Aquifer Recharge, Storage, and Recovery - Southwest Hydrology ...

Water Spreading in the DesertMario R. Lluria – HydroSystems Inc.In the late 1980s, the portion ofthe Central Arizona Project (CAP)aqueduct that conveys water fromthe Colorado River to Phoenix wascompleted. At the time, the Salt RiverValley lacked sufficient surface storagecapacity for Arizona’s unused portionof CAP water, and storage in the distantreservoirs of the Salt and Verde rivers wasprohibitively expensive. Consequently,the Salt River Project (SRP) and severalmunicipalities agreed to develop a largeunderground water storage facility. A studyfunded by the Arizona Municipal WaterUser Association (AMWUA) identifiedfavorable sites in the Salt and Agua Friarivers for in-channel groundwater recharge,a method successfully used for manyyears in the Los Angeles Basin to storewater in the underlying alluvial aquifer.The First Facility: GRUSPIn 1986, the City of Mesa and SRPinitiated work on a large water-spreadingrecharge facility in the East Salt RiverValley. Based on the AMWUA study,SRP evaluated a 7-mile-long reachof the lower Salt River immediatelydownstream of Granite Reef Dam, andfound favorable hydrogeologic conditionswith no environmental constraints.Four potential sites were selected, allnear the SRP water delivery system andits large-capacity wells, providing thenecessary supporting infrastructure. In1987, Phoenix-area municipalities joinedwith SRP to select a site, acquire the land,and design, permit, construct, and operatethe regional Granite Reef UndergroundStorage Project (GRUSP). More than 90percent of the site would be within the SaltRiver Pima-Maricopa Indian Reservation.Negotiations with the tribal governmentconcluded in 1992 with the leasing of a350-acre parcel for a period of twentyyears. Every five years the land is reappraisedand the rent adjusted accordingto current value. The main determinant isthe value of the land’s sand and gravel,which is in high demand. Thus, a steady,substantial rent increase has affectedthe unit cost of recharge at GRUSP.The permit process for GRUSPcommenced in 1987 and was completedin 1992. Two federal permits wererequired under the Clean Water Act,one each from the U.S. EnvironmentalProtection Agency and the Army Corpsof Engineers. State permits were issuedby the Arizona Department of WaterResources (for underground storage) andthe Arizona Department of EnvironmentalQuality (for aquifer protection).Construction and OperationIn 1994, four recharge basins with a totalarea of 174 acres were completed. Twomore added in 1999 increased the areato 225 acres. Originally, CAP water andwater from the Salt and Verde rivers wereused for recharge; in 2007 reclaimedwater was added. The waters are mixedbefore entering the recharge basins.One of the most important factors inGRUSP’s successful operation is the site’sfavorable hydrogeologic characteristics.On the periphery of the large Salt RiverValley tectonic basin, the site’s coarsegrainedunconsolidated sands and gravelshave high permeability and water storagecapacity, producing recharge rates of 2 to7 feet per day. The storage capacity of thearea of hydrologic impact exceeds onemillion acre-feet. Over 920,000 acre-feetof water have been stored in GRUSP,both short-term and long-term, over its13 years of operation (Lluria, 1998).View of the Granite Reef Underground Storage facility in 1995, showingcanals transporting CAP water to the facility in the Salt River Valley.28 • May/June 2008 • Southwest Hydrology