Working with the Community for Nitrate Monitoring Southern Willamette Valley Groundwater Management Area.

The southern Willamette Valley (SWV) is home to diverse agricultural systems, interspersed with small towns, cities and natural areas. Throughout the SWV, groundwater is often the source of drinking and irrigation water. About 90% of the land area in the SWV GWMA is agriculture, and 90% of N inputs to the land area were estimated to be from farm fertilizers. In 2000-2001, 20% of 476 shallow wells (< 75 feet deep) tested had nitrate-N values over 7 mg/L. Oregon Department of Environmental Quality (ODEQ) established the SWV Groundwater Management Area (GWMA) in 2004 after the high wells were retested in 2002 and 90% were still above the 7 mg/L action level. GWMA is a program to engage landowners and community members in characterizing the sources of the nitrate groundwater contamination and implementing measures to address the non-point sources of pollution.  The SWV GWMA committee consists of county commissioners, realtors, area commercial farmers, and representatives from the fertilizer industry, public water supply and local watershed councils. To monitor the long term trends in groundwater, ODEQ quarterly samples 17 domestic and 26 groundwater monitoring wells. Nitrate concentrations in the Willamette River are usually below 1 mg/L of NO₃-N, tending to have lower nitrate concentrations than many groundwater samples. Over the time period from 2012 and 2014, 12 out of all 37 wells (33%) showed a decline in nitrate concentrations, but 54% of the highest nitrate value wells (6 out of 11) showed a decline in nitrate concentrations over time.  Ongoing work compares recent trends in crops, nutrient management practices and fertilizer sales with the trends in field leaching losses and in well water, in order to determine how groundwater quality is responding to changing agricultural practices with an eye toward understanding the social, economic and environmental drivers of these trends.