Relationships among Escherichia coli (E. coli), Total Suspended Solids and Flow for Three Northern Virginia Subwatersheds: Rabbit Branch, Upper Accotink Creek, and Daniels Run




Washington, Marissa

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This project was designed and completed to satisfy the requirements for the M.S. Program in Environmental Science and Policy at George Mason University. Three sites located in Fairfax, Virginia residential areas were chosen to monitor Escherichia coli concentrations between May 18th and July 19th, 2013 and to examine the relationship of E. coli to stream flow, total suspended solids (TSS) and impervious cover. Each site was visited a total of 9 times during the study period. Analysis of data from these sites indicated that they are not meeting the Virginia Department of Environmental Quality (VDEQ) standard of 235 CFU/100 mL for E. coli in recreation streams. The range for E. coli over all three sites was 78 - 19,100 CFU/100 mL. There were also nine samples in which the levels were above the range of the test procedure (>20,000 CFU). This study also suggested that E. coli may respond to increased impervious cover, TSS and rainfall; however, due to a high degree of variability most of the relationships were not significant. Visual examination of the watersheds indicate that there are multiple potential upstream non-point sources including human and animal activity that could contribute to elevated E. coli levels. Because these sites are in violation of state water quality standards, it is imperative that the County and City Storm Water Planning Divisions further investigate and devise plans to fulfill the purpose of the Clean Water Act. Two of the three sites, Daniels Run and Rabbit Branch, could benefit from projects that have been proposed.