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PhD Defense

E-IPER Dissertation Defense - Randall Holmes "Strategies for Managing Naturally Occurring Contaminants in Groundwater Basins of the Central Valley, California"

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Event Details:

In Person: Y2E2 299

Virtual: Zoom Webinar


California’s Central Valley provides some of the most productive agricultural land in the world. However, climate change is disrupting the hydrologic cycle and multiple stakeholders are extracting groundwater faster than it can be replenished. Such groundwater overdraft has degraded or depleted drinking water supplies, endangered groundwater dependent ecosystems, and severely damaged both crops and irrigation infrastructure. To address the deleterious pathway we are on, I first qualitatively examine Central Valley farmer perceptions of the California water system through 30 semi-structured interviews. I describe the California farm as a coupled infrastructure system with groundwater as a common pool resource, placing managed aquifer recharge as an economically viable option for sustainable groundwater management. I modify and leverage the Driver-Pressure-State-Impact-Response (DPSIR) framework to provide exploratory descriptions of the economic, social-behavioral, and biophysical context of farmer decision-making with respect to groundwater quality and quantity. I explore farmers’ beliefs about their roles in both creating and mitigating overdraft, and I reveal farmers self-identifying as sustainable stewards of the land not solely motivated by profit. However, I also identify threats from naturally occurring contaminants such as arsenic and uranium. Further, on the basis of current decision support tools for siting managed aquifer recharge on farms, I propose balancing the quantity of planned recharge with mitigation strategies that control the biogeochemical and hydrogeological mechanisms associated with naturally occurring threats. Lastly, my work illustrates the benefit of augmenting managed aquifer recharge siting tools with predictive naturally occurring threat maps created with random forest modeling. I propose a scenario-based case study that emphasizes the need to balance reversing overdraft with maintaining or improving groundwater quality to ensure California has a sustainable water supply for all beneficial uses.

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