SR-520 Bridge Stormwater Monitoring

Aspect is monitoring flow and water quality at three locations on the SR-520 Floating Bridge to verify if metals concentrations in stormwater runoff from the bridge deck are at or below those anticipated in stormwater models for the AKART report prepared for the bridge construction project. Aspect designed and installed three custom flow and water quality monitoring stations on the SR-520 bridge. Each station uses a custom weir box, pressure transducer, and a telemetered datalogger paired with an Isco 6712 sampler to collect continuous flow data and flow-weighted composite samples. In addition, Aspect provided content and comments on the Ecology-approved QAPP. Aspect will monitor each site for three years and will calculate rainfall-runoff curves for each site and summarize project results in a brief report. Aspect maintains each site on a monthly basis and reviews continuous data weekly. Results of the flow and water-quality sampling will be used to verify that metals concentrations in runoff entering Lake Washington from the bridge are at or below the levels modelled during the AKART analysis.