Sustainability via Fractured Granite ASR Wells and Conjunctive Use —Payson, Arizona

Payson is a small rural mountain community located 90 miles north of the Phoenix area.  It is a popular summer retreat and therefore experiences extreme peak summer water demands.  Payson relies solely on a fracture granite aquifer for its groundwater supplies.  A new surface water source allows Payson to have access to 3,500 acre-feet per year of renewable surface water to augment its groundwater supply. 

Payson water resources professionals identified that maximizing the delivery and beneficial use of a new surface water source (“Cragin Reservoir”) would be a key element in achieving water supply sustainability.  Most importantly, aquifer storage and recovery (ASR) of Cragin water was identified as a key element in achieving sustainability while providing for operational flexibility. The challenge was implementing ASR within the environment of fractured granite aquifer hydrogeology and the subsequent integration of ASR with the town’s highly variable demand.

ASR well tests conducted by Payson with HydroSystems Inc. from 2007-2011, have proven that ASR will work in Payson’s fractured granite aquifer.  Direct correlations of an individual well’s pumping capacity to projected injection capacity were found to be unpredictable with disproportionate relationships identified, owing to the unpredictable nature of fractured ground.  In total, over 5cfs of recharge capacity has been identified to date, exceeding project goals by 100%.  Geochemical interactions of treated Cragin water within the aquifer were also investigated with no risks identified. With ASR a demonstrated success the Town may now begin to implement its plans for conjunctive use in achieving a sustainable water supply. Ultimately, excess treated surface water will be temporarily stored via selected wells which will have been converted to ASR application.  In times when municipal demands exceed surface water supply flows or when Cragin is off line, the ASR wells would automatically turn on and recover a blend of the stored surface water and groundwater for delivery.