Citation:

Pennino, M., S. Leibowitz, J. Compton, R. Sabo, Ryan A Hill, S. LeDuc, AND M. Beyene. Explaining Trends in Drinking Water Nitrate. Water for Food Global Forum at the University of Nebraska, Lincoln, Nebraska, October 17 - 23, 2021.

Impact/Purpose:

Under the Safe and Sustainable Water Resources National Program, EPA scientists have examined 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 maximum contaminant level (MCL).  The results of this presentation, except for project # 3 (which describes preliminary results), have previously been published (projects 1, 2, & 4).  These studies have elucidated the spatial and temporal patterns of drinking water nitrate MCL violations across the conterminous United States.  These studies found an increase in the proportion of systems in violation for nitrate between 1994 and 2009, but a decline in both groundwater and surface water sourced nitrate violations from 2009 to 2016.  The spatial patterns of nitrate violations are driven by climate, land use, and N input variables, and the regions of highest risk for nitrate violations are often in the southwest.  Wildfires are associated with increase nitrate violations and changes in N inputs and drinking water system treatment are both important at reducing nitrate violations. These studies may inform decisions on how treatment, source water protection, and other management options could best protect drinking water from nitrate contamination. 

Description:

This presentation highlights the results of several research projects related to explaining the temporal and spatial trends in drinking water nitrate violations across the conterminous United States.  Excess nitrate (NO3-) in drinking water is a human health concern, especially for young children.  The results from the first study assessed temporal and geographic trends for violations of the 10 mg NO3--N/L maximum contaminant level (MCL) in the conterminous U.S.  The second study shows results of models used to determine the drivers of nitrate violations across the conterminous U.S. and to predict where public water systems are at risk of exceeding the NO3- MCL.  The third study attempts to determine the main causes for temporal declines in drinking water nitrate violations, such as due to reductions in N inputs, improved drinking water system treatment, or better source water protection measures.  The fourth study examines post-wildfire effects on nitrate violations and concentrations, and a planned fifth study will examine whether future changes in temperature, precipitation, land use, and N inputs may alter where drinking water systems are most at risk for violations of the NO3- MCL.  The results of these studies show that most NO3- MCL violations are in small, non-community, groundwater systems, and some groundwater systems have persistent nitrate contamination, but one large surface water system in violation can potentially impact millions of people.  The results also show the locations and factors (e.g., nitrogen inputs, precipitation) that are associated with higher risks for drinking water nitrate violations.  Changes in both nitrogen inputs and PWS operation both play a role in shaping the trends in DW nitrate.  On average, wildfires are associated with increased surface water NO3- violations and the elevated NO3- can last multiple years post wildfire.  This work could help inform management decisions aimed at minimizing public health risks associated with drinking water nitrate.

Record Details: