Citation:

Pennino, M., J. Compton, AND S. Leibowitz. Trends in Nitrate Drinking Water Violations Across the US. 2017 ESA Annual Meeting, Portland, Oregon, August 06 - 11, 2017.

Impact/Purpose:

Under the Safe and Sustainable Water Resources Research Program, EPA scientists are examining the temporal and spatial patterns of drinking water nitrate violations across the United States. Excess nitrate in drinking water has been a human health concern since the middle of the 20th century. Since 1979, public drinking water suppliers have been required to regularly monitor nitrate levels and EPA is notified when a public water system violates the 10 mg nitrate-N L-1 maximum contaminant level (MCL). The study found an increase in the number and proportion of systems in violation for nitrate over time, nearly doubling from 280 to 527 systems from 1994 to 2010. This analysis identifies specific systems or locations that consistently experience violations of the nitrate MCL or where there are higher populations served by systems in violations, which can then inform management strategies. Currently, it is not fully known what is causing this increase in nitrate violations in drinking water supplies. This analysis, along with future research on the underlying factors driving the violations, may inform decisions on how treatment, source water protection, and other management options could best protect drinking water from nitrate contamination. The results of this study could be important for a number of programs within EPA’s Office of Groundwater and Drinking Water, Regions, and States. This abstract contributes to SSWR4.03C and SSWR3.01B.

Description:

Background/Question/Methods Safe drinking water is essential for the health and well-being of humans and life on Earth. Previous studies have shown that groundwater and other sources of drinking water can be contaminated with nitrate above the 10 mg nitrate-N L-1 maximum contaminant level (MCL), which is known to have adverse health effects, including certain cancers. Public water systems (PWS) across the US have been required since 1979 to report violations of the nitrate MCL to the US Environmental Protection Agency’s Safe Drinking Water Information System (SDWIS). The objective of this research was to use SDWIS data to assess temporal and spatial trends for nitrate violations. We collected data from SDWIS on the number of PWS that violated the nitrate MCL at least once each year. The proportion of systems in violation each year was calculated by diving the number of systems in violation by the total number of active systems that year. The number of people served by systems in violation was calculated by summing the number of people served by each PWS in violation. Results/Conclusions We found that the number and proportion of systems in violation for nitrate significantly increased over time, almost doubling from 280 (0.16%) to 527 (0.33%) systems between 1994 and 2010. The increase in number and proportion of systems in violation is attributed to an increase in violations for groundwater systems, whereas violations for surface water systems have decreased over time. The number of people served by systems in violation varies over time from several hundred thousand to nearly two million, but has decreased from approximately 1,000,000 to 200,000 people between 1997 to 2014. Spikes in the number of people served by systems in violation are attributed to just one or a few surface water systems, but these systems can serve over one million people. Kansas and Nebraska had the greatest proportion of systems in violation, while the greatest number of people served by systems in violation are in Ohio and California. Results show that surface water systems that serve more people generally have been improving over time. In contrast, rural groundwater systems in violation are increasing, as are the average duration of these violations, indicating persistent nitrate problems. In the future we will be investigating associations between land use or anthropogenic inputs and nitrate violations. Understanding where and when violations are most prevalent and what is causing the violations may help inform future management decisions.

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