USGS Groundwater Information
Technical Considerations for a Large Network of ASR wells in the Comprehensive Everglades Restoration Program
By Robert A. Renken1, Michael W. Fies2,
and Shawn B. Komlos3
The feasibility of constructing and implementing a network of large-capacity aquifer storage and recovery (ASR) wells is being evaluated as part of the U.S. Army Corps of Engineers (USACE) and South Florida Water Management District's (SFWMD) $7.8 billion Comprehensive Everglades Restoration Plan (CERP). CERP represents the world's largest ecosystem restoration project attempted to date. ASR is an integral part of proposed storage features, and is the subject of pilot testing and a regional feasibility study to determine its ability to reduce water-supply competition during periods of drought. Successful implementation of the $2 billion CERP ASR program depends heavily on a multidisciplinary approach to technical investigations. The proposed ASR project will involve injecting up to 1.6 billion gallons per day of treated surface water into the slightly saline Upper Floridan aquifer during southern Florida's summer wet season. During dry, winter seasons, stored water will be recovered for delivery to sustain the aquatic and semiaquatic Florida ecosystems while still helping to offset the growing urban and agricultural water-resource demands on regional water resources. Regional ASR also will be used to maintain stage levels in Lake Okeechobee and to minimize large surface-water flows to estuaries during periods of high rainfall. About 330 dual-purpose wells, with depths ranging from 600 to more than 1,000 feet, will be required for full successful implementation.
An ASR Issue Team, formed in September 1998 under the auspices of the South Florida Ecosystem Restoration Task Force, identified several critical uncertainties associated with implementing ASR on the scale proposed by CERP. Technical concerns were raised about the proposed use of ASR that relates to its unprecedented scale. Regional issues include the need to supplement relatively scarce subsurface information in areas where ASR wells will be located, and the effect on other Upper Floridan aquifer users by the incremental hydraulic head changes from the regional ASR well network. Water-quality issues include the need to characterize suitability of surface source waters for recharge to minimize extensive pretreatment, potential environmentally deleterious water-quality changes during storage in the aquifer, and concerns that recovered water quality could pose environmental or health concerns. The length of time that the surface source water remains in storage, and whether it could affect the water quality and result in lower recovery rates is also unknown. Local performance issues include the need to determine whether the proposed ASR injection volumes will result in pressures sufficient to fracture rock, and thereby alter the hydraulic properties of storage zones, as well as overlying and underlying confining units. Additionally, there is a lack of information concerning the relations among ASR storage zone properties, recharge volumes, and whether operational efficiency can be achieved to meet projected levels. Biochemical and ecotoxicological uncertainties add further complexity to evaluating overall ASR program feasibility. Biochemical and ecotoxicological concerns include the possibility of radionuclide release, increase in methylmercury bioaccumulation in the recovered water, and uncertainties associated with the survival, attenuation, and transport of pathogens during storage or recovery of partially untreated surface water.
In George R. Aiken and Eve L. Kuniansky, editors, 2002, U.S. Geological Survey Artificial Recharge Workshop Proceedings, Sacramento, California, April 2-4, 2002: USGS Open-File Report 02-89
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