18Triangle Improvements Riparian Encroachment Areas . ❑ SOQ 1,000 Feet I t i i I EA IT Temporary impacts will involve vegetation clearing to allow access by construction equipment and will introduce noise and other disturbances to these stream riparian areas. These impacts will disrupt small mammal and bird usage temporarily until vegetation becomes re-established along the edge of the remnant community. Because all construction activities can be accomplished when stream flow is very low or can be bypassed easily from active work areas, they likely will have little impact on water quality in Tributary 0016A or downstream branches of Hylebos Creek Construction activities within riparian areas would increase the potential for the spread of nonnative invasive and noxious plant species (BERGER/ABAM 2007). However, WSDOT will plan and implement appropriate revegetation measures to minimize this potential. 4.3 Stream Impact Summary The Triangle project will not affect the stream channel of Tributary 0016 directly but will permanently encroach on its stream setback area. The construction of the retaining wall at the stream crossing of SR 18 may alter the vegetation in the setback area of Tributary 0016 temporarily, but this alteration will be minor in extent. Construction of the Triangle project will have the following impacts on the stream channel of Tributary 0016A and its associated riparian area within the regulated 100-foot setback area. ■ The project will enclose 250 feet of Tributary 0016A in new culverts (65 feet) and culvert extensions (185 feet) (Figure 6). ■ 495 feet of Tributary 0016A will be filled and the stream relocated (Figure 6). a Encroach into an estimated 4.44 acres of riparian habitat, principally mixed deciduous/conifer forest, Himalayan blackberry thickets, and roadside grass fields (Figure 7). ■ The project will temporarily impact an estimated 1.28 acres of riparian area along Tributary 0016A. Retention of existing fish passage barriers at project area culverts on Tributary 0016A. 5.0 STREAM MITIGATION ACTIVITIES 5.1 Overview The development of the Triangle project has involved a multidisciplinary approach that included engineering and environmental disciplines. As the project developed, the project team identified a range of alternatives to reduce congestion and improve safety. They were screened in a two-phase process with 28 criteria, including environmental criteria. The proposed build alternative received the top score in the environmental effects category by keeping most of the improvements within the existing ROW and causing the fewest impacts to the natural environment. Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 I-5 — SR 161/SR 18 Triangle Improvements Project EXHIBIT February 2009 Washington State Department of Transportation Page 24 PAGED `_ Even so, some unavoidable impacts to stream resources will occur as a result of project construction. The following discussion proposes several mitigation activities aimed at offsetting project impacts to project area streams and associated riparian habitat. The intent of this list is to provide conceptual descriptions of the offsetting mitigation activities to further discussion among members of the project team and reviewing agency staff. 5.2 Mitigation Approach The Triangle project took a watershed/landscape approach to mitigate impacts caused by construction. This approach does not necessarily result in a 1:1 ratio of impacts to mitigation; however, it does address existing habitat limiting factors, such as the flashiness of the stream and the water quality of the runoff. Mitigation activities include stormwater quality and quantity retrofits, removal of existing culverts, and creation of new stream and riparian habitat within the project limits. The project will also provide mitigation for existing fish passage barriers through the creation of fish habitat at the Corrington mitigation site. Table 4 summarizes project impacts and corresponding mitigation. 5.3 Table 4. lM act and Mitigation Summary Activity Impact Mitigatlon Stream Channel + 185 ft culvert extension • Stormwater control and and Buffer + 495 ft channel fill treatment retrofit for 34.10 • 65 ft new culvert acres of impervious surfaces. + 4.44 acre riparian buffer loss • 2.45 acres buffer enhancementand creation • 51.5 ft of new channel • 250 ft of culvert removal and channel restoration Fish Passage + Retain existing fish passage 0 1.08 acre riparian buffer barriers enhancement a 412 If/0.19 acre off -channel stream habitat Stormwater Quality and Quantity Retrofit In addition to building facilities to detain and treat the project's proposed 14.7 acres of new impervious surfaces, the Triangle project will provide water quality and stormwater control for 34.10 acres of existing impervious surfaces of 1-5 and SR 18. Much of the runoff from SR 18 and 1-5 is currently collected by catch basins and roadside ditches and is conveyed, untreated, directly to tributaries 0016 and 0016A. The recently completed SR 5 Pierce County Line to Tukwila I/C — HOV Stage 4 project included collection, treatment, and detention of runoff from the new pavement, as well as a portion of the existing 1-5 pavement, that drains to the median. This project will incorporate similar improvements for SR 18 and I-5. The proposed stormwater facilities include a combination of treatment, detention, and conveyance improvements, including: Draft Stream Mitigation Plan I-5 — SR 161/SR 18 Triangle Improvements Project Washington State Department of Transportation EXHIBIT � PAGE 2 8 n; 1h. BERGER/ABAM, FAPWT-04-064 February 2009 Page 25 ■ Media filter drains for treatment of highway runoff ■ Constructed wetland/ponds (one new and two reconstructed) for detention and treatment ■ Vault for detention and treatment • Enclosed drainage systems for conveyance ■ Channel realignment for conveyance of Tributary 0016A (Section 5.4) These proposed facilities address both the water quality and water quantity limiting factors listed for East Branch Hylebos Creek in the WRIA 10 Salmon Habitat Report (Kerwin 1999). The type of treatment varies between the drainage basins within the project area (Figure 8). Enhanced treatment is required for highways that discharge to streams by the WSDOT Highway Runoff Manual (HRM)(June 2008) and involves methods that remove dissolved metals as compared to basic treatment which only removes total suspended solids. 5.3.1 Basin B The proposed stormwater facility for Basin B is a combined wet/detention pond in the southwest loop of the I-5/SR 18 interchange. Tributary 0016A and Wetland U are located in the center of the loop. Pond B would be located in the western portion of the loop to reduce stream effects to Tributary 0016A. Stormwater runoff from most of SR 18 and ramps to and from 1-5 currently sheet flows into ditches that parallel SR 18 and is discharged directly into Tributary 0016A. A proposed stormwater conveyance system, consisting of storm drainpipe and structures, will collect the runoff from SR 18 and all new impervious surfaces and convey it to Pond B for detention and treatment. 5.3.3 Basin C The proposed stormwater facility for Basin C is a combined stormwater treatment wetland/detention pond located south of SR 18 and west of Tributary 0016. Stormwater runoff from SR 18 and ramps to and from Weyerhaeuser Way currently sheet flows into ditches and storm drainpipes that parallel SR 18. A proposed stormwater conveyance system will collect the existing runoff from SR 18 and all new impervious surfaces and convey it to Pond C where it will be treated and detained prior to discharge into Tributary 0016 near the downstream side of the parallel SR 18 Culverts. In addition, 1,165 linear feet of media filter drain will be used to provide treatment in this basin. Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 1-5 - SR 161/SR 16 Triangle Improvements Project ` - February 2009 �XWashington State Department of Transportation lY■ M1O Page 26 �), 5 IMT11 51 NORTH f 4jl�YN/ LAKE FE RAL WAY q - BASIN R R ASIN C SR99 BASIN Bj1 �/ s BA IN I ` sits � - 1 i L411E BASIN D BASIN S 1� D BASIN G - T J - J rl rl MLAIfE Figure 8 Stormwater Drainage Basin Map Draft Stream Mitigation Plan Legend 1-5/SR 161/SR18 Triangle Improvements City Limits Streams 0 0 500 1,000 Feet I 1 1 1 I EXHI I T DA P- c /I_I 5.3.7 Basin D The proposed stormwater facility for Basin D is a vault in the northwest comer of the South 356th Street/SR 161 intersection. Stormwater runoff from SR 161 currently flows north through the South 356th Street/SR 161 intersection in a closed conveyance system without any treatment or detention. Runoff from improvements to this intersection and the South 356th Street offramp will be collected and treated in a vault in the northwest comer of the intersection. The addition of the vault will provide water quality and detention for the new impervious surface and compensatory area from Basin G. Due to ROW limitations and the urban development along SR 161, no property was available for an above -ground facility. The existing conveyance system will be retrofitted for the proposed improvements along SR 161 and the South 356th Street/SR 161 intersection. The stormwater from the vault will be discharged back into the enclosed system that conveys stormwater north along SR 161. 5.3.6 Basin G The stormwater for Basin G will sheet flow off the roadway into ditches. Compensatory treatment and detention will be provided in Basin D. A detention facility was not practical in Basin G because of limited ROW. The outfall from Basin G is approximately 2,500 feet south, making it not cost-efficient to convey the stormwater to the HOV pond located near the southbound weigh station. 5.3.5 Basin I The proposed stormwater facility for Basin I is a vault in the southwest corner of the South 348th Street/ SR 161 intersection. Stormwater currently sheet flows into roadside ditches that parallel SR 18 and flow towards South 348th Street entering an enclosed system. The stormwater runoff on the north side of SR 18 will tie into the existing system at South 348th Street. Runoff from the south side of SR 18 will be collected and treated using media filter drains, storm drainpipe, and structures. Due to ROW restrictions, a stormwater pond was not a viable option. 5.3.2 Basin R The stormwater retrofit for this basin will be accomplished by expanding the existing Pond R located on the west side of I-5 north of South 344th Street which was constructed for the SR 5 Pierce County Line to Tukwila I/C - HOV Stage 4 project. Stormwater runoff from the crown of the northbound lanes currently sheets flows into ditches and is discharged directly to Tributary 0016A. A new stormwater conveyance system will be constructed to collect and convey this stormwater to the expanded Pond R for treatment and detention prior to discharge to Tributary 0016A. 5.3.4 Basin S The proposed stormwater facility for Basin S is the expansion of Pond S, which was constructed for the SR 5 Pierce County Line to Tukwila I/C HOV - Stage 4 project. Pond S is located east of I-5 and north of SR 161. Pond S is a combined stormwater treatment wetiand/detention pond. Stormwater runoff from the crown of the southbound lanes to the outside edge of pavement currently sheet flows into ditches that parallel 1-5 and Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 1-5- SR 161/SR 18 Triangle Improvements Pro*d� � �� February 2009 Wad iVon State Department of Transportation Page 28 PAGE 3 L_ 0F 41,3 discharge the untreated runoff directly into Tributary 0016A. A proposed stormwater conveyance system will collect the runoff from the existing two lanes and all new impervious surfaces in Basin S and convey it to Pond S for detention and treatment prior to discharge to Tributary 0016A. Table 5 summarizes the new impervious surface areas by basin and the total area proposed for basic and enhanced treatment. Table S. Stormwater Treatment Summary Drainage Basin New Impervious (acres) Basic Treatment Provided (acres) Enhanced Treatment Provided (acres) B -1.2 8.6 8.6 C 5.1 6.3 6.3 D 1.3 2.6 0 G 0.9 0 0 1 0.3 1.7 0 R 3.0 10.4 10.4 S 5.9 8.8 8.8 Totals 12.8 38.4 34.1 These proposed features will provide significant improvements to projected annual pollutant loads delivered to Hylebos Creek. Table 6 compares annual pollutant loads of the build alternative versus the no -build alternative. The proposed project would reduce annual total suspended solids (TSS) pollutant loading by approximately 30 percent, phosphorous loading by 71/o, zinc loading by 24%, and copper loading by 28% when compared to the no -build alternative. Table 6. Comnarlsorr of Annual Pollutant Loads (Pounds per Year) Watershed Basin No -Build Alternative TSS Total Ph Total Zn CU West Branch of Hylebos Creek 16,529 34 10 2 Tributary 0016A 32,089 67 20 4 Tributary 0016 1 4,520 9 3 1 Totals 1 53,138 110 33 7 Watershed Basin Build Alternative TSS I Total Ph Total Zn I CU West Branch of Hylebos Creek 10,653 29 7 2 Tributary 0016A 22,275 62 15 3 Tributary 0016 3,990 11 3 1 Totals 36,919 102 25 5 Draft Stream Mitigation Plan I-5 - SR 161/SR 18 Triangle Improvements Project Washington State Department of Transportation BERGER/ABAM, FAPWT-04-064 February 2009 Page 29 PAGE 77-�OF 41(a The added detention will help address the highly flashy flows characteristic of Tributary 0016A and provide a more regulated downstream discharge during and after precipitation events, which are the principal driver of the tributary's flows. Figure 9 presents the effect of proposed Pond S (located east of I-5 north of SR 161 within Basin S). The figure shows a series of small precipitation events in April 1997 and the effect of the detention pond. The analysis for Pond S shows a reduction of the hourly peaks by approximately 20%. Treatment facilities planned in other basins are expected to see similar results. The runoff peaks will be detained and spread out, which will provide a steadier discharge rate into the stream. The moderated flows discharged from the project detention facilities and the water quality improvements provided by the project's drainage facilities will potentially reduce erosion and improve water quality in downstream reaches of Hylebos Creek where higher quality fish and aquatic habitat exists. The "ravine reach" of Tributary 0016, in particular, has been identified as an area of good fish and aquatic habitat. The reach, however, has been affected by increased peak flows and pollution generated by rapid land use development in upstream areas, including the project area. The project proposes drainage facilities that will reduce channel erosion and sedimentation and increase water quality in Hylebos Creek downstream from the project area to the benefit of fish and other aquatic life. SA Stream Relocation and Restoration The Triangle project will create and/or restore approximately 765 feet of seasonal stream habitat in phases 1 and 2 of construction. Approximately 250 feet of stream restoration will come from culvert removal and 515 feet from channel relocation. In Phase 1, the project will fill and abandon about 495 feet of the existing channel of Tributary 0016A and realign the channel as shown in Figure 10. A new approximately 580-foot channel will meander to the west to allow for the new offramp from I-5 to SR 161 at South 356th Street. The new channel will meander back south and east through the new offramp embankment to the existing 1-5 culvert, which will be extended. Phase II will install a new 65-foot-long culvert for the construction of the South 356th Street ramp, reducing the total length of the channel to 515 feet. This culvert will be designed and sized to satisfy fish passage design criteria consistent with the WSDOT Hydraulic Manual and the WDFW Design of Road Culverts for Fish Passage. Draft Stream Mitigation Plan I-5 — SR 161/SR 18 Triangle Improvements Project Warhingt on State Department of Transportation EXHIRI ' PAGE_,_ 33 OF.�f1� BERGER/ABAM, FAPWT-04-064 February 2009 Page 30 0.35 p z ------- PREDEVELOPED w 0.30 POSTDEVELOPED a 0.25 � 1 + S !1y LN LLI 0.20 ° 11 ii V p 0.15 ;;I ' �; �W 0.10 i 0.05 r 1 "� ILA �yil 1 MI 1 ; p 0.00 1997 Apr 13 1997 Apr 20 1997 Apr 27 1997 May 04 1997 May 11 POND S AVERAGE HOURLY DISCHARGE: EAST FORK HYLEBOS TRIBUTARY 0016A Figure 9 Detention Pond Effect on Peak Flows 1-5/SR 161/SR1 8 Triangle Improvements Draft Stream Mitigation EXHI u fi In Phase 2, the project will remove the loop ramp and two existing culverts in the northwest loop of the SR 18/I-5 interchange. This will allow approximately 250 feet of Tributary 0016A channel to be daylighted and restored. As required by the City's zoning code (Article XIV, Division 5), the stream design will reflect the following as appropriate. ■ A natural meander pattern ■ Gentle side slopes, at least 2:1 ■ Erosion control features for stream side slopes ■ Creation of a narrow subchannel, where feasible, against the south or west bank ■ Use of natural materials wherever possible ■ Native riparian vegetation The City's code also requires, where appropriate or feasible, that the design create spawning and nesting areas, re-establish the fish population, and restore flow characteristics compatible with fish habitat areas. In terms of the creation or restoration of a channel for Tributary 0016A, these latter requirements are not feasible or appropriate. The intermittent and seasonal flows of the tributary do not support populations of fish and other aquatic organisms adequately. Similarly, the high peak flows in Tributary 0016A followed by low or zero flows make for poor potential for establishing conditions suitable for spawning and rearing. The restored stream channel will be constructed by clearing the existing vegetation along the proposed alignment and excavating the proposed channel. Because of the relatively intact nature of this forested area, efforts will be undertaken to preserve existing vegetation close to the proposed stream alignment. Because of the existing grade, it will be necessary to clear areas on both sides of the stream to accommodate the stream channel and meet the maximum 2:1 slopes. The stream channel will consist of imported stream substrate with deflector logs and log boles installed at appropriate intervals and locations to increase habitat diversity. The banks will typically be constructed at a 3:1 slope and consist of amended soil and coir matting to reduce the potential for erosion. Construction will occur in isolation from stream flows to avoid in - water work and the potential for erosion. Before water is diverted to the new channel, all stabilization will be in place. 5.5 Riparian Habitat Creation/Enhancement The project will create and enhance an estimated 2.45 acres of forested riparian habitat around the relocated and restored stream channels (Figure 10). The plantings will establish a native forested plant community that will shade the stream channel and support the wildlife that now uses the mixed deciduous/conifer habitats in the project area. Draft Stream Mitigation Plan I-5 — SR 161/SR 18 Triangle Improvements Project Washington State Department of Transportation EX 117-74T PAGE BERGER/ABAM, FAPWT-04-064 February 2009 Page 33 Following the construction of the relocated and restored stream channel and grading of the site as described in Section 5.4, the site will be planted with four distinct plant communities. Table 7 lists the proposed plant species for each of the four communities. The Emergent Bottom zone will occur along low-lying fringes, below the OHWM of the new creek channel, but not directly within the active channel. Plugs will be installed at a rate of 30,000 per acre and in clusters of 50 plants, with clusters spaced approximately 8 feet apart. Since plantings within this community will be sparse, planting locations will be established where appropriate conditions exist. The Riparian Emergent zone will occur adjacent to and above the OHWM of the creek in seasonally and occasionally inundated areas. It typically will occur on the 2:1 slopes from the OHWM to the top of bank. Plugs will be placed at a density of approximately 30,000/acre. Plugs should be installed in clusters of 50 plants, with clusters spaced approximately 8 feet apart. A Riparian Forest/Scrub-shrub zone will be planted in a band approximately 50 feet wide and extending outward from the top of bank of the new channel. Planting within this area will serve to provide shading of the channel, future large wood debris recruitment, wildlife habitat, and a source of nutrients for the stream. The remaining buffer will consist of an Upland Riparian Forest zone. This area would consist of interspersed plantings within the existing forest community from the edge of the riparian scrub -shrub community to the edge of the 100-foot riparian setback. The species composition would be selected to match the species within the existing forest community closely. Draft Stream Mitigation Plan I-5 — SR 161/SR 18 Triangle Improvements Project ! }� �� Washington State Department of Transportation �► fi X..f� RAG?. �%F� BERGER/ABAM, FAPWT-04-064 February 2009 Page 34 Table 7. Riparian Enhancement and Restoration Plant Ust Common Name Scientific Name Emergent Bottom Small Fruited Bulrush Scirpus microcarpus Bur -reed Sparganium emersum Bur -reed Sparganium eurycarpum Hardstem Bulrush Scirpus acutus Riparian Emergent Marsh Speedwell Veronica Sp. Slough Sedge Carex obupta Bur -reed Sparganium emersum Creeping Spike Rush Eleocharis palustris Dwarf spike rush Eleocharis parvula Riparian Forest/Scrub Shrub Red alder Alnus rubra Red twig dogwood Cornus stolonifera Oregon ash Fraxinus latifolia Pacific ninebark Physocarpus capitatus Black cottonwood Populus trichocarpa Willow Salix sp. Hardhack Spiraea douglasii Western red cedar Thuia plicata Red alder Alnus rubra Upland Riparian Forest Vine Maple Acer circunatum Big leaf maple Acer macrophyllum Beaked hazelnut Corylus cornuta Oceanspray Holodiscus discolor Indian plum Oemlaria cerasiformi Douglas fir Pseudotsuga menziesii Snowberry Symphoricarpos albus Red elderberry Sambucus racemosa Western hemlock Tsuga heterophylla To the extent possible, mature vegetation will be retained during construction by limiting equipment to one side of the channel. Invasive species will be removed from the riparian enhancement and creation area where not cleared during construction. In those areas, supplemental plantings will occur as necessary to insure appropriate plant density. Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 I-5 — SR 161/SR 18 Triangle Improvements Project EXHIBIT-!- �� �� February 2009 Washington State Department of Transportation Page 35 PAGE-3-8-OF In addition to the plantings, habitat improvement structures, including brush piles, snags, and bat boxes, will be installed within the areas. The project team will oversee the construction of six brush piles per acre within the relocated and enhanced riparian areas to provide cover from predators, assist thermal regulation, provide nesting areas, and increase insect populations for birds and other insectivores. Brush piles will be at least 10 feet in diameter and 5 feet high and constructed of native woody debris layered in a crisscross pattern with the largest debris on the bottom and smallest debris set on top. Typical Brush Pile Bottom Typical Brush Pile Top The illustrations above are a general guideline. To ensure proper construction and placement, brush pile construction in the field will be assisted by a qualified biologist. To provide habitat for cavity nesting birds and mammals, at least two snags per acre will be installed in the relocated and enhanced riparian areas. Snags will be at least 24 inches in diameter and at least 20 feet tall and if possible will contain two stems. The plan calls for placing snags upright in an excavated hole with a depth that is approximately equal to one -quarter of the total length of the snag, backfilling the hole with native material, and compacting the soil to ensure stability of the snag. To avoid property damage, the installer should exercise best professional judgment in the field during installation. Bat boxes will be installed to replace and augment roost sites. Two boxes will be installed per acre and will consist of either chamber boxes or rocket boxes. Chamber boxes will be installed directly to the top third of the proposed snags. Rocket boxes will be installed where suitable conditions exist. Suitable locations will be at least 15 feet off the ground, afford maximum sun exposure, and be relatively free of obstructions within a 15-foot diameter. Boxes will contain multiple chambers and be constructed consistent with WDFW recommendations. These enhancements will increase the functional value of the riparian habitat, which currently is highly degraded by the uniform reed canarygrass community that dominates the area around the stream in the channel fill impact area (see Photo 11). The enhancements will increase stream riparian and wildlife functions by increasing plant diversity, foraging and nesting habitat, overall habitat complexity, and plant structure Draft Stream Mitigation Plan f BERGER/ABAM, FAPWT-04-064 �� I-5 — SR 161/SR 18 Triangle Improvements Project @ I February 2009 Washington State Department of Transportation PAGE -M-O FPage 36 diversity. A diverse plant community along the stream channel will also contribute to the production and export of organic matter to the stream system. 5.6 Off -Channel Fish Habitat Creation Because of the low base flows and flashy nature of Tributary 0016A, and the lack of suitable fish habitat within the stream reaches above the existing fish barriers, removing the existing fish barriers will not improve habitat for fish species significantly. To restore fish habitat within tributaries 0016A and 0016 within the project area to a level where fish passage improvements would result in a benefit would require significant additional habitat improvements including additional fish barrier retrofits, riparian enhancements, and stormwater retrofits including: ■ Additional stormwater retrofits for urban development contributing to Tributary 0016A to address base flows and flashiness; ■ Retrofitting seven fish passage barriers downstream of the project area on Tributary 0016A and five fish passage barriers on Tributary 0016; ■ Removal of culverts from and restoration of Tributary 0016A north of SR 18; and ■ Channel rehabilitation on Tributary 0016A downstream of I-5 culvert. Completing these improvements would provide access to 8,250 linear feet of additional stream habitat on Tributary 0016A within the project area and additional stream area upstream of the project area. However, the above improvements are not likely to address the flow issues within Tributary 0016A sufficiently for the stream to become suitable for anadromous fish. To mitigate for the lack of fish passage improvements along Tributary 0016A, the project will construct off -channel fish habitat at WSDOT's Corrington mitigation site. Since the Corrington site adjoins the North Fork of West Branch of Hylebos Creek, which has better habitat than Tributary 0016A and documented anadromous fish use, the added channel will provide a greater benefit to fish species than removing the fish barriers. New off -channel habitat will increase the amount of available fish habitat in the reaches of North Fork of West Branch of Hylebos Creek used by anadromous and other resident fish species. The project will excavate a channel averaging 3 feet wide and 2 feet deep in the wetlands (refer to Sheets 2 and 3, Appendix D Draft Wetland Mitigation Plan I-5 — SR 161/SR 18 Triangle Improvements Project). Sheet 4 of Appendix D details the proposed cross- section of the stream. Water depths within the channel are expected to be relatively constant between 18 and 24 inches. This channel will start near the pond outfall channel in the central portion of the Corrington site, meander through the enhanced wetlands, and ultimately outfall to the North Fork of West Branch Hylebos Creek (Figure 10). The channel will receive flows that currently flow through the pond outfall channel and outfall to the North Fork of West Hylebos through a small corrugated culvert. The water source for the pond is perennial and is composed of cool and clean groundwater Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 I-5 — SR 161/SR 18 Triangle Improvements ProjectFebruary 2009 Washington State Department of TransportationEX11113-IT Page 37 PAGES OP1z discharges from the wetlands east and north of the project site. This water source flows year round and water levels were observed to remain constant throughout the year. The proposed channel and wetland creation areas adjacent to the pond are not anticipated to change the level of water in the pond. The soils within the wetland areas that the outflow channel will be created in are listed as Shalcar muck Shalcar muck soils are moderately permeable soils that are very poorly drained and are high in organic content. Soil samples taken during the wetland delineation of the Corrington site confirmed the presence of Shalcar soils within the channel creation areas. The upper 5 to 10 inches of the soil are very high in decomposed organic matter mixed with a matrix of silt loam material. Deeper in the soil profile (below 12 inches) the soil transitions to a sandy loam material with inclusions of clay. Below approximately 18 inches, the soil is a mixture of sandy silt loam and sandy clay loam more similar to Snohomish silt loam soils that are listed by the NRCS as a minor component to the Shalcar series. The proposed channel will result in excavation within the wetland areas to depths approaching 3 feet (Appendix D, sheet 3). It is anticipated that the dominant material within the created streambed will be the clay loam material encountered below 18 inches. Erosion is not expected within this soil due to the very low overall slope of the created channel (0.98%). The construction of the channel will be completed in stages in coordination with the grading and other enhancement activities within the project site. Following the mowing and spraying of the reed canarygrass stands, the grading of the stream channel will be completed in conjunction with the other required grading on the Corrington site. The beginning and end of the stream channel will be isolated from the surface waters of the pond and North Fork of West Branch of Hylebos Creek with temporary cofferdams constructed from plastic sheeting and sandbags. The channel will be covered with a tarp material designed to eliminate the reed canarygrass from the site. Following the removal of the tarp material and hydro -seeding of the site, the cofferdams will be removed and surface waters allowed to flow through the new channel. The last stage of the channel construction will be the removal of the existing culvert on the pond outflow channel. A small backhoe will remove the existing culvert and the area previously occupied by the culvert will be backfilled with compacted soil. Prior to removal, the area will be isolated with cofferdams similar to those used for the new stream channel. This plan will allow surface waters to continue to circulate through the pond while at the same time providing valuable off -channel habitat for resident and migratory fish. It is anticipated that, over time, the backwater area between the entrance to the created channel and the old location of the culvert will silt in as suspended sediment settles out. The open water channel will make it easier for fish to access the resting and feeding opportunities in the pond. To enhance the amount of available fish habitat within the pond, several large softwood logs will be placed within it. In addition to providing egg laying opportunities for amphibians and basking habitat for turtles, these logs will Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 1 5 — SR MISR 18 Triangle rmprn is Project February 2009 Washington State Department of Transportation EX H F S I ■ � Page 38 PAGE �-OF&- N. Fork West Branch Llylebos Wetland A acre) r .► S 336th St ♦ Wetland B (0.01 acre on -site) Wetland Creation (0.09 acre) r bOFo9 # •���A•♦••Yy +�+ �0drWW+A rAml r rEL# �w1i#wf r e A �fia%!/i. 4+ + `. 1 1 •//J//,��Jrr�irf�; +i ++r eservation ��►���*1 lei+ S 0.06 acre 4 ' Off -Channel Hab tat 430 Li 1 Wetland Creation = 0.32 acre Wetland Enhancement -1.37 acres Wetland Buffer Enhancement =1.05 acres Riparian Enhancement Area =1.08 acre Off -Channel Habitat = 0.19 acre Wetland Enhancement area within 75' Paper Buffer = 0.60 acre Wetland Creation area within 75' Paper Buffer = 0.04 acre Legend Figure 11 Project Area _ Delineated Wetland Brush Pile Conceptual Mitigation Plan Stream Off -Channel Habitat i * Large Woody Debris Draft Stream Mitigation Plan CulvertRemoval x® Wetland Buffer Enhancement _ 1-5/SR 161/SRI8 Triangle Improvements 75' Paper Buffer ® Wetland Creation - _ _ Upland Preservation -- Riparian Enhancement Area Wetland Enhancement e 0 40 80 Feet I 1 I I EXISIR 1T WI-1AE_43_0 Photo 11. Dry channel of Tributary 0016A in October 2005. Photo taken where the existing stream channel will be filled and relocated to the west (left). Channel overgrown with reed canarygrass 6.0 MITIGATION OBJECTIVES AND PERFORMANCE STANDARDS 6.1 Mitigation Goals The goals of the proposed mitigation are to replace lost habitat with improved habitat that addresses existing habitat limiting factors in the project area including the flashiness of the stream and the water quality of the runoff. 6.2 Mitigation Objectives The mitigation associated with the Triangle project is intended to: (1) Improve hydrologic functions in tributaries 0016A and 0016 by providing stormwater control for 34.10 acres of existing impervious surfaces (2) Improve water quality in tributaries 0016A and 0016 by providing water quality treatment for 34.10 acres of existing impervious surfaces (3) Improve habitat functions by increasing plant diversity, foraging and nesting habitat, overall habitat complexity, plant structure diversity and numbers, and stream shading Draft Stream Mitigation Plan BERGER/ABAM, FAPWT-04-064 I-5 — SR 161/SR 18 Triangle Improvements Project February 2009 Washington State Department of Transportation E X 111 I M T Page 41 PAGE TF (4) Create 515 linear feet of new stream channel (5) Increase in -stream and riparian habitat by removing 250 feet of existing culverts and re-establishing a stream channel. 6.3 Performance Measures and Success Standards The performance standards described below provide benchmarks for measuring achievement of the goals and objectives of the mitigation site. Mitigation activities are intended to meet these performance standards within a specified period. Performance measures and success standards for the Corrington mitigation site are contained within the Draft Wetland Mitigation Plan for the I-5 — SR 161/SR 18 Triangle Improvements Project (BERGER/ABAM 2009). 6.3.1 Interim Performance Measures (Years 1- 4) The following indicators are benchmarks for the performance of the mitigation measures in years 1 through 4. ■ Ensure that all of the proposed wildlife enhancement structures have been placed within the riparian replacement and enhancement areas and that they meet the specific size and location requirements detailed above. These include brush piles, snags and bat boxes. ■ Native, wetland (facultative and wetter) woody species (planted and volunteer) will achieve an average density of at least four plants per 100 square feet in the wetland areas of the created stream channel. ■ State -listed Class -A noxious weeds and non-native blackberries (Rubus spp.), purple loosestrife (Lythrum salicaria), Scot's broom (Cytisus scoparius), thistles (Cirsium spp.), and non-native knotweeds (Polygonum cuspidatum, P. polystachyum, P. sachalinense, and P. bohemicum) will not exceed 20% aerial cover in the created and enhanced wetlands. * Survival of 90% of riparian enhancement plantings. If dead plantings are replaced, then the performance measure will be met. a The relocated stream channel is stable, has the presence or indicators of hydrology, in -stream structures are in place and intact and the charnel has no indicators of significant erosion. 6.3.2 Success Standard (Year 5) In year 5, the success standards will include the following. a For the purpose of measuring the final success of the wildlife enhancement structures, each structure will be inventoried. The habitat brush piles may be subject to decay so measurements will not be required. All snags will be counted to ensure that all installed snags are still standing. Bat boxes will be inventoried to ensure that all installed boxes are present and intact. Draft Stream Mitigation Plan I-5 — SR 161/SR 18 Triangle Improvements Project Washington State Department of Transportation BMGMABAM, FAPWT-04-064 February 2009 EXHIBIT Page42 C - U FAGtv s Aerial cover of native, woody species will be at least 609/o in the scrub -shrub and forested communities of the created, enhanced, and restored and enhanced riparian buffer areas. • Aerial cover of native planted or appropriate volunteer plants will be at least 75% in the wetland areas of the realigned stream channel. ■ State -listed Class -A noxious weeds and non-native blackberries, purple loosestrife, Scots broom, thistles, and non-native knotweeds will not exceed 20% aerial cover in the created and enhanced riparian buffers. 7.0 REFERENCES BERGER/ABAM Engineers Inc. 2009. Draft Wetland Mitigation Plan I-5 - SR 161/SR 18 Triangle Improvements Project. Prepared for the Washington State Department of Transportation, January 2009 BERGER/ABAM Engineers Inc. 2008a. 1-5 - SR 161/SR 18 Interchange Improvements Phase 1 Hydraulics Report. Prepared for the Washington State Department of Transportation. May 2008. BERGER/ABAM Engineers Inc. 2008b. I-5 - SR 161/SR 18 Interchange Improvements Fish Evaluation Passage Report. Prepared for the Washington State Department of Transportation. February 2008. BERGER/ABAM Engineers Inc. 2008c. I-5 - SR 161/SR 18 Interchange Improvements Conceptual Wetland Mitigation Plan. Prepared for the Washington State Department of Transportation. August 2008. BERGER/ABAM Engineers Inc. 2007. I-5 - SR 161/SR 18 Triangle Improvements Fish, Vegetation, Wildlife, and Habitat Discipline Report. Prepared by CH2M Hill for the Washington State Department of Transportation. March 2007. BERGER/ABAM Engineers Inc. 2006. I-5 - SR 161/SR 18 Triangle Improvements Water Resources Discipline Report. Prepared for Washington State Department of Transportation. October 2006. King County. 1991. Executive Proposed Hylebos Creek and Lower Puget Sound Basin Plan. King County Surface Water Management. July 1991. Washington State Department of Transportation (WSDOT). 2007. Hydraulics Manual M 23-03, Engineering and Regional Operations Division, Environmental and Engineering Programs. Olympia, WA. 2007. hU://www_wsdot.wa.gov/Publications/Manuais/M23- 03.htm Washington State Department of Transportation (WSDOT). 1997. SR 161 Hylebos Creek Stream Survey. OL 2713. Prepared by Gary Davis, Biologist, Northwest Region Environmental Services. June 1997. Draft Stream Mitigation Plan I-5 — SR 161/SR 18 Triangle Improvements Project Washington State Department of Transportation BERGER/ABAK FAPWT-04-064 ��� � � �� February 2(H19 Page 43 PAGE OPT