2012 journal article
Indicator Bacteria Performance of Storm Water Control Measures in Wilmington, North Carolina
JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING, 138(2), 185–197.
Indicator bacteria are a common source of impairment in surface waters in the United States. Urban storm water runoff has been identified as a contributor to elevated indicator bacteria concentrations. Six storm water control measures (SCMs) were monitored in Wilmington, North Carolina, for E. coli and enterococci. Monitored SCMs included two storm water wet ponds, two bioretention cells, and two storm water wetlands. Sandier watersheds in Wilmington potentially lead to differences in SCM performance for indicator bacteria compared to SCMs implemented in clayey watersheds. Results showed E. coli and enterococci concentration reductions between 70 and 98% for the two wet ponds and a bioretention cell with a 60-cm-deep fill media. Other SCMs showed poor removal of indicator bacteria, in some cases negative, with storm water wetlands performing the poorest overall for the three SCM types. Further analysis showed that SCMs with high concentration reductions tended to have geometric mean effluent concentrations lower than the U.S. EPA’s target surface-water concentration for E. coli. Conversely, no SCM had a geometric mean effluent enterococci concentration lower than the U.S. EPA target value. SCM geometric mean effluent concentrations were typically higher during North Carolina’s swimming season between the beginning of April and the end of October, although no statistically significant relationship could be found (p<0.05). Despite a lack of statistically significant relationships, the potential for higher effluent indicator bacteria concentrations from SCMs during the peak recreational season may have implications for both public health and watershed management and should be further evaluated by the scientific community.