Removal of bacterial indicators of fecal contamination in urban stormwater using a natural riparian buffer
International Conference on Urban Drainage , 2005
Casteel, M.J., Bartow, G., Taylor, S.R., Sweetland, P.
Little information is available on the ability of naturally-occurring riparian buffers to remove waterborne microbes from urban stormwater runoff. In the present study, bacterial indicators of fecal contamination were quantified in stormwater before and after intentional diversion to a natural riparian buffer (RB) adjacent to a lake located in the City of San Francisco, California. Analysis of lake water showed that levels of Escherichia coli and total coliforms increased significantly during storm events, indicating the presence of nonpoint sources of fecal contamination in the area surrounding the lake. When 0.44 million L (5,700 L/min) of stormwater was intentionally diverted and discharged to the RB, lake levels of E. coli, enterococci, and total coliforms were about 2-3 log10 (99-99.9%) lower than levels in stormwater. The RB was less effective in reducing bacterial levels during some major storms (>4 cm precipitation in <48 h) with higher inputs (several million L), but large amounts of uncontrolled surface runoff had been observed entering the RB and Lake Merced during those events. These results suggest that the RB evaluated in this study worked effectively to reduce the numbers of bacteria in stormwater from entering a body of water in an urban setting.