Engineered infiltration systems for urban stormwater reclamation

Urban stormwater contains a variety of contaminants that can adversely impact receiving waters. Contaminants of greatest concern include compounds derived from paving materials and automobile tires, biocides, and pathogens. Low-impact development systems built to manage urban stormwater often utilize some form of engineered infiltration or subsurface filtration to reduce the volume of runoff leaving a developed site. Use of infiltration techniques without proper consideration of contaminants in stormwater risks further degradation of urban ecosystems and water resources. Although engineered infiltration systems also have the capacity to remove contaminants from stormwater, the potential of these systems has not yet been fully exploited or optimized. With improved designs based on known mechanisms of contaminant removal, engineered infiltration has the potential to provide reliable treatment of urban stormwater, resulting in a water resource that is safe for aquifer recharge or urban stream restoration. This article discusses chemical and biological contaminants of concern in urban stormwater and the mechanisms by which they are removed during infiltration through porous media systems, including filtration, sorption, and chemical and biological transformation. Three strategies have been identified as opportunities to more effectively optimize treatment of stormwater: (1) choice of infiltration media; (2) manipulation of system hydraulic behavior; and (3) manipulation of redox conditions. Novel techniques to apply these strategies and topics requiring further research are also discussed.