The priorities for this project were to use local data wherever possible and create a static range of nitrogen availability at low, medium, and high points at the time of completion. In addition, the groundwater advisory committee needed a living resource that could be updated when new information became available, and could be used at a variety of geographic scales to evaluate next steps for addressing current and preventing future nitrate contamination. This pie chart shows the relative size of the possible nitrogen sources, estimated at the medium level.
Nitrogen Loading Assessment in Lower Yakima Valley
A groundwater management area was established in the Lower Yakima Valley in 2012 in response to an ongoing history of high nitrate concentrations in well samples. As part of the work to evaluate the potential contributions to groundwater nitrate the Groundwater Advisory Committee directing this work commissioned WSDA and Yakima County to evaluate the amount of nitrogen available from all major sources. The sources evaluated by WSDA were concentrated animal feeding operations (consisting of animals pens and manure lagoons), irrigated agriculture, and atmospheric deposition. The sources evaluated by Yakima County were residential, commercial, industrial, and municipal sources, consisting of septic systems, small-scale farms, and residential lawn fertilizer.
The outcome of this project was a written report documenting the methodology, assumptions, and inputs for each category as well as the resources (spreadsheets and a geodatabase) that could be used to update calculations as available information changes over time. The map shown here represents a potential use of the geodatabase to examine the different possible nitrogen sources in a specific area. This map shows sources estimated at the high level. An interactive webmap is hosted at the Yakima County Website.
Download our full report on this study: Estimated Nitrogen Available for Transport in the Lower Yakima Valley Groundwater Management Area