Exploring the Suitability of a Modeling Approach to Estimate Contaminant Occurrence in Drinking Water Sources

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Scientists explored the suitability of the DeFacto Reuse in our Nation's Consumable Supply (DRINCS) model to estimate the likelihood of contaminants from upstream wastewater discharges to enter drinking water facility intakes.

Diagram showing how wastewater discharging from wastewater treatment plants

Diagram showing how wastewater discharging from wastewater treatment plants might flow downstream and end up as part of the source water for drinking-water treatment plants.

(Credit: Justin Conley, US Enviromental Protection Agency. Public domain.)

Lakes and streams in the United States are simultaneously used as sources of drinking water and as the destination for permitted treated wastewater discharges. Water intakes at drinking-water facilities that use surface waters are often downstream from urban areas where treated wastewater is discharged, resulting in unintentional, or "de facto," reuse of wastewater for drinking water.

To protect the safety of drinking water, efficient tools are needed to understand the likelihood of contamination from upstream domestic wastewater discharges and the hydrologic conditions under which contamination may be the greatest.

To that end, scientists from the U.S. Geological Survey (USGS) Water and Wastewater Infrastructure team, U.S. Environmental Protection Agency (EPA), and University of Arizona explored the suitability of a modeling approach to provide drinking-water facilities with a tool to understand the likelihood of contaminants from upstream wastewater origin to enter drinking water intakes under a range of streamflow conditions.

Scientists compared results from a specific sampling effort analyzing surface water intake samples from 22 drinking-water facilities for 192 organic contaminants, with predictions of the percentage of upstream wastewater reused from the DRINCS model.

Results from this study document that the DRINCS model reuse values were correlated with the sum of contaminant concentrations measured in this study. The findings indicate that the DRINCS model can be a useful tool to provide estimates of the likelihood of a water supply containing contaminants of wastewater origin from upstream sources.

Certain contaminant groups such as perfluorinated chemicals showed less correlation with reuse values, which could be due to significant non-wastewater-treatment-plant contributions of these contaminants upstream from sampled facilities.

Although the comparison of modeled reuse values and measured concentrations in this study indicates the general suitability of the DRINCS model, the results also indicate that predictive capabilities could be enhanced by collection of continuous stream flow information in closer proximity to drinking water facilities.

This study is part of the long-term strategic goal of the USGS Environmental Health Program to provide comprehensive science on sources, movement, and transformation of contaminants and pathogens in drinking-water supplies and in built water and wastewater infrastructure.

The work was partially supported by the Arizona State University Decision Center for a Desert City (NSF Award No. 0951366), Central Arizona-Phoenix Long-Term Ecological Research (DEB-1637590), and Vietnam Education Foundation. The chemical analysis data were funded in part by EPA through Interagency Agreement DW14922330 to USGS and through programmatic support of the USGS Environmental Health Program (Toxic Substances Hydrology and Contaminant Biology), the EPA's Office of Research and Development, and the Office of Chemical Safety and Pollution Prevention.