Shergill, S., Pitt, R. 2004. Quantification of Escherichia Coli and Enterococci Levels in Wet Weather and Dry Weather Flows. WEFTEC, New Orleans, Louisiana. Pages 746-774

bacteria, IDDE, septic systems, stormflow

The main objective of this research was to identify possible sources of E. coli and enterococci bacteria in dry and wet-weather flows in storm drainage systems. A further objective of this study was to find how E. coli and enterococci could be effectively used to identifying the presence of inappropriate sanitary sewage in storm drainage systems during dry weather. Four representative source area types were sampled during this research; including rooftops, parking lots, open spaces, and streets. Two parallel sites were sampled for each source area type; one affected by birds and other animals, and another set with less influence from birds and other animals. A section of Cribbs Mill Creek in Tuscaloosa, Alabama, was also selected for dry weather sampling at outfalls. Overall, total coliforms, E. coli and enterococci bacterial analyses were conducted on 202 wet weather and 278 dry weather flow water samples. During this study, sewage samples were compared with wet weather and dry weather source area samples (from the project reference sample library). The probability of the sewage and source area sample bacteria levels being significantly different was determined using the Mann Whitney test. It was found that the dry-weather outfall samples showing E. coli and enterococci levels higher than 12,000 MPN/100 mL and 5,000 MPN/100 mL respectively, are likely contaminated by sanitary sewage. Levels lower than this can be caused by other sources, such as irrigation runoff, carwash water, or laundry water.