Monitoring and Modeling the Effects of Stormwater Source Controls on Sediment Quality in Tacoma, Washington

Following the successful Superfund sediment remediation in the Thea Foss Waterway (2006), the City of Tacoma manages sediment recontamination along its downtown waterfront using a multi-faceted program which includes sediment/stormwater monitoring; an EPA-supported sediment recontamination model (Water Quality Analysis Simulation Program); source control; and a GIS-based pollutant loading model (Hydrologic Simulation Program Fortran).The City's stormwater source control program has resulted in statistically significant reductions of many chemicals in stormwater based on the multi-decade monitoring. In particular, it has been demonstrated that system-wide storm line cleaning was successful at removing historical contamination, resulting in statistically significant reductions in polycyclic aromatic hydrocarbons and bis(2-ethylhexyl)phthalate concentrations at the outfalls. For ongoing contaminant contributions, a GIS-based pollutant loading model will be used to identify areas that contribute disproportionately to stormwater pollution, to focus and recommend costeffective source control investments and to compare the cost-effectiveness of treatment and management practices for reducing pollutant loads.