Indicator Bacteria Removal by Bioretention in North Carolina

Abstract

Stormwater runoff is a transport mechanism for indicator bacteria to receiving waters, resulting in an increased risk to public health through consumption of contaminated shellfish or ingestion by swimmers. The resulting economic and public safety concerns are common throughout the United States, particularly in coastal areas. Urban stormwater is commonly treated by stormwater Best Management Practices (BMPs), each of which provides some combination of natural treatment mechanisms and fosters certain environmental conditions. Although BMPs have been studied in detail for many pollutants, there is still a relatively limited understanding of their ability to remove or inactivate indicator bacteria. The North Carolina State University Biological and Agricultural Engineering Department evaluated bioretention areas in Wilmington, NC, to evaluate their efficiency with respect to indicator bacteria removal. Data collected from these studies indicates that positive removal of indicator bacteria is possible in bioretention areas; however, removal can be highly variable from BMP to BMP and from storm to storm. Results also indicated the bioretention cell depth and soil type may influence the effectiveness of these systems.