Resolution_PFacilitiesAgmt2022_City of Roslyn

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1. introduction i.1. Project Purpose The City of Roslyn (City) completed a Stormwater Comprehensive Plan (Plan) in July 2014. The Plan contains structural and non-structural solutions to address stormwater conveyance and water quality problems within the City. The Capital Improvement Plan (CIP) contained within the Plan identifies various structural solutions to address conveyance issues by replacing pipes and culverts. Nonstructural solutions such as stormwater management facility inspection, public education and outreach, water quality monitoring and encouraging infiltration and low impact development are aimed at improving water quality within the region. The City received a Water Quality Grant from the Washington State Department of Ecology (Ecology) to identify ways to improve water quality within the local waterway, Crystal Creek. The goal is to identify Best Management Practices (BMPs) to provide stormwater runoff treatment for Total Suspended Solids (TSS) and provide for reduction in other pollutants within the urbanized areas of the City. The grant has two objectives: 1. Evaluate the possible implementation of stormwater retrofits to provide water quality treatment and determine the most suitable locations, methods, estimated costs, available funding, and phased approach for such retrofits in a citywide study. 2. Advance design of stormwater treatment retrofit improvements for the CIP 1 project which is a pipe rehabilitation project currently under design. 1.2. Report Purpose This report documents the citywide study to be adopted as an addendum to City of Roslyn Stormwater Comprehensive Plan. The CIP 1 treatment project will be advanced in detail design after study completion. This addendum describes the drainage basin, details of the project site, an analysis of the core elements, the alternatives considered, the design analysis, a quantification of the water quality benefit, CIP summaries, financial review of potential funding, and operation and maintenance considerations. 1.3. Design Codes and References 1.3.1. Department of Ecology The analysis will be in accordance with Ecology's Stormwater Management Manual for Eastern Washington {SWMMEW), 2019, and Ecology's Design Deliverables for Stormwater Projects with Ecology Funding, June 2018. 1.3.2. City of Roslyn This analysis will be in accordance with the City's Stormwater Regulations listed in Chapter 3 of the Plan.