Recharge refers to the replenishment of an aquifer's groundwater. An aquifer is a layer of underground sand, gravel, or spongy rock where water collects. Natural recharge takes place when rainfall, streamflow, or melting snow percolates into the ground.
Artificial recharge occurs when water is put into special basins or is directed into modified stream channels and allowed to sink into the ground. Artificial recharge also can take place when water is pumped directly in the aquifer through special wells.
Recharge takes advantage of water supplies available now and stores them for future use. Recharge also allows the slow introduction of new water supplies into our drinking water system by blending the new source with existing groundwater. Pilot recharge studies are done in advance of developing large-scale recharge facilities to determine recharge rates and quantities, water quality changes, the ability of the aquifer to store and release recharged water, and costs of recharging the water and pumping it for use.
The City has several recharge projects using CAP water. The Clearwater Renewable Resource Facility consists of two large recharge and recovery sites in central and southern Avra Valley. These projects are capable of recharging up to 140,000 acre-feet (46 billion gallons) of Colorado River water, nearly all of Tucson Water's current annual allocation.
The Pima Mine Road Recharge Project south of the city near the Santa Cruz River channel is a joint project with the State of Arizona, and has the capacity to store up to 30,000 acre-feet (10 billion gallons) each year.
Tucson Water also participates in several Groundwater Savings projects. These are partnerships with local farms that agree to irrigate their crops with CAP water rather than groundwater. Tucson Water sells them a portion of the City's CAP allotment at a cost that is competitive with the farmer's cost for pumping groundwater. In exchange, Tucson Water receives the right to the groundwater that would otherwise have been used. This way, the City is able to store unused groundwater for the future in much the same way that we store Colorado River water.
Recharge also helps provide treated wastewater to the City's reclaimed water system. The reclaimed water system delivers treated wastewater for irrigating parks, golf courses and schools. During months when demand for reclaimed water is low, treated wastewater is recharged in special basins near Roger Road and the Santa Cruz River, and at the City's Sweetwater Wetlands. Up to 6,500 acre-feet (2 billion gallons) of water can be held in storage each year. The water is recovered and used during the summer months and for the fall reseeding of golf courses when demand for reclaimed water is at its peak.
The City also partners with other municipal water providers - Pima County and the U.S. Department of the Interior - to manage the recharge of treated wastewater that flows into the Santa Cruz river from Pima County's Municipal Wastewater Treatment facilities. This managed recharge allows the partners to build groundwater credits that can later be used to recover either the recharged effluent for use in the Reclaimed Water system or potable (drinking) water from elsewhere in the Tucson basin.