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In order to delineate areas where high nitrates in groundwater occur, Ecology used monitoring data, USGS nitrate risk studies, and landscape patterns of contributing factors to nitrate contamination. Ecology then drafted initial boundaries to consider for Nitrate Priority Areas based on the evidence and topography. Areas were then inventoried for metrics to be used for prioritization. See Washington Nitrate Prioritization report at https://fortress.wa.gov/ecy/publications/documents/1610011.pdf for more information. |
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In order to delineate areas where high nitrates in groundwater occur, Ecology used monitoring data, USGS nitrate risk studies, and landscape patterns of contributing factors to nitrate contamination. Ecology then drafted initial boundaries to consider for Nitrate Priority Areas based on the evidence and topography. Areas were then inventoried for metrics to be used for prioritization. See Washington Nitrate Prioritization report at https://fortress.wa.gov/ecy/publications/documents/1610011.pdf for more information. |
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Laurie Morgan, LHG, Dept. of Ecology Water Quality Program |
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<DIV STYLE="text-align:Left;"><DIV><DIV><P><SPAN><SPAN>The Washington State Department of Ecology (Ecology) Water Quality Program undertook the Nitrate Prioritization Project in 2014 (Morgan, 2014) because of growing concerns about groundwater contamination by nitrates, and the inability to display and evaluate nitrate data on a statewide basis. </SPAN></SPAN></P><P><SPAN><SPAN>This report originated from the agriculture and water quality talks that took place in 2012. Participating agencies agreed that if data exists, everyone should be able to see it in one central location. Agencies that contributed included the Washington Dept. of Ecology, Washington Dept. of Health, Washington Dept. of Agriculture, U.S. Environmental Protection Agency, U.S. Natural Resource Conservation Service, U.S. Geological Survey, and the Washington Conservation Commission. </SPAN></SPAN></P><P><SPAN><SPAN>The Safe Drinking Water Act nitrate limit for delivery of water from public water systems is 10 mg/L. This limit has been exceeded in public water supplies and private wells in various areas of the state going back decades. Not only is contaminated groundwater a public health issue, treatment is also very costly to the public water supply systems and individual households who must deal with contamination on their own. </SPAN></SPAN></P><P><SPAN><SPAN>The goals of this project were to: </SPAN></SPAN></P><UL><LI><P><SPAN><SPAN>Collect and organize statewide information about nitrate monitoring results, the physical factors that tend toward nitrate contamination, and United States Geological Survey (USGS) risk studies that evaluate the physical factors against monitoring results. </SPAN></SPAN></P></LI><LI><P><SPAN><SPAN>Delineate areas where high nitrates in groundwater occur. </SPAN></SPAN></P></LI><LI><P><SPAN><SPAN>Prioritize those areas by potential impacts to people and resources. </SPAN></SPAN></P></LI><LI><P><SPAN><SPAN>Make the information available to everyone. </SPAN></SPAN></P></LI></UL><P><SPAN><SPAN>The inputs for developing candidate Nitrate Priority Areas include: </SPAN></SPAN></P><UL><LI><P><SPAN><SPAN>A single database of nitrate sampling results for groundwater compiled from state and federal databases. </SPAN></SPAN></P></LI><LI><P><SPAN><SPAN>USGS nitrate risk studies. </SPAN></SPAN></P></LI><LI><P><SPAN><SPAN>Surficial geology, soil properties, topography, well locations and depths, agricultural land use, irrigated areas, annual average precipitation, nitrate concentrations, and population. </SPAN></SPAN></P></LI></UL><P><SPAN><SPAN>Monitoring data from the USGS and the Washington State Departments of Health and Ecology were collected and summarized. The well locations were mapped using a Geographic Information System (GIS). </SPAN></SPAN></P><P><SPAN><SPAN>Clusters of wells where a sample has exceeded 10 mg/L are a strong indicator that groundwater at that location is at high risk of, or currently is contaminated by nitrate. Other indicators include USGS nitrate risk analyses, Natural Resources Conservation Service (NRCS) soil drainage classes and travel time through the soil profile (Ksat), surficial geology, recharge and well depths.</SPAN></SPAN></P><P><SPAN><SPAN>Boundaries for candidate Nitrate Priority Areas were developed based on section lines that approximate natural boundaries. These areas will be subject to review and change where appropriate. Once the proposed Nitrate Priority Areas have been reviewed, section line-based boundaries may be replaced by natural boundaries where appropriate. </SPAN></SPAN></P><P><SPAN><SPAN>Time series plots were produced for wells with four or more sample results with at least one result over 5 mg/L. This resulted in a distribution of over 1200 graphs across the state. These are accessible through the GIS as a popup from the well location point for those who have a GIS system with this capability, and who request and receive the necessary files. A web-based application would make these graphs widely and easily available. </SPAN></SPAN></P><P><SPAN><SPAN>Challenges with databases always include checking for errors, such as the occasional locational or data entry error. Care must be used to understand the limitations of the data and the peculiarities of each data source. These issues are described more in this report. </SPAN></SPAN></P><P><SPAN><SPAN>Recommendations include developing a web application to make this information easily accessible by anyone with internet access, and automating the data downloads so they are easily updated. Management of nitrate sources to prevent groundwater contamination should be adjusted for sensitive conditions like excessively draining soils and very hydrologically conductive geologic materials. Nitrate source loading needs to be reduced in impacted areas to prevent groundwater contamination. </SPAN></SPAN></P><P><SPAN><SPAN>Results of this study can be used to protect public drinking water supplies by focusing actions on areas within the state that have the highest potential for impacts due to nitrate contamination of groundwater.</SPAN></SPAN></P><P><SPAN /></P></DIV></DIV></DIV> |
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Washington Groundwater Nitrate Priority Areas |
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["Washington State Department of Ecology","ECY","Water Quality Program","WQ","GEO","geoscientificInformation","Health","water","United States Geological Survey","USGS","risk studies","landscape","groundwater","nitrate","NO3"] |
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