Extent and Impacts of Unplanned Wastewater Reuse in US Rivers

Abstract

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.

Modeled De Facto Reuse and Contaminants of Emerging Concern in Drinking Water Source Waters

“…For DWTPs with higher levels of DFR under average flow (>1–5%), the frequency of CEC detection and CEC concentrations should be high enough to detect by modern analytical methods. Lower DFR values may have CECs that occur below current analytical detection limits (Rice et al ). Thus, DRINCS emerges as a potentially useful tool to identify DWTPs at higher risk for CEC occurrence, where subsequent monitoring could be focused.…”

“…The DRINCS model, previously developed and validated by Rice et al (, ) and Rice and Westerhoff (), is a GIS model that incorporates spatially resolved data layers on the national hydrologic network. The outputs of DRINCS are calculated values of DFR linked with geospatial locations that can be mapped.…”

“…Raw drinking water supplies are commonly under the influence of treated wastewater discharged upstream of drinking water treatment plant (DWTP) surface water intakes, a situation identified as unplanned or unintentional indirect potable reuse (i.e., de facto reuse [DFR]). For drinking water supplies serving more than 10,000 people from surface water sources, roughly half of these facilities in the United States are affected by at least one upstream treated wastewater discharge, based on previous geographical information systems (GIS)‐based modeling efforts (Rice et al , ; Rice & Westerhoff ). Concurrently, studies of drinking water sources have detected pharmaceuticals and other contaminants of emerging concern (CECs) of wastewater origin when these sources are located downstream of treated wastewater discharge locations (Bradley et al , Glassmeyer et al ).…”

“…To better understand a drinking water utility's potential contribution to human or ecological exposure to organic CECs of wastewater origin under a range of streamflow conditions, a model (De Facto Reuse in our Nation's Consumable Supply [DRINCS]) has been developed to estimate the DFR across the United States (Rice et al , ; Rice & Westerhoff ). Herein we compare results from a specific sampling effort analyzing surface water intakes from 22 surface water treatment plants for 192 organic CECs, with predictions of DFR from DRINCS.…”

Drinking water vulnerability in less-populated communities in Texas to wastewater-derived contaminants

“…6 Additionally, some CECs lead to N-nitrosodimethylamine (NDMA) disinfection by-product formation in drinking waters after chlorination. [7][8][9] Furthermore, the public perception of CECs is unfavorable, despite evidence of their minimal human health risk because of the low exposure potentials in drinking water. [10][11][12][13] De facto reuse (DFR) occurs when a municipality withdraws water from a river or reservoir that includes treated wastewater discharged from upstream WWTPs.…”