Stormwater Analysis Helps Reduce Seattle’s Wastewater Contaminants

Overview

By sampling and analyzing river sediments near outfall pipes, water and solids in storm drain structures upstream of the outfall pipes, and upland industrial sources of contaminants including paint, caulking material, and surface debris, SAIC is helping the Washington State Department of Ecology (Ecology) understand how upland industrial sources and stormwater contribute to contamination of river sediments . With scientists from a broad range of disciplines, SAIC has demonstrated the ability to analyze and synthesize complex and diverse types of data.

“SAIC has provided excellent service in working with Ecology
and the site operator in designing, installing, and operating flow-weighted stormwater sampling equipment on an
accelerated schedule.”
- Mark Edens, Ecology

Ecology selected SAIC to assist with identification and control of potential sources of contaminants to the Lower Duwamish Waterway Superfund Site, and to develop source control actions designed to minimize the potential for sediment recontamination following cleanup and remediation of the Waterway. SAIC has collected outfall sediment samples at 162 locations near 84 stormwater outfalls, and has collected whole water, filtered suspended solids, sediment trap solids, centrifuged solids, and grab solids samples in representative storm drain systems discharging to these outfalls.

At one large industrial property that is a major contributor of polychlorinated biphenyls (PCBs) to the Lower Duwamish Waterway, SAIC sampled stormwater and storm drain solids during storm event and base flow conditions over three years to assess contaminant loading to the waterway, evaluate the potential for sediment recontamination, and to determine the effectiveness of stormwater treatment and other source controls implemented at the site.

SAIC has also sampled potential sources of these contaminants, including PCBs in building materials (paint and building caulk), surface debris, soil, groundwater, and seeps. We are currently evaluating the significance of air deposition as a pathway for transport of contaminants to river sediments, and are helping to identify potential contaminant sources in the Green River drainage basin, upstream of the Lower Duwamish Waterway.

SAIC’s ability to synthesize and evaluate large volumes of complex and interrelated data has helped Ecology to develop a better understanding of the relationship between contaminants in stormwater and river sediments, and how to reduce the potential for recontamination of Lower Duwamish Waterway sediments after remediation.