Urban Wet-Weather Flows: Sources of Fecal Contamination Impacting on Recreational Waters and Threatening Drinking-Water Sources

Abstract

Discharges of urban stormwater and combined sewer overflows (CSOs) contribute to fecal contamination of urban waters and need to be considered in planning the protection of recreational waters and sources of drinking water. Stormwater characterization indicates that Escherichia coli counts in stormwater typically range from 103 to 104 units per 100 ml. Higher counts (10(5) units/100 ml) suggest the presence of cross-connections with sanitary sewers, and such connections should be identified and corrected. Fecal contamination of stormwater may be attenuated prior to discharge into surface waters by stormwater management measures, which typically remove suspended solids and attached bacteria. Exceptionally, stormwater discharges in the vicinity of swimming beaches are disinfected. The levels of indicator bacteria in CSOs can be as high as 10(6) E. coli per 100 ml. Consequently, the abatement of fecal contamination of CSOs is now considered in the design of CSO control and treatment, as for example stipulated in the Ontario Procedure F-5-5. CSO abatement options comprise combin ations of storage and treatment, in which the CSO treatment generally includes disinfection by ultraviolet (UV) irradiation. Finally, indicator bacteria data from Sarnia (Ontario) were used to demonstrate some fecal contamination impacts of wet-weather flows. In wet weather, the microbiological quality of riverine water worsened as a result of CSO and stormwater discharges, and the recreational water guidelines for indicator organisms were exceeded most of the time. Local improvements in water quality were feasible by source controls and diversion of polluted water.

Land cover controls on summer discharge and runoff solution chemistry of semi-arid urban catchments

“…Since there are no combined sewers in the Tucson Basin, overflow of untreated sewage is not a potential source of E. coli (e.g. Arnone and Walling, 2007;Marsalek and Rochfort, 2004).…”

Sediment can be a reservoir for coliform bacteria released into streams

“…The surface water outbreaks tended to occur within a month of the storm, and monitoring confirmed that coliform bacteria levels rise dramatically during or immediately following storm events (Hyland et al, 2003;Marsalek and Rochfort, 2004). Coliform bacteria are typically not harmful to humans, but they are monitored as indicator organisms to detect the possible presence of fecal contamination and human health risks.…”

Monitoring Recreational Waters: How to Integrate Environmental Determinants

“…CSOs may represent a health risk for people in contact with these waters since the principal source of bacteria it contains is from human waste, which can contain large quantities of fecal pathogens [22]. E. coli concentration associated with CSOs can reach more than 10 6 /100ml, which it is much higher than recreational water guidelines [23]. Wastewater treated by wastewater treatment plants can also contain large amounts of fecal bacteria if these waters are not disinfected before being discharged into watercourses, placing people swimming in waters in close proximity to these discharges at higher risk for health problems [24].…”