E. Coli in the Tanyard Creek Combined Sewage Overflow: a Spatial and Temporal Review Coordinated with Weather Patterns

Abstract E. COLI IN THE TANYARD CREEK COMBINED SEWAGE OVERFLOW: A SPATIAL AND TEMPORAL REVIEW COORDINATED WITH WEATHER PATTERNS By Hannah-Leigh Crawford August 2019 INTRODUCTION: Tanyard Creek is an urban creek in metro Atlanta contained in a large urban sub-watershed that sends stormwater to drain into the Chattahoochee River. The creek is considered impaired, with signage warning the public not to play, swim, or fish in creek. As an urban creek, it is subject to sewage overflow from one of the city of Atlanta’s combined sewer overflow (CSO) facilities, the Tanyard Creek CSO, as well as runoff from the surrounding commercial and residential areas, which may carry microbial contaminants into the creek. The creek is partly surrounded by an urban greenspace containing walking and biking paths and playgrounds, making it a candidate for remediation and future use for recreation. To understand the patterns of possible microbial contamination in this type of urban creek, the fecal indicator Escherichia coli was evaluated in the creek over time. AIM: This research will determine the trends of E. coli in Tanyard Creek and if E. coli counts differ temporally (over the course of a year) and spatially (from sampling site to sampling site). Additionally, rainfall data from the National Weather Service will be used to determine if there is a relationship between rainfall amounts and E. coli counts at 24, 48, and 72 hours prior to sampling, as well as cumulatively. METHODS: Water samples were collected weekly for roughly 47 weeks at 10 sites downstream from the Tanyard Creek CSO. The 10 sites were spaced along a half mile stretch of creek that included a concrete channel, a beaver dam, and a railroad bridge. All samples collected from the creek were then brought to the lab for analysis of microorganisms through membrane filtration for E. coli using BioRad RAPID\u27E. coli 2™ bacterial assay. RESULTS: E. coli is present in Tanyard Creek at levels higher than the U.S. Environmental Protection Agency standards. This data indicates temporal trends; during the summer months (June-September) there are higher counts of E. coli. Also, E. coli from all sampling sites differed significantly by date. This data does not indicate spatial trends, as the E. coli from all dates by sampling site did not differ significantly. For all rainfall levels—24, 48, and 72 hours prior to sampling, as well as cumulatively, there was not a statistically significant relationship between rainfall and E. coli levels. These high levels of fecal indicator bacteria demonstrate that the creek is vulnerable to bacterial and viral contamination that may pose risks of waterborne disease. These risks might be mitigated if the creek is to be reclaimed in the future as a recreational urban greenspace, potentially requiring changes in urban stormwater and runoff management