Summary of pollutant removal mechanisms

Summary of attenuation-removal mechanisms for primary pollutants found in stormwater runoff. Adapted from Horner, 1994 as reported in the Wisconsin Storm Water Manual Part 2.
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Mechanism	Pollutants affected	Promoted by
Sedimentation	Solids, BOD, pathogens, particulate COD, P, N, metals, synthetic organics	Low turbulence
Filtration	Solids, BOD, pathogens, particulate COD, P, N, metals, synthetic organics	Fine, dense herbaceous plants, constructed filters
Soil incorporation	All	Medium-fine texture
Precipitation	Dissolved P, metals	High alkalinity
Sorption - adsorption	Dissolved P, metals, synthetic organics	High soil Al, Fe, high soil organics (Met), circumneutral pH
Sorption - ion exchange	Dissolved metals	High soil cation exchange capacity
Oxidation	COD, petroleum hydrocarbons, synthetic organics	Aerobic conditions
Degradation - photolysis	COD, petroleum hydrocarbons, synthetic organics	Direct sunlight
Degradation - volatilization	Volatile petroleum hydrocarbons, synthetic organics	High temperature and air movement
Degradation - biological	BOD, COD, petroleum hydrocarbons, synthetic organics	High temperature and air movement
Plant metabolism	P, N, metals	High plant surface area
Pathogen die off	Pathogens	Plant excretions
Nitrification	Ammonia	Dissolved oxygen >2 mg/L, low toxicants, temperature >5-7°C, circumneutral pH
Denitrification	Nitrate, nitrite	Anaerobic, low toxicants, temperature >15°C