USGS Washington Water Science Center
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More than 80 percent of drinking water in the mid-Columbia Basin comes from ground water. In Adams, Franklin, and Grant Counties, nitrate concentrations in water from about 20 percent of all drinking-water wells exceed the U.S. Environmental Protection Agency maximum contaminant level for nitrate. The three counties jointly formed the Columbia Basin Ground Water Management Area (GWMA) in February 1998, and the first goal was to reduce nitrate concentrations in ground water.
To help the counties reduce concentrations of nitrate and monitor the quality of the ground-water system, the USGS is determining the horizontal and vertical distribution of nitrate concentrations in ground water in the three counties by collecting new data to fill gaps in the data set and analyzing the trends in nitrate concentrations over time. The data set is also being analyzed for correlations between concentrations of nitrate and environmental and anthropogenic factors such as well depth, proximity to irrigation canals, and land use. The USGS is also developing a long-term monitoring plan to help the counties identify temporal trends in regional nitrate concentrations in ground water and how they might affect the availability of low-nitrate drinking water.