For more information, see http://sofia.usgs.gov/sfrsf/rooms/ hydrology/ASR

The technique pumps freshwater underground through wells into brackish-water aquifers where it forms a bubble around the wells and can be pumped out when needed. The U.S. Army Corps of Engineers' Everglades restoration plan (the Restudy) calls for capturing surface water that is now discharged into the Atlantic Ocean and Gulf of Mexico during the wet season, pumping it into limestone quarries and aquifers, and retrieving more than 1.6 billion gallons per day during the dry season. The project could provide major benefits to environmental, agricultural, and urban users. An estimated 80 percent of the retrieved water is slated to help restore the Everglades ecosystem. The technology requires a minimal amount of land (an acre or two per well) and there is almost no evaporation or seepage loss. The method has been proven at Boynton Beach, Florida, where up to 95 percent of the stored water was recovered. These advantages translate into significantly lower costs per gallon of water stored. The Corps' Restudy proposes 300 to 330 Aquifer Storage and Recovery wells. The water will be treated if necessary to meet state and federal standards for underground injection.

The hydrogeologic characteristics of a successful storage zone include moderate permeability, confinement above and below by low-permeability sediments, and water quality as fresh as possible to minimize mixing with the surrounding brackish water. The Floridan aquifer system in south Florida contains suitable storage zones, making the technology a viable storage mechanism. However, using the technology on the scale called for in the Corps's proposal is unprecedented. Uncertainties include compatibility of the injected water with the aquifer water; effects of large volumes of injected water on the confining unit; recovery efficiency, i.e. how much usable water will be recovered; and the effects of the recovered water on the environment.

To address these technical and regulatory concerns, a phased approach is proposed that will use several techniques to evaluate the feasibility and identify possible problems and solutions. Storage zones and confining units will be identified by using electronic probes lowered into drilled boreholes to measure hydrogeologic properties with depth. Detailed water-quality analyses of the water to be stored and the native (brackish) water will identify and quantify constituents of concern. Geochemical modeling may then be conducted to determine if adverse chemical reactions might occur, such as reactions that might cause plugging of the storage zone.

Ground-water modeling will be used to optimize the location and spacing of wells to minimize excessive water level drawdowns or pressure build up. In addition, modeling can be used to estimate the movement of injected water within the aquifer system and thus predict the amount and quality of recoverable water. A variety of hydrogeologic, hydrologic, and hydrochemical questions must be answered before a truly regional Aquifer Storage and Recovery infrastructure can be developed. The proposed pilot facilities - and the science necessary to evaluate the data from these - will be crucial to evaluate the feasibility and effectiveness of this technology as a regional water-storage option.