Assessing Potential for Managed Aquifer Recharge on the Manastash Alluvial Fan: A Geochemical Analysis
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Date published: July 9, 2025
Authors: Elif A Myers
Reference:
Myers, Elif A., "Assessing Potential for Managed Aquifer Recharge on the Manastash Alluvial Fan: A Geochemical Analysis" (2025). All Master's Theses. 2102. https://digitalcommons.cwu.edu/etd/2102
Abstract:
In south-central Washington, the Yakima River Basin spans 6,100 square miles, encompassing approximately 10% of the state. With a growing population and over 400,000 acres of irrigated cropland, reliable water availability is vital for supporting agricultural irrigation, municipal needs, and aquatic habitats. To ensure water for future use, Managed Aquifer Recharge (MAR), the practice of applying surface water to aquifers for storage or hydrologic system benefit, has been proposed within the Yakima Basin Integrated Plan (YBIP). This research explores the Manastash alluvial fan–located west of Ellensburg, Washington as a potential region for two MAR methods: Shallow Aquifer Recharge (SAR) and Aquifer Storage and Recovery (ASR). Within this study, six subsurface lithologic cross-sections were developed from well logs and geologic maps to characterize hydrogeologic relationships. Water levels within Manastash Creek and two unused wells were monitored using in situ devices to identify surface/groundwater level correlations. Major ion, trace element, and stable isotope geochemistry of 22 groundwater and nine surface water samples were analyzed to further support surface water/groundwater interactions and classify groundwater groupings. Three groundwater hydrochemical groups were identified: Group 1 (high to medium sodium values suggesting older waters), Group 2 (sedimentary wells with light isotopic signatures suggesting little-to-no surface water influence), and Group 3 (relatively heavy isotopic signatures suggesting influence from Yakima River derived waters, likely irrigation). Sedimentary wells with evidence of strong surface water influence (Group 3) were combined with soil infiltration and drainage data, tax parcel information, and estimated seepage velocity calculations to identify four suitable locations for SAR. Additionally, a region of concentrated basalt wells and tax parcel data were combined to identify one potential location for ASR at the fan apex. Suitability analysis results identify specific locations to be further assessed for MAR on the Manastash alluvial fan.
Contact person/agency: Central Washington University Geological Sciences Department
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