Document Type

Thesis

Date of Degree Completion

Spring 2020

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Carey Gazis

Second Committee Member

Lisa Ely

Third Committee Member

Susan Kaspari

Abstract

Currently in the Yakima River Basin more people possess surface water rights than there is available surface water. As a result, the local community devised the Yakima River Basin Integrated Water Management Plan, with the goal of creating a sustainable source of water for the foreseeable future. One of seven elements outlined in this plan is groundwater storage. The idea is to take available water during high spring flows and store it in the subsurface. The water will then be used to increase stream flows and decrease stream water temperatures during the summer months. A main challenge associated with groundwater storage is determining the fate of the recharged water. In this project we analyzed major ions and stable isotopes of surface waters and groundwaters within three regions (Roslyn, Kittitas Valley and Moxee Valley) to determine water–rock interactions, relative residence times, recharge regimes and groundwater surface-water interactions. We found that irrigation water generally had heavier isotopic values (δD > –115‰) and higher nitrogen levels when compared to natural groundwater. This allowed us to identify which aquifers were dominantly recharged by irrigation water versus aquifers that are recharged naturally (typically by snowmelt). Using our geochemical data, combined with known hydrogeologic units and structures we created conceptual models of groundwater relationships at each site. Additionally, we identified potential shallow aquifer recharge sites that have deep surficial aquifers overlain by large vadose zones. These conceptual models and identified locations can be used to inform future management decisions regarding groundwater storage.

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