Extent and Impacts of Unplanned Wastewater Reuse in US Rivers.

A recently developed watershed-scale hydraulic model (De-facto Reuse Incidence in our Nation's Consumptive Supply [DRINCS]) was applied to estimate municipal wastewater treatment plant (WWTP) contribution to downstream water treatment plant (WTP) influent flow. Using DRINCS and geocoded data for 14,651 WWTPs and 1,320 WTPs, the occurrence of treated municipal wastewater in drinking water supplies is geographically widespread, and its magnitude depends largely on the flow condition and size of the source river. Under average streamflow conditions in this study, the median contribution of wastewater flow to drinking water supplies was approximately 1% and increased to as much as 100% under low-flow conditions (modeled by Q95). Wastewater contributions to nutrient and emerging contaminant loading were estimated and geospatially compared with the findings of the US Environmental Protection Agency's Unregulated Contaminant Monitoring Rule and Long Term 2 Enhanced Surface Water Treatment Rule. In turn, this analysis offers important insights into the treatment challenges facing treatment facilities across the United States. [ABSTRACT FROM AUTHOR]