Resolution_PFacilitiesAgmt2022_City of Roslyn

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3. Project Site Description 3.9, Project Limits The project site for the stormwater retrofit study area is intended to capture the urbanized areas within the Stormwater Retrofit Study Area shown in Exhibit 1 and Exhibit 2. The project site is a 270 -acre area of developed lands within the City that discharge to Crystal Creels, and consists of commercial, residential, light industrial, public facilities and historic uses. The drainage subbasins delineated in the Plan were carried forward for this analysis. The potential locations identified for stormwater retrofits were reduced to exclude the restricted buffer area per Policy H2.5 of the City of Roslyn, which specifies that "all lots within 300 feet of wetlands shall be 50 acres or larger. No building or development is permitted within 300 feet of wetlands." This area was further reduced to remove the unsewered areas of the City. The resultant Treatment Assessment Area measures approximately 152 acres and is shown in Exhibit 2. The CIP 1 Treatment Assessment Area is shown in the attached Exhibit 2 as the urbanized tributary area for the CIP 1 treatment project and measures approximately 45 acres. The ClP 1 treatment project will advance design of the treatment facilities within the CIP 1 Treatment Assessment Area. Final design and construction will be done under separate grant funding. The CIP 1 Treatment Assessment Area drainage subbasins were subdivided into smaller subbasins to aid in a more detailed analysis for design advancement and quantification of the water quality benefit. The drainage areas and existing impervious areas are listed in Appendix A for each subbasin shown in Exhibit 2. 3.2. Project Site Conditions The land use is predominantly urbanized, including commercial, residential, light industrial, and historic uses from the City. The site generally slopes from northwest to southeast towards Crystal Creek. There are significant elevation differences throughout the City. The tax parcels (and public right-of-way) were obtained from the Kittitas County COMPAS database. The topographic contours were obtained from the Washington State UDAR portal, Kittitas County FEMA Study conducted in 2011 ntts:l/lido ortal.dnr wa. ovX47.23423:-124.9957 :15). There are wetlands to the west and southeast of the Treatment Assessment Area. Wetlands exist south of Roslyn Pioneer Park, north of Whitehead Road where Crystal Creek crosses the road, and south of Whitehead Road. The wetland boundaries and associated layers were obtained from the Plan. The soils within the project site are mostly Roslyn ashy sandy loam with a Hydrologic Soil Group of B, and Teanaway ashy loam with a Hydrologic Soil Group of C. There are also some dumps and mine sediment with a Hydrologic Soil Group of D according to the Gridded Soil Survey (gSSURGO) Database. The climate is heavily influenced by the adjacent mountain ranges and elevation. Precipitation is higher in the winter than the summer. The Plan provides more details regarding average monthly