Evaluation of Constructed Wetland and Retention Pond BMPs for Attenuating Microbial Contaminants in Urban Stormwater Runoff

The U.S. Environmental Protection Agency strives to protect human health, ensure the safety of drinking and recreational waters, support economic and recreational activities, and provide healthy habitat for fish, plants, and wildlife. To accomplish these objectives, the Agency emphasizes restoring and maintaining our oceans, watersheds, and their aquatic ecosystems. Urbanization results in more impervious areas that cause larger quantities of stormwater runoff. This runoff can contribute significant amounts of pollutants (e.g., litter, oils, microorganisms, sediments, nutrients, organic matter, and heavy metals) to receiving waters.To improve water quality in urban and suburban areas, watershed managers often incorporate structural best management practices (BMPs) to remove or reduce pollutants contained in stormwater runoff. In this project, constructed wetlands and retention ponds were evaluated for reducing microbial concentrations from urban stormwater runoff. Several studies have looked at the capabilities of these BMPs to reduce pollutant concentrations and loadings. Few studies, however, have focused on the internal mechanisms occurring in these BMPs and fewer yet on using these BMPs for treating microbial pollutants.Preliminary results indicate both types of BMPs can lower microbial concentrations from urban stormwater runoff. Retention ponds had greater removal rates for enterococci and E. coli in June and September sampling events. However, further reduction may be limited by irreducible concentrations contained in the urban stormwater runoff and/or the sediments entering into or existing within the BMPs. The disparity in results may be due to light, temperature, and predation differences between the two treatments.