Resolution_PFacilitiesAgmt2022_City of Roslyn

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2. Basin Description 2.1, General The study area lies within the Upper Yakima River watershed, Ecology Water Resource Inventory Area (WRIA) 39, where it drains into Crystal Creek and ultimately reaches the Yakima River in central Washington, near Cls Elum. The creek serves as a recreational stream, and is protected for salmonid spawning, rearing, and migration. Crystal Creek is a 303(d) listed stream and has Total Maximum Daily Load (TMDL) limits for fecal coliform, temperature, and sediment. 2.2. Historic and Existing Conditions The citywide study basin area encompasses 1,170 -acres draining to Crystal Creek as shown in the attached Exhibit 1 (Mead & Hunt, October 2019). This study basin area is composed of 50% -forested hills to the north of the City limits, and a mixed land use of low density residential, medium density residential, commercial, light industrial, and historic zones within City limits. The existing stormwater conveyance system was built as the City developed, and includes a combination of open ditches, pipes, catch basins, and culverts. The system was originally built as a combined sewer system but was later converted into dedicated storm sewers by the mid -80s. Major trunk lines were constructed as bypass systems to contain three creeks that historically flowed through the City. The City's Plan includes an inventory of the City's drainage infrastructure and proposed capital improvement projects primarily intended to address capacity issues within the City. The City generally lacks any stormwater runoff treatment. Since development of the Plan, CIP 2 project (a box culvert crossing South A Street) was completed in 2017. CIP 1 project (a bypass pipe to alleviate a bottleneck on a main storm trunk line) is currently under design development and scheduled for bidding and construction in 2022. The CEP 1 basin, a subbasin of the citywide study basin, is an 804 -acre area that currently discharges to Crystal Creek via one outfall south of East California Avenue. The CIP 1 basin is mostly forested hills with some urbanized development, including commercial, residential, light industrial, and historic uses from the City. The coal mine within the project area is no longer in use. The CIP 1 basin drains southward in a piped storm drain system along North First Street before it discharges into Crystal Creek. 2.3. Proposed Conditions The citywide study does not propose any changes to the land use, basin delineations, soils or water bodies. The proposed retrofits for stormwater treatment in the study area will capture stormwater flow from existing topography before flowing through underdrains and into the existing storm drain system.