Geosyntec recently presented on "Microbial Source Tracking" at the Georgia Association of Water Professionals (GAWP) Annual Conference. The topic generated interesting discussions on how municipalities target illicit discharges to comply with their Municipal Separate Storm Sewer System (MS4) permit.
The presentation focused on the use of Microbial Source Tracking (MST) to target illicit discharges to comply with Municipal Separate Storm Sewer System (MS4) permits; including an ongoing study for the Atlanta Regional Commission (ARC) where MST is being utilized to analyze the relationship between septic system density and fecal coliform impaired downstream waters.
Georgia's MS4 permits, issued by the GA EPD, require a rigorous Illicit Discharge Detection and Elimination (IDDE) program to be implemented over the five-year permit term, including sanitary sewer infiltration controls to eliminate seepage and spillage from municipal sanitary sewers and septic systems as appropriate within the jurisdiction. Conventional parameters and dye testing are typically used to prioritize outfalls and locate illicit connections and leaks from sanitary sewers. However, concentrations of bacteria and nutrients (TMDL pollutants) at many MS4 outfalls sometimes remain elevated and it is unknown if human sewage sources remain or if non-sewage sources are contributing to the bacteria concentrations.
Using MST tools, including human DNA markers, present in sewage, MS4s can identify where further network investigations are needed to locate additional sources of bacteria and nutrients. Through a study design that includes wet and dry weather sampling across outfalls, sampling at selected outfalls, and sampling of sources including surface runoff, catch basin sediments, and known illicit discharges, MS4s can identify sources contributing the greatest load to outfalls. Using this information, MS4s are able to modify their IDDE program to more effectively and efficiently eliminate sewage sources, evaluate use of green infrastructure and other best management practices to achieve required TMDL pollutant load reductions, and by more directly targeting higher risk human waste sources, improve recreational water quality and public health protection.
Learn more about MST by watching this short video: youtu.be/psXkqTc9eeE
Learn more about Brandon Steets here: https://www.geosyntec.com/people/brandon-steets
Learn more about Ganesh Krishnan here: https://www.geosyntec.com/people/ganesh-krishnan
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