Development of An Empirical Water Quality Model for Stormwater Based on Watershed Land Use in Puget Sound

Abstract : The Sinclair and Dyes Inlet watershed is located on the west side of Puget Sound in Kitsap County, Washington, U.S.A. (Figure 1). The Puget Sound Naval Shipyard (PSNS), U.S Environmental Protection Agency (USEPA), the Washington State Department of Ecology (WA-DOE), Kitsap County, City of Bremerton, City of Bainbridge Island, City of Port Orchard, Suquamish Tribe and other stakeholders have joined in a cooperative effort to evaluate water-quality conditions in the Sinclair-Dyes Inlet watershed and correct identified problems. A major focus of this project, known as Project ENVVEST, is to develop Water Quality Improvement Projects (also known as Total Maximum Daily Loads - TMDLs) for constituents listed on the 303(d) list within the Sinclair and Dyes Inlet watershed (Johnston 2004). Segments within the Sinclair and Dyes Inlet watershed were listed on the State of Washington's 1998 303(d) because of fecal coliform contamination in marine water, metals in sediment and fish tissue, and organics in sediment and fish tissue (WA-DOE 2003). Stormwater loading was identified by ENVVEST as one potential source of sediment contamination, which lacked sufficient data for a contaminant mass balance calculation for the watershed. This paper summarizes the development of an empirical model for estimating contaminant concentrations in all streams and outfalls discharging into Sinclair and Dyes Inlets. The model is based on current watershed land use and data collected during 18 storm events, and wet/dry season baseflow conditions between November 2002 and May 2005. Stream pollutant concentrations along with estimates for stormwater outfalls and surface runoff will be used in estimating the loading and ultimately in establishing a Water Cleanup Plan (TMDL) for the Sinclair-Dyes Inlet watershed.