Little of the CAP water recharged in TAMA so far has been pumped for use, although the City of Tucson is constructing a wellfield to allow recovery of water stored at the Central Avra Valley Storage and Recovery Project (CAVSARP) in the near future. Generally, recovery of recharged water is permitted if it is recovered in the area where the water was originally stored, or in an area to which it migrated after storage. Recovery of water outside this “area of impact” is permitted under certain conditions to ensure that recovery of water does not occur in areas with substantially declining groundwater levels.

Figure 3-11 is a map of existing and proposed direct recharge facilities in TAMA. Four direct recharge facilities are currently operating in TAMA. These include CAVSARP, Pima Mine Road Recharge Project, Avra Valley Recharge Project and Sweetwater Underground Storage and Recovery Project. All of these projects utilize off-channel spreading basins to recharge CAP water, except the Sweetwater facility, which uses basins to recharge reclaimed effluent.

Figure 3-9 The Pima Mine Road recharge basins. Photo: Central Arizona Water Conservation District.

Figure 3-10 shows the amount of water stored at direct recharge facilities over time. The amount of water stored at Tucson area projects is small compared to the total renewable supplies available. Not including CAP water used at groundwater savings facilities, about 7,800 acre-feet of CAP water was recharged in TAMA in 1997, compared to approximately 215,000 acre-feet of CAP water available under sub-contract to entities in TAMA.

Figure 3-10 CAP water deliveries to direct recharge projects in the Tucson AMA.Source: Central Arizona Water Conservation District.

Direct injection is the most certain method of recharge because water can be directed to a specific location within an aquifer. For this reason, local recharge experts believe that direct injection may be the most effective tool in mitigating subsidence. With direct injection, water can be added as close as possible to the layers of the aquifer that are being compacted. The extent to which subsidence can be limited with this method, however, is uncertain, depending in part on the type of aquifer materials. Tucson Water stored approximately 4,000 acre-feet of CAP water using two pilot injection wells in 1993 and 1994. The Water Consumer Protection Act, however, allows direct injection only if the water meets or exceeds the water quality of Avra Valley groundwater in terms of hardness, salinity and dissolved organic materials and is free of disinfection by-products. Costs of treating CAP water to the Avra Valley groundwater standards would be prohibitively expensive. Entities in the Tucson area other than Tucson Water are not bound by WCPA but have not attempted direct injection.

Figure 3-11 Existing and proposed direct recharge projects.Source: Arizona Department of Water Resources

New direct recharge projects are being planned. (See Figure 3-11.) A facility permit has been issued for the Lower Santa Cruz Replenishment Project, which is projected to have a capacity of 12,000 to 13,000 acre-feet in its first phase. The facility will be located along the Santa Cruz River in northern Avra Valley. The proposed Cañada del Oro Recharge Project could add another 30,000 acre-feet of direct recharge capacity in northwest Tucson near the Town of Oro Valley. A study of the technical feasibility of the project is currently being conducted. Total direct recharge capacity on non-Indian land in TAMA is projected to be 49,000 acre-feet in the year 2000, possibly rising to 131,000 by the year 2007 with the addition of a full-scale Lower Santa Cruz Replenishment Project, the Cañada del Oro Project and expansion of existing projects to full-scale. Proposed recharge projects on Indian land could add up to an additional 41,000 acre-feet of direct recharge capacity b y 2007.