Challenge. Evaluate aquifer storage and recovery (ASR) as means of supplementing existing water supply sources to meet growing demands and during periods of drought

Solution. INTERA investigated using aquifer storage and recovery (ASR) to address three water supply options for the Guadalupe-Blanco River Authority that had firm yields ranging from 3,200 to 25,000 acre-feet/year. Based on geologic maps, subsurface cross-sections, well logs, pump test data, aquifer water chemistry, regional gradients, potential oilfield contamination, location of future demand centers, and proximity to current and planned infrastructure, we evaluated five sites for a potential ASR well field. Each of the sites was unique in relation to potential success, risks, and infrastructure development requirements. Due to the complex geology in Caldwell County, which includes numerous geological faults, steeply dipping geological formations, localized zones of contamination caused by leaking oil wells, and large contrasts in permeability among the geological formations, accurate aquifer characterization was critical to evaluating the potential ASR sites. To adequately define the highly variable hydrogeochemical conditions, INTERA analyzed over 400 geological logs, 100 aquifer pumping tests, and 200 wells with measured geochemistry to develop a geological/groundwater conceptual model for each ASR location. Where appropriate, we used results from groundwater flow models to evaluate the range of well injection and well withdrawal rates to design the ASR well network. To achieve the firm yield at each of the five sites, we developed preliminary costs for appropriate well fields, storage systems, pump stations, and conveyance pipelines. The five ASR sites were ranked in relation to each of the three water supply options, with annual costs for the options ranging from $2 to $4 per thousand gallons of water. INTERA provided recommendations for establishing ASR operations at each of the five sites that addressed issues that included permitting of groundwater wells, acquisition of future surface water permits, aquifer characterization, and ASR pilot testing.