Hydrogeologic Investigations for the Tonopah Desert Recharge Project
M&A’s long-term technical support results in the permitting and successful operation of the largest recharge facility in Arizona.
Client: Central Arizona Water Conservation District (CAWCD) - Time frame: 2000–2009
- Location: Lower Hassayampa Basin, Western Arizona
The CAWCD manages the CAP, which conveys water from the Colorado River to users in central and southern Arizona. Because Arizona’s allotment of CAP water historically exceeded customer demand, the CAWCD hired M&A to investigate the feasibility of storing surplus water underground, where it would be available for future recovery during times of shortage.
M&A has been involved in many phases of this project. Beginning in 2000, we investigated six groundwater basins in western Arizona to determine the suitability of artificially recharging 200,000 to 300,000 AF/yr. After completing these reconnaissance-level investigations, we conducted technical feasibility studies for selected sites, identifying the most favorable ones for recharge based on a range of criteria.
The CAWCD selected the Tonopah Desert site, located about 50 miles west of Phoenix, as the highest priority. M&A subsequently provided technical services for the design and permitting of the recharge facilities. We also prepared a preliminary design for recovery facilities at the Tonopah Desert site.
Services
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Analyzed regional hydrogeologic conditions, including geologic structure and stratigraphy, groundwater flow, and water quality
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Characterized the lithologic conditions and infiltration capacity of near-surface soils using data collected during trenching and infiltration testing
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Characterized hydrogeologic conditions in the vadose and saturated zones using data collected during exploration drilling and sampling
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Installed monitoring wells, conducted pumping tests to estimate aquifer hydraulic properties, and collected samples to document pre-recharge groundwater quality
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Worked with the client and its engineering consultant to develop a conceptual design for the recharge facility
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Prepared a preliminary wellfield design for recovering stored water
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Estimated capital, operation, and maintenance costs, and optimized the design to minimize these costs
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Modeled the effects of full-scale recharge operations on groundwater levels to project the maximum “area of impact” and the transport of selected chemical constituents
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Revised the model to evaluate the possibility of recharge-induced flushing of nitrates from the vadose zone
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Conducted pre-application meetings with ADWR
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Prepared an application for a Underground Storage Facility (USF) permit, with supporting hydrogeologic reports, monitoring plans, and contingency plans
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Designed and installed an automated data-acquisition and telemetry system to monitor groundwater levels in wells and piezometers
Outcome
The USF permit allows the CAWCD to recharge up to 150,000 AF in any given year, with a limit of 2 MAF over 20 years.
The Tonopah Desert facility has the largest permitted capacity of any recharge project in Arizona. Recharge operations, which began in January 2006, have demonstrated that the facility is capable of storing the maximum permitted annual volume.
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