On average, 45% of the phosphorus load and up to 50% of the metal load is transported through stormwater treatment practices to downstream receiving waters as dissolved contaminants. Metals of primary concern (based on toxicity and occurrence) in stormwater are cadmium, copper, and zinc. Because dissolved nutrients and metals have a higher bioavailability factor than particulate forms, removing particulate fractions from stormwater only minimally reduces the bioavailability of pollutants that reach downstream receiving water bodies. Physical treatment processes such as sedimentation and filtration cannot capture the dissolved fraction and therefore advanced treatment is required to capture the dissolved fraction.
Fortunately, research has shown that there are cost-effective methods for capturing the dissolved fraction of phosphorus and metals. Steel and iron have been shown to be effective at removing dissolved metals and dissolved phosphorus from water. Various applications using iron or other additives from actual field installations to an infiltration basin, filtration trenches, filtration berms, filtration check dams, and rain gardens that are designed to remove dissolved metals and phosphorus will be presented and data from these installations will show how these practices significantly capture the dissolved pollutant fraction.