Description: Pursuant to guidance provided in the Department of Environmental Quality (DEQ) policy memorandum entitled "Policy for Addressing Degraded Ground Water Quality Areas" dated March 1, 2000, a statewide list of significantly degraded areas with nitrate was developed. In 2002, the DEQ, in cooperation with the Idaho Ground Water Monitoring Technical Committee (GWMTC) published a ranking of 25 Nitrate Priority Areas (NPAs). The NPAs are areas where elevated levels of nitrate have been found in ground water. In 2013-14, incorporating recent monitoring, 34 NPA's were evaluated and prioritized. DEQ, in conjunction with the GWMTC revised the NPAs published in 2008. The revisions utilized data collected since the original NPAs were developed to evaluate ground water quality changes in existing NPAs and to identify new areas with nitrate degraded ground water. In the summer of 2011 the GWMTC began the process of revising the NPAs. The minimum criterion for a Priority 1 NPA is 25% of sampled wells have nitrate levels at or above 5 milligrams per liter (mg/L). The state and federal drinking water standard, as well as the Idaho Ground Water Quality Standard for nitrate is 10 mg/L. Within a Priority 2 NPA 50% of the sampled wells have nitrate levels at or above 2 mg/L. Almost all developed areas of the state meet this criterion. The NPA Ranking Process (Ranking Process), developed by DEQ, in consultation with the GWMTC, provides the rationale for numerically ranking areas in Idaho with identified ground water degradation from nitrates. The statewide priority list created through this process will be used to prioritize the implementation of protective management strategies or corrective action measures within the NPAs. In the summer of 2011, DEQ began collecting and compiling nitrate results and well location data from the numerous agencies monitoring ground water quality in Idaho. Well location information, sampling date, and nitrate concentration data were received and compiled by DEQ. Spatial information was reconciled and integrated into a Geographic Information System (GIS) coverage. Sources of data included the DEQ public water system database, the Statewide Ambient Ground Water Quality Monitoring Network (Statewide Program), numerous U.S. Geological Survey (USGS) studies, DEQ regional and local monitoring projects, regional studies conducted by the Idaho State Department of Agriculture (ISDA), and dairy sampling by ISDA. Data from 1990 into 2011 were plotted with the corresponding nitrate value. The 2008 NPAs were based on data from 1990 - 2007 and the 2012 NPAs were based on data from 1990-2011. The use of more recent data resulted in a difference of sample numbers between the 2008 and 2012 NPA analysis. For sites with multiple values the most recent value was used. Data from site-specific monitoring projects associated with known point sources of nitrate contamination were not included in the data set. Ground water quality data from about 11,000 wells statewide were compiled and evaluated to develop the 2012 NPAs. The NPAs contain over 4,000 of the 11,000 wells and encompass a combined area of 2,138,930 acres. Approximately 400,000 people are estimated to live within the boundaries of the NPAs. http://www.deq.idaho.gov/media/1117845/nitrate-priority-area-delineation-ranking-2014.pdf
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