USGS Washington Water Science Center
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9722-AUF - Developing and Utilizing Isotopic and Tracer Tools to Evaluate the Source and Movement of Nitrate in Contaminated Ground Water in the Lower Umatilla Basin, Oregon - Completed FY2006
Problem - There are a variety of nitrate sources present in the Umatilla basin including septic tanks, CAFOs, explosives, fertilizer, and food processing waste (Grondin and others, 1995). Therefore, development of isotopic tools to distinguish which of the five sources of nitrate have contributed to contaminating particular areas is needed in order to assist agencies in effectively focusing their resources on reducing nitrate loading to the ground-water system. With additional information about how long the water has been traveling, it can be determined whether the nitrate is from legacy or current management practices.
Objectives - The objective of this study is to develop isotopic and tracer tools to identify sources of nitrate in ground water in the Lower Umatilla Basin Ground Water Management Area (GWMA). This study will attempt to assess 1) the nitrogen and oxygen stable isotopic signature in ground water from each type of nitrate source if not adequately defined in the literature and 2) the age of the water carrying the nitrate to determine whether the nitrate is from current or historical land management practices. This work will examine the ability of isotopic tools to fingerprint selected nitrate sources in the GWMA and expose the limitations of the method.
Relevance and Benefits - The USGS Strategic Plan (https://www.usgs.gov/stratplan/stratplan_rev/) has a Mission Goal of improving the understanding of our Environment and Natural Resources. In particular, the USGS works to provide customers with an integrated understanding of natural systems at various scales, with more and better predictive tools and decision support systems. The USGS Washington Water Science Center Science Plan (http://wwwdwatcm.wr.usgs.gov/uo/internal/sac/scienceplan.2000.wa.pdf) identifies a need to better predict land-use effects on surface-and ground-water quality. This project will develop a tool to allow EPA and Oregon Department of Environmental Quality to better determine the sources of nitrate in the ground-water of the Lower Umatilla Basin. With this information, these agencies can focus on the appropriate management practices to reduce nitrate levels in the basin. This work is expected to have transfer applications to other basins.
Approach - The following site selection and sampling work plan is anticipated: