The success of engineered systems to capture stormwater runoff from Seattle’s Aurora Avenue Bridge has spurred construction of additional measures that proponents say will increase total filtering capacity by another two million gallons per year.
Constructed in 1929, the cantilever and truss bridge rises nearly 170 feet above the Lake Washington Ship Canal, which connects Lake Union to Puget Sound. Stormwater runoff from the bridge has long carried untreated oil, deicing chemicals, metals and other materials into the waterway, compromising the health of salmon and the orcas that feed on them. The Nature Conservancy reports that stormwater runoff samples for the Aurora Bridge contained a median total suspended solids (TSS) level of 567 mg/L, well above the National Stormwater Quality Database baseline of 99 mg/L.