Escherichia coli levels and microbial source tracking in stormwater retention ponds and detention basins

Little is known about the spatial and temporal changes that occur with Escherichia coli in urban stormwater systems. The goal of this project was to assess E. coli in urban stormwater detention basins and retention ponds, not connected to the sewer system, to determine temporal and spatial differences and evaluate the sources of E. coli utilizing microbial source tracking (MST). Surface water quality was sampled at three detention basins and five retention ponds during major storm events in the summers of 2018 and 2019. One week after each storm, groundwater and surface water were sampled. The MST samples were taken from storm events and normal flows, for both surface and groundwater. E. coli levels were higher during rain events in both detention basins and retention ponds and infrequently met a recreational standard. E. coli in groundwater was pervasive and infrequently met a recreational standard. The MST analysis found sewage, dog, human, and bird markers during storm events and sewage and bird markers during regular flows. PRACTITIONER POINTS: Rain events had significantly more E. coli than during normal flows in both retention ponds and detention basins. E. coli in groundwater was ubiquitous and fluctuates over time. Microbial source tracking (MST) found bird, dog, human, and sewage markers present during all storm events analyzed.