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21-104125-Critical Areas Report-9-28-22WETLAND DELINEATION • MITIGATION DESIGN • COMPLIANCE MONITORING September 21, 2022 Project No. 20030 VSM Attention: Sikander Sekhon PO Box 1226 Kent, Washington 98035 Regarding: Critical Area Report: Wetlands and Streams Proposed VSM Plat - Federal Way, Washington Sikander, 1.0  INTRODUCTION  This critical area report has been prepared for the proposed VSM Plat located in Federal Way, Washington. The project includes the subdivision of two existing residential properties into eleven residential lots. Plat improvements encroach the outer limits of a Type Ns stream buffer and several Category IV wetland buffers. To offset proposed buffer impacts 10,831 sf of combined wetland and stream buffer enhancement is proposed. This report has been prepared per Federal Way Revised Code (FWRC) 19.148.080 to address wetland and stream buffer impacts and should be reviewed in combination with the mitigation plan entitled “Wetland and Stream Buffer Mitigation Plan – VSM Plat” dated September 21, 2022 and all subsequent revisions. 2.0 REPORT AUTHORIZATION, SCOPE OF SERVICES, & QUALIFICATIONS  Authorization to prepare this report was granted by Sikander Sekhon on August 29, 2022. This report has been prepared per the critical area reporting requirements established in FWRC 19.148.080 to describe existing wetland and stream conditions as well as proposed impacts and buffer enhancements. The qualifications I maintain to complete this report include a Bachelor of Science degree in Environmental Science, certification as a Professional Wetland Scientist (PWS), and nearly 24 years of environmental consulting experience within the Puget Sound area of Washington State. 3.0 PROJECT SITE & LANDSCAPE SETTING  The project site includes the developed residential properties located at 2625 and 2641 S 298th Street in Federal Way, Washington. The sites exist within the southeast quarter of Section 4, Township 21 North, Range 4 East, W.M. King County tax parcel numbers for the two properties are 768380-0280 and 768380- 0290. The project site has a total area of 177,756 SF (4.08 AC) and compromises flat to gently sloping land. Two primary residential structures and several accessory residential structures exist within the site. PO Box 1721 Issaquah, Washington 98027 (425) 677-7166 www.evergreenarc.com Critical Area Report:  Wetlands and Streams  Proposed VSN Plat – Federal Way, Washington  Page 2  Vegetation throughout the site is predominantly grass with scattered trees. Land use surrounding the site is principally single-family residential, though Wildwood Elementary School is located southwest of project site and Laurelwood Park is located northwest of the site. 4.0 CRITICAL AREAS  A Type Ns stream and four Category IV wetlands exist in a low lying area located within the western portion of the project site. Wetland and stream conditions were assessed in January 2021 and summarized in a “Critical Area Delineation and Rating Report” dated March 15, 2021. Delineated wetland and stream limits were surveyed by Encompass Engineering and Surveying and are shown on applicable engineering and design drawings prepared for the VSM plat. The Type Ns stream is a low gradient linear aquatic feature that measures an average of three feet wide by six inches deep. The stream drains to the northwest across the project site. Stream flow is derived from the concentration of stormwater generated by impervious surfaces in the residential subdivision located south of the project site. A 35 foot wide buffer extends away from the ordinary high water mark (OHWM) of the stream and a 15 foot setback is required from the outer limits of the stream buffer for buildings and other structures. Four Category IV wetlands exist within shallow landforms along the Type Ns stream. Vegetation within the wetlands is dominated by tall fescue (Festuca arundinacea, FAC) with occasional creeping jenny (Lysimachia nummularia, FACW), common rush (Juncus effusus, FACW), bird’s-foot trefoil (Lotus corniculatus, FAC), and creeping buttercup (Ranunculus repens, FACW). The wetlands were assigned a Category IV rating based on a total score of 15 that they received for functions. Category IV wetlands have the lowest level of functions because they are often heavily disturbed or otherwise significantly altered from a natural condition (Hruby 2014). A 50 foot buffer extends away from the delineated limits of each wetland and a 15 foot setback is required from the outer limits of each wetland buffer for buildings and other structures. 5.0 PROPOSED PROJECT  The proposed project includes clearing, grading, and platting of the project site to accommodate the construction of eleven new single-family lots, a stormwater tract, a critical area tract, a public access road, and utilities. New residential lots will be consolidated in the central and eastern portion of the site. A new access road as well as water and sewer services will extend south from S 298th Street to serve the new residential lots. The existing residence on parcel 768380-0280 will be retained within Lot 1. Ten new single-family homes will be constructed on the remaining lots. Street frontage improvements will occur along S 298th Street, though frontage improvements located in the northwest corner of the site have been included with the proposed project in concept only. The plat developer plans to apply for an exemption or variance during final engineering design to eliminate the frontage improvements in the northwest corner of the site. Stormwater generated by new impervious surfaces within the plat (i.e., rooftops, sidewalks, driveways and roads) will be routed to a new stormwater pond located near the southern property line in the central Critical Area Report:  Wetlands and Streams  Proposed VSN Plat – Federal Way, Washington  Page 3  portion of the plat. The detention pond will be bordered by the critical area tract to the west, Lot 4 to the north, and Lot 5 to the east. The pond will provide a total detention volume of 34,050 CF. A four foot by twelve foot Oldcastle BioPod water quality vault will be located upstream of the detention pond to provide enhanced basic water quality treatment of stormwater that is directed towards the pond. The pond will outlet via a control structure (dispersion trench) located west of Lot 3 and Lot 4. The dispersion trench and related piping will be located within an easement. The proposed stormwater pond and outlet structure encroach the outer portion of the Type Ns stream and Category IV wetland buffers. 6.0 CRITICAL AREA IMPACTS  Unavoidable critical area impacts related tot the proposed project include the construction of stormwater infrastructure along the outer portion of a Type Ns stream buffer and the outer portion of several Category IV wetland buffers. Work will include excavation and grading to construct the stormwater pond, the stormwater pond emergency overflow, and the related dispersion trench and piping. Total buffer impact area is 2,305 sf, which includes overlapping wetland and stream buffers. Wetland buffer impact is 2,186 sf and results in a localized reduction of the standard 50 ft wetland buffer to a minimum width of 37.5 feet. Stream buffer impact is 505 sf and results in a localized reduction of the 35 foot standard stream buffer to a minimum width of 25.6 feet. Currently, the buffers support gently to modestly sloping topography vegetated with a mixture of pasture grasses and occasional herbaceous weeds. FWRC 19.145.130 requires an applicant to apply sequential measures (“mitigation sequencing”) to reduce, avoid, and mitigate impacts to critical area buffers. The location, size, and type of the proposed stormwater control infrastructure has been designed per the latest edition of the King County Surface Water Design Manual and the City of Federal Way’s Addendum to the King County Surface Water Design Manual. The location and type of infrastructure is based on engineering and design considerations such as topography, soil conditions, hydraulics, water quality and detentions standards, and proximity to plat development. The proposed stormwater control infrastructure completely avoids work within the on-site wetlands and the stream and buffer impacts have been minimized by consolidating the proposed infrastructure along the outer portion of the related buffers. The proposed infrastructure will be constructed using high quality/low maintenance materials to ensure sustainability over time. A geotechnical assessment by Earth Solutions NW, LLC (2022) determined that alternatives to the current design such as infiltration were infeasible or potentially problematic due to existing soil conditions. 7.0 PROPOSED MITIGATION  A detailed mitigation plan has been prepared for the proposed project. The primary purpose of the plan is to describe the proposed buffer enhancements necessary to offset unavoidable buffer impacts. Specific mitigation goals, objectives, and performance standards are detailed on the mitigation plan. The overall goal and objective of the mitigation is to enhance ecological functioning within retained wetland and stream buffers located west of proposed plat development. The performance standards established on the mitigation plan assess the specific physical attributes of the enhanced buffers to ensure the completed work achieves the mitigation plan goals and objectives. Proposed mitigation for wetland and stream buffer impacts includes the installation of dense native Critical Area Report:  Wetlands and Streams  Proposed VSN Plat – Federal Way, Washington  Page 4  plantings within 10,831 sf of retained overlapping wetland and stream buffer located west of proposed buffer impacts. Given the combined proposed impact area of 2,305 sf, the resulting mitigation ratio is 4.71:1 (area of mitigation:area of impact). The mitigation area currently includes modestly sloping topography vegetated with a mix of pasture grasses and occasional herbaceous weeds. Proposed native plantings include a mix of trees and shrubs installed per industry standards of nine feet on-center spacing for trees and six feet on-center spacing for shrubs. The resulting net on-center spacing for the enhancement plantings is approximately five feet on- center. The proposed buffer enhancements ensure a diverse assemblage of native plants and high native plant coverage. It is expected that over time, the plantings will develop into a native plant community typical of the Puget Sound area of the western hemlock forest zone described by Franklin & Dyrness (1988), though modified slightly to address the specific environmental conditions the currently exist on the site. The proposed plantings will increase the distribution and abundance of native vegetation within on-site buffers and will provide opportunities for ecological functioning that currently either does not exist or is otherwise limited within on-site buffers. Critical area signage and fencing will be installed at the reduced buffer limits along the limits of plat improvements. The proposed mitigation will be completed by the plat developer prior to final plat approval. A maintenance and monitoring plan is included on the mitigation plan. This work includes specific inspections and oversight by a qualified professional during construction as well as a detailed maintenance and monitoring program. The maintenance program is designed to promote the successful establishment and vigorous growth of the installed plants. The monitoring program is designed to effectively evaluate the buffer enhancement and assess performance of the mitigation relative to the standards established for the project. A detailed contingency planning process is also included on the mitigation plan. Should monitoring reveal that the performance standards are not met, appropriate contingency plans will be developed by the landowner to address any deficiency. 8.0 WETLAND AND STREAM BUFFER FUNCTIONAL ANALYSIS  FWRC 19.145.330 requires that an applicant requesting stream buffer intrusions to demonstrate that the remaining and enhanced stream buffer will function at an equivalent or higher level than the standard buffer. Similarly, FWRC 19.145.440(6) requires that an applicant proposing wetland buffer reduction with enhancement clearly substantiate that the enhanced buffer will improve and provide additional protection of wetland functions and values. In both cases, buffer functions to be assessed include habitat, water quality, stormwater retention, groundwater recharge, and erosion protection. This report section describes how the proposed buffer mitigation satisfies the functional standards established in FWRC 19.145.330 and FWRC 19.145.440(6). For simplicity, the higher standard of “improvement and additional protection” is applied to the assessment. Critical Area Report:  Wetlands and Streams  Proposed VSN Plat – Federal Way, Washington  Page 5  8.1 Habitat Habitat functions are the ability of a buffer to provide space or conditions for reproduction, resting, hiding, and migration as well as food production and delivery for riparian and wetland-dependent birds, invertebrates, mammals, amphibians, and native fish. Suitable habitat for a wide range of native fauna can be provided by a broad range of vegetation structures, high plant species richness, and the interspersion of different habitat types (McMillan 2000; Sheldon et. al 2005). Existing habitat function within on-site wetland and stream buffers is extremely limited because existing vegetation is limited to a simple plant community comprising pasture grasses and herbaceous weeds. The proposed mitigation improves and provides additional protection to habitat functions by requiring the installation of dense native plantings comprising a diversity of tree and shrub species. The proposed vegetation will develop into multi-layered plant community that will provide valuable habitat niches and connectivity pathways for wetland/riparian dependent wildlife species. 8.2 Water Quality Water quality functions are the ability of a wetland or stream buffer to filter and prevent sediment and nutrients (primarily nitrogen and phosphorus) from entering a wetland or stream. Ideal filtering conditions include gradual slopes, organic soils, and dense forest or grass vegetated areas with high surface roughness coefficients (Sheldon et. al 2005; McMillan 2000; Mitsch and Goesselink 2000). Existing water quality functions within on-site buffers are limited due to sloping landform and a simple plant community comprising pasture grasses and herbaceous weeds of variable densities. The proposed mitigation improves and provides additional protection to water quality functions by requiring the installation of native plants, that once established, will provide the resilient vegetative structure needed to physically filter sediments and increase the ability of the buffer to trap pollutants through biological uptake. 8.3 Stormwater Retention Stormwater retention functions are the ability of the buffer to trap and permanently store surface water runoff. Stormwater retention functions require specific soil and topographic conditions to be present. Neither of the required conditions exist within on-site buffers. The existing buffer slopes towards the stream and wetlands and exists within mapped Alderwood gravelly sandy loam, 0 to 8 percent slopes (AgB) and Arnets, Alderwood material, 6 to 15 percent slopes (AmC) soil types. Both soil types are classified as moderately well drained soils. Test pit #4 logged by Earth Solutions NW, LLC (2022) just outside of the standard stream/wetland buffer documented the presence of a thin topsoil overlying thick silty sand with gravel. The proposed project maintains existing soil and topographic conditions. It is not possible to improve or provide additional protection of stormwater retention functions without degrading or negatively affecting other buffer functions. 8.4 Groundwater Recharge Groundwater recharge is the ability of a buffer to detaining and infiltrating surface water within buffer areas. Test pit #4 logged by Earth Solutions NW, LLC (2022) just outside of the standard stream/wetland buffer documents minimal root penetration within the upper one foot of existing soil near the on-site buffer. Existing groundwater recharge functions within on-site buffers are limited Critical Area Report:  Wetlands and Streams  Proposed VSN Plat – Federal Way, Washington  Page 6  due to a sloping landform and the presence of a simple herbaceous plant community of variable density that presents limited root penetration into existing soils. The proposed mitigation improves and provides additional protection to groundwater recharge functions by requiring the installation of dense native plantings with roots that will penetrate buffer soils to a depth greater than existing the existing pasture grasses and herbaceous weeds. The density of proposed plantings combined with the increase depth of root penetration will increase the ability of the buffer to infiltrate surface water. 8.5 Erosion Protection Erosion protection is the ability of a buffer to limit the effects of erosion. The existing buffer is vegetated by a variable density grass and herbaceous weed plant community. The proposed project improves and provides additional protection to erosion protection functions by providing additional physical structure (i.e., trees and shrubs) that will shield the soil surface from precipitation as well as bind soil particles with the deep penetrating roots. 9.0  REGULATORY COMPLIANCE   9.1 Intrusion into Stream Buffers (FWRC 19.145.330) The proposed project requires 505 sf of stream buffer impact and results in a localized reduction of the 35 foot standard stream buffer to a minimum width of 25.6 feet. FWRC 19.145.330 requires review of stream buffer intrusions by the City of Federal Way using Process III subject to the following decisional criteria: 1. Stream buffer intrusions may be permitted with a buffer enhancement plan. The plan shall provide an assessment of the following existing functions and conditions of the buffer and the effects of the proposed buffer modification on those functions: (a) habitat; (b) water quality; (c) stormwater retention capabilities; (d) groundwater recharge; and (e) erosion protection. See report section 8.0. 2. The City of Federal Way may approve a stream buffer intrusion based on the following criteria: (a) It will not adversely affect water quality. The project conforms to this standard. The proposed stream buffer intrusion will not adversely affect water quality because the proposed stormwater control infrastructure has been designed per current engineering standards and the proposed buffer mitigation provides resilient vegetative structure that increases the ability of the buffer to physically filter sediments and trap pollutants. (b) It will not adversely affect the existing quality of wildlife habitat within the stream or buffer area. Critical Area Report:  Wetlands and Streams  Proposed VSN Plat – Federal Way, Washington  Page 7  The project conforms to this standard. The proposed stream buffer intrusion will not adversely affect the existing quality of wildlife habitat within on-site buffers because the proposed buffer impacts will occur along the outer portion of the buffer within areas of low quality habitat and the proposed mitigation requires the installation of dense native plantings within retained buffer areas. (c) It will not adversely affect drainage or stormwater retention capabilities. The project conforms to this standard. The proposed stream buffer intrusion will not adversely affect drainage capabilities because the proposed stormwater control infrastructure has been designed to match pre-development stormwater characteristics. The proposed project will not adversely affect stormwater retention capabilities because neither the soil nor topographic conditions exist within on-site buffers to provide appreciable stormwater retention capabilities under existing or proposed conditions. (d) It will not lead to unstable earth conditions nor create erosion hazards. The project conforms to this standard. The proposed stream buffer intrusion will not lead to unstable earth conditions nor create erosion hazards because appropriate temporary erosion and sediment control best management practices will be employed during construction and affected areas will be permanently stabilized following construction. In addition, proposed native plantings within retained buffer areas will provide the physical structure to shield the soil surface from precipitation and bind soil particles with deep penetrating roots typical of native plant species. (e) It will not be materially detrimental to any other property in the area of the subject property nor the city as a whole. The project conforms to this standard. The proposed stream buffer intrusion will not be materially detrimental to any other property in the area of the subject property nor the City of Federal Way as a whole because the purpose of the proposed buffer impacts is to mitigate the effects of stormwater generated by the proposed plat. The proposed stormwater control infrastructure has been designed to match pre-development stormwater discharge durations and rates and a downstream analysis documented no existing problems or limitations within the affected drainage subbasin. The proposed project will preserve and protect the Type Ns stream and related buffer within a critical area tract. The proposed stream buffer mitigation has been designed to offset proposed buffer impacts by enhancing the ecological functioning of retained buffers. (f) It Is necessary for reasonable development of the subject property. The project conforms to this standard. The proposed stream buffer intrusion is necessary for reasonable development of the subject property. Proposed site development has been consolidated into the eastern and central portion of the site. The location and type of Critical Area Report:  Wetlands and Streams  Proposed VSN Plat – Federal Way, Washington  Page 8  stormwater control infrastructure is based on engineering and design considerations such as topography, soil conditions, hydraulics, water quality and detentions standards, and proximity to plat development. The proposed stormwater control infrastructure completely avoids work within the on-site wetlands and the stream by locating the infrastructure at the outer limits of each buffer and impacts have been minimized by configuring the infrastructure along the outer limits of the buffer. A geotechnical assessment by Earth Solutions NW, LLC (2022) determined that alternatives to the current design such as infiltration were infeasible or potentially problematic due to existing soil conditions. 9.2 Development within Wetland Buffers (FWRC 19.145.440.[6]) The proposed project requires 2,298 sf of wetland buffer permanent impacts and results in localized reduction of the standard 50 ft wetland buffer to a minimum width of 37.5 feet. FWRC 19.145.440(6) requires review of wetland buffer reductions with enhancement by the City of Federal Way using Process III subject to the following decisional criteria: (a) It will not adversely affect water quality. The project conforms to this standard. The proposed wetland buffer reduction will not adversely affect water quality because the proposed stormwater control infrastructure has been designed per current engineering standards and the proposed buffer mitigation provides resilient vegetative structure that increases the ability of the buffer to physically filter sediments and trap pollutants. (b) It will not adversely affect the existing quality of the wetland or buffer wildlife habitat. The project conforms to this standard. The proposed wetland buffer reduction will not adversely affect the existing quality of the wetland or buffer wildlife habitat because the proposed buffer impacts will occur along the outer portion of the buffer within areas of low quality habitat and the proposed mitigation requires the installation of dense native plantings within retained buffer areas. (c) It will not adversely affect drainage or stormwater retention capabilities. The project conforms to this standard. The proposed wetland buffer reduction will not adversely affect drainage capabilities because the proposed stormwater control infrastructure has been designed to match pre-development stormwater characteristics. The proposed project will not adversely affect stormwater retention capabilities because neither the soil nor topographic conditions exist within on-site buffers to provide appreciable stormwater retention capabilities under existing or proposed conditions. (d) It will not lead to unstable earth conditions nor create erosion hazards. The project conforms to this standard. The proposed wetland buffer reduction will not lead to unstable earth conditions nor create erosion hazards because appropriate temporary erosion and Critical Area Report:  Wetlands and Streams  Proposed VSN Plat – Federal Way, Washington  Page 9  sediment control best management practices will be employed during construction and the affected areas will be permanently stabilized following construction. In addition, proposed native plantings within retained buffer areas will provide the physical structure to shield the soil surface from precipitation as well as the ability to bind soil particles with deep penetrating roots typical of native plant species. (e) It will not be materially detrimental to any other property or the city as a whole. The project conforms to this standard. The proposed wetland buffer reduction will not be materially detrimental to any other property in the area of the subject property nor the City of Federal Way as a whole because the purpose of the proposed buffer impacts is to mitigate the effects of stormwater generated by the proposed plat. The proposed stormwater control infrastructure has been designed to match pre-development stormwater discharge durations and rates and a downstream analysis found no existing and potential drainage problems within the affected drainage subbasin. The proposed project will preserve and protect the existing Category IV wetlands and related buffers within a critical area tract. The proposed wetland buffer mitigation has been designed to offset proposed buffer impacts by enhancing the ecological functioning of retained buffers. (f) All exposed areas are stabilized with native vegetation, as appropriate. The project conforms to this standard. The proposed wetland buffer mitigation includes the installation of dense native vegetation. 10.0  CLOSURE   The proposed VSM Plat includes subdivision of two existing residential properties into eleven residential lots. Plat improvements encroach the outer limits of a Type Ns stream buffer and three Category IV wetland buffers. To offset proposed buffer impacts 10,831 sf of combined wetland and stream buffer enhancement is proposed. The project conforms to the buffer intrusion and reduction decisional criteria established in FWRC 19.145.330 and FWRC 19.145.440(6). Within the limitations of scope, schedule, and budget, the critical area consulting services summarized in this report conform to the generally accepted standard of care in effect at the time the work was conducted. No other warranty, express or implied, is made. The purpose of the work described in this report is to describe site and impacts conditions per the City of Federal Way critical area regulations in effect at the time of report preparation. All opinions presented in this report should be considered preliminary until reviewed and confirmed by the City of Federal Way. I trust that this report meets your present needs. If you have any questions regarding the information presented in this report or require additional assistance with this project, please do not hesitate to call me at (425) 864-3244 or email me at psuper@evergreenarc.com. Critical Area Report:  Wetlands and Streams  Proposed VSN Plat – Federal Way, Washington  Page 10  Sincerely, EVERGREEN AQUATIC RESOURCE CONSULTANTS, LLC Issaquah, Washington Peter P. Super Professional Wetland Scientist Attachments: 1. Photographs of Buffer Reduction Area 11.0  REFERENCES   Castelle, A.J., C. Conolly, M. Emers, E.D. Metz, S. Meyer, M. Witter, S. Mauermann, T. Erickson, S.S. Cooke. (1992). Wetland Buffers: Use and Effectiveness. Adolfson Associates, Inc. Shorelands and Coastal Zone Management Program, Washington Department of Ecology, Olympia. Pub. No. 92-10. Earth Solutions NW, LLC. 2022. Geotechnical Engineering Study: VSM Short Plat. Prepared for VSM. January 13, 2022. Encompass Engineering & Surveying. 2021. Preliminary Technical Information Report: City of Federal Way for VSM Plat. Prepared for Sikander Sekhon. October 4, 2021. Hruby, T. (2014). Washington State Wetland Rating System for Western Washington: 2014 Update. Washington State Department of Ecology Publication #14-06-029. Olympia, Washington: Washington State Department of Ecology. King County. (2004). Best Available Science: Volume I – A Review of Scientific Literature. King County Executive Report. Department of Natural Resources Division: Water and Land Resources Division. February 2004. McMilan. A. (2000). The Science of Wetland Buffers and Its Implication for the Management of Wetlands. MS. Evergreen State Collage, Olympia, Washington. August 2000. Mitsch, W.J. and J.G. Gosselink. (2000). Wetlands: Third Edition. John Wiley & Sons, Inc. June 2000 Sheldon, D., T. Hruby, P. Johnson, K. Harper, A. McMillan, T. Granger, S. Stanley, and E. Stockdale. (2005). Wetlands in Washington State - Volume 1: A Synthesis of the Science. Washington State Department of Ecology. Publication #05-06-006. Olympia, WA. Critical Area Report:  Wetlands and Streams  Proposed VSN Plat – Federal Way, Washington  Page 11  JANUARY 15, 2021 PHOTO SHOWING THE SOUTHERN PORTION OF WETLAND/STREAM BUFFER NEAR PROPOSED BUFFER INTRUSION. Critical Area Report:  Wetlands and Streams  Proposed VSN Plat – Federal Way, Washington  Page 12  JANUARY 15, 2021 PHOTO SHOWING CENTRAL/NORTHERN PORTION OF WETLAND/STREAM BUFFER NEAR PROPOSED BUFFER INTRUSION.