Media filtration had been implemented for years at a 20-acre boatyard facility in Port Townsend Washington, but the treated stormwater still regularly contained copper and zinc concentrations above the permit benchmark values. With the problem identified as ineffective filtration of fine particulates, a low-cost coagulation pretreatment system was designed and installed. The coagulant employed was chitosan lactate, a passive-release gel. The chitosan lactate virtually eliminates the chance for overdosing, simplifies system operation, and greatly reduces system cost versus an active-dosed liquid coagulant system. Since addition of chitosan lactate, media filtration has effectively removed over 90 percent of influent copper and zinc, and the treated stormwater has consistently met permit benchmark values.