Pasco ASR Feasibility Study

Competing uses for water are continuing to increase demands on surface water and groundwater resources in the Pasco Basin. In addition to these increasing demands, the City also faces constraints on developing new supply sources as it plans, develops, and maintains safe and reliable sources of water for its customers. The City would like to diversify its water supply portfolio and create a sustainable, resilient water source to help meet peak demands and future demand projections for their potable and irrigation systems. GSI is managing a feasibility study to determine the feasibility of using ASR to optimize the use of existing water rights and increase the sustainability and resiliency of the City’s water supply given that new water supply sources may not be available.

The study is evaluating the feasibility of injecting and storing water from existing supply sources in a deep aquifer system using a well or series of wells during the winter months—when water is more readily available and demands are seasonally low—and recovering that stored water using those same wells to meet peak-summer demands. This would allow the City to augment peak-season demand needs and help meet projected demand shortfalls without increasing permitted withdrawals from their Columbia River supply sources during the low-flow summer months. Work elements have included identifying the accessibility of potential ASR supply sources considering water rights and environmental constraints, characterizing local hydrogeologic conditions, identifying potential aquifer storage zones, and developing conceptual designs for injection and recovery wells.

The feasibility study is ongoing. The next phase will address hydrogeologic and water quality data gaps prior to conducting any site-specific exploratory or test well drilling investigations and will complete a preliminary water quality evaluation to assess geochemical compatibility between source water and basalt groundwater. The water quality evaluation also will include an assessment of all known, available, and reasonable methods of prevention, control, and treatment (AKART) to identify the likely best approach to reduce or eliminate constituents that might violate Washington State’s anti-degradation policy.

GSI’s work has involved:

• Identifying locations and characteristics of potential aquifer storage zones beneath the City that may be suitable for aquifer storage and recovery.
• Developing a conceptual hydrogeologic model of the aquifer system.
• Evaluating when, where, and how much source water may be available for ASR recharge, considering legal and physical water availability and water system conveyance and treatment constraints.
• Developing a conceptual ASR storage model, including storage capacity estimates, recharge/recovery well concepts, and the recoverability of stored water.
• Siting ASR wells and developing conceptual ASR well designs.
• Writing a successful grant to obtain $350,000 from the Washington State Department of Ecology for the next phase of the project.