The Port’s Stormwater Management Program strives to handle stormwater in a manner that demonstrates best management practices. Stormwater information is divided into Airport and Maritime programs due to differences in permits and tenant responsibilities.
Oyster Shells and Stormwater
Oyster shells are being used at the Maritime port for two purposes, to increase stormwater hardness and remove copper. The hardness of stormwater is very low, as it only contacts impervious surfaces (paved areas). The copper contaminated water is harmful to fish and other aquatic species. Copper is introduced from vehicle brake pads, which produce brake dust containing the metal. Stormwater monitoring sites around high traffic volume areas along the Seattle waterfront can produce elevated levels of copper.
Samples along the Alaskan Way Viaduct were exceeding the Industrial permit benchmark for copper, at 14 parts per billion. The source of copper was discovered to be related to traffic from the Viaduct. Oyster shells have shown promising results for removing dissolved copper from water, so shells were poured directly into stormwater catch basins in the area.
The oyster shells work to filter free copper by absorption. Many factors influence this chemical process, including the level of copper present along with substrate levels of calcium or magnesium carbonate, and the acidity of the water.