Managed Aquifer Recharge in Central Arizona: Long-Term Storage Credits, Central Arizona Groundwater Replenishment District and Effluent Reuse

Abstract

The state of Arizona utilizes a valuable water management tool, Managed AquiferRecharge (MAR), in response to water scarcity and population growth. MAR consists of storing water in an aquifer through a process called artificial recharge. This research analyzes three different aspects of MAR in Central Arizona: a tool called long-term storage credits (LTSCs), a mechanism called the Central Arizona Groundwater Replenishment District (CAGRD), and means for recharge: the reuse of effluent. This research follows a three-article dissertation format. The main body of this dissertation is contained in Appendixes A, B, and C. Appendix A offers a descriptive analysis of sales and purchases of LTSCs and connects LTSCs to Arizona's laws and regulations that ensure sustainable use of water in the most populated areas of the state. LTSCs represent a quantity of water stored in the aquifer. Using data collected and maintained by the Arizona Department of Water Resources (ADWR), this study examines sales of LTSCs to reveal patterns of marketbased transactions. Analysis of 23 years of public records shows several trends: (1) LTSC transactions have been increasing since 2003; (2) municipal water providers and investment firms have been active participants in LTSC transactions; (3) the greatest transaction volumes involve governmental entities established by state law with groundwater recharge and replenishment obligations. The experience with LTSCs in Arizona indicates that market mechanisms of transactions can be helpful in regions that need to facilitate economic growth despite water scarcity. Appendix B provides a problem structuring method for policy analysis. This article uses primary qualitative data acquired in the Fall of 2020 by interviewing sixteen 18 CAGRD experts to find alternatives to CAGRD problems. This article also produces statistical and qualitative analyses of 41 survey responses collected in the Summer of 2021 to gather Arizona stakeholder opinions about CAGRD. Results show that stakeholders' chief concerns are long-term uncertainties related to the availability of renewable water supplies and a hydrologic disconnect between the area where water is added to the aquifer and the area where it is extracted. Stakeholders' sectors and CAGRD membership influence their opinions. Potential policy changes are offered to address problems identified by stakeholders. This research will inform forthcoming policy examinations regarding groundwater management in Central Arizona as the state's decision-makers look to improve CAGRD in the context of water scarcity exacerbated by climate change. Appendix C offers methods to monitor contaminants of emerging concern in municipal wells. This article generates two simple hydrological models to estimate the impact of effluent reuse through MAR with municipal water. It uses the City of Goodyear, AZ, as its case study. This research relies on secondary data obtained from a worldwide literature review and ADWR data. Two contaminant removal models were designed to run recharge scenarios for eight municipal wells. Estimated concentrations of carbamazepine and sulfamethoxazole in municipal water were found to be below the acceptable human daily intake. This article concludes that MAR of effluent in Goodyear is effective in significatively removing these contaminants. This research has applications to other regions that recharge effluent in alluvial aquifers.