Well Rehabilitation Method to Enhance Recharge Capacity of Storage and Recovery System in Fractured Rock Aquifer

The SR 260 well field was developed by Arizona Department of Transportation (ADOT) within fractured granitic bedrock near Payson and is being used as a source of water for roadway construction activities along SR 260 between Payson and Heber, Arizona. A groundwater flow model based on discrete fracture flow predicted that the water levels in the well field would decline significantly during the life of the project and potentially impact the existing wells in nearby communities of Diamond Point and Lions Spring and nearby springs and creek, unless significant recharge occurred.  Therefore, construction of an underground water storage and recovery system to recharge surface water into the well field was deemed a viable option.  During winter months (December through April), water is being extracted from Tonto Creek, piped to the well field, and injected into the aquifer through injection wells. The construction of SR 260 was initiated in 2001 and progressed for five years with an adequate supply of construction water from the hard rock aquifer, supplemented with recharge of surface water. During the five years the system was operated, the combined injection rate of the injection wells decreased from approximately 260 gallons per minute (gpm) to less than 100 gpm.  Well rehabilitation work was performed in both injection and recovery wells in the well field in three separate work phases.  Phase 1 included recovery and injection well disassembly, water quality and scale sampling and testing, and downhole video analyses.  Phase 2 involved mechanical cleaning, and Phase 3 involved chemical treatment and pump testing of the wells. The rehabilitation work resulted in an estimated 65 percent increase in recharge capacity.