Regional aquifer storage and recovery (ASR) in south Florida is proposed as a cost-effective water-supply alternative that can help meet needs of agricultural, municipal, and recreational users and help provide for Everglades ecosystem restoration. In the Comprehensive Everglades Restoration Plan (CERP), about 300 ASR wells are planned in south Florida, and the estimated capacity for each well is 5 million gallons per day during injection and withdrawal, a planned ASR application much larger than any yet attempted. ASR technology has been tested and implemented in some areas of south Florida; ASR wells have been constructed at 24 sites in an area that extends southward from Charlotte, DeSoto, Glades, Okeechobee, and St. Lucie Counties, and wells are planned (or are in the permitting process) at five additional sites. A pilot ASR facility currently is under construction by the South Florida Water Management District on the Hillsboro Canal in southeastern Palm Beach County. Three ASR facilities are operational.

Existing and historical ASR sites in south Florida (fig. 1) have mostly been located along the east and west coast. At most of these sites, the recovered water is being used, or is

Figure 1. Existing and historical aquifer storage and recovery sites and study areas. Click for larger image.

planned to be used, as additional water supply for local municipalities. In the CERP wells, however, will be located in more inland area such as around Lake Okeechobee, in central Palm Beach County, and along the Caloosahatchee River in Lee, Glades, and Hendry Counties. The recovered water will be used for additional purposes, including maintaining water levels in wetland areas. Historical, current, and planned ASR sites are listed in table 1 along with aquifers being used, their status, type of source injection water, and number of wells drilled. The source water planned for the CERP ASR program is untreated or minimally treated ground water or surface water. The injection interval being used at most sites is the Upper Floridan aquifer, which is in the Floridan aquifer system, and is underlain by the middle confining unit and Lower Floridan aquifer.

Few regional investigations of the Floridan aquifer system hydrogeology in south Florida have been conducted, and these studies did not address many of the scientific issues relating to ASR. Lacking a regional ASR framework to aid the decision-making process, ASR well sites in south Florida have been primarily located based on factors such as land availability, source-water quality, and source-water proximity (pre-existing surface-water canal systems or surficial aquifer system well fields). Little effort has been made to link information collected from each existing ASR site and from other historical non-ASR wells into a regional hydrogeologic analysis. Additional tools and data are needed to make informed decisions that incorporate constraining hydrogeologic factors in the placement and construction of ASR facilities in south Florida.

Important hydrogeologic and construction related attributes are being determined for each ASR site, and these attributes are being plotted on maps for the purpose of a comparative analysis of differences between the ASR sites. Hydrogeologic attributes include aquifer transmissivity and degree of confinement, native ground-water salinity, and the structural setting of the site. Construction related attributes include placement of the injection zone relative to the top of the aquifer and the diameter and thickness of the injection zone, which in most cases, is an open hole interval below the final casing. Published hydrogeologic frameworks of the Floridan aquifer system in south Florida are being reviewed and refined in order to relate ASR well sites to a regional scale.

Historical and current data on ASR cycle testing at each site are being assembled, and the recovery efficiency, if not clearly defined or substantiated in a report, will be evaluated. The recovery efficiency will be related to the hydrogeologic and construction related attributes listed above to identify common threads, technical issues, or potential problems that have been encountered and that influence the level of success of ASR. Data collected so far indicate that some important problems are injection zones with a transmissivity that is too high due to fractured dolomite, transmissivity that is too low, ambient ground-water salinity that is too high, and casings that have been set too deep within the aquifer resulting in the loss of injected water. Sites that are located in structural depressions could also be problematic because of loss of injected water due to buoyancy effects.

(This abstract was taken from the Greater Everglades Ecosystem Restoration (GEER) Open File Report (PDF, 8.7 MB))

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