From field to groundwater: EPA research in the GWMA
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Nitrate contamination of groundwater is an important issue in many agricultural areas within Oregon and across the US. The southern Willamette Valley (SWV) can be used as a case study to understand groundwater nitrate sources, dynamics and management. Because nitrate is a human health concern and high concentrations have been observed in the SWV, the state of Oregon declared the SWV Groundwater Management Area (GWMA) in 2004. A network of monitoring wells for both drinking water and groundwater was established throughout the GWMA and these wells have been sampled by Oregon DEQ since 2006. These monitoring well data were recently analyzed by Cody Piscitelli as part of his MS thesis in OSU’s Environmental Science Graduate Program (Piscitelli 2019). Over the sampling period between 2006-2019, average nitrate concentrations exceeded the state of Oregon’s 7 mg nitrate-N L-1 Action Level in 33% of the SWV-GWMA monitoring wells, and average concentrations exceeded the U.S. Environmental Protection Agency’s (EPA) Maximum Contaminant Level (MCL) of 10 mg nitrate-N L-1 for 12% of the wells (Figure 1). Approximately 57% of all monitoring wells showed an increase in nitrate during the entire sampling period. The mean nitrate concentration across all monitoring wells increased significantly from 5.41 mg nitrate-N L-1 during the 2006-2011 sampling period to 6.28 mg nitrate-N L-1 during the 2012-2019 sampling period, with variability among wells in a particular year (Figure 2). The findings indicate that despite the greater public awareness of the issue of groundwater nitrate contamination in the SWV-GWMA, concentrations have continued to increase over the last 14 years (Piscitelli 2019).