Abstract Introduction Inventory of Data Case Studies Summary References Tables PDF Version

Aquifer storage and recovery (ASR) wells were constructed at 27 sites in southern Florida with most sites located in coastal areas. Twenty ASR were constructed by local municipalities or counties in southern Florida in the 1990's and 14 since 1996. Six of the 27 sites were experimental in nature and are no longer active. The storage zone at 23 of the 27 sites is contained within the Floridan aquifer system; of these 23 sites, 22 are in the Upper Floridan aquifer and 1 is in the Lower Floridan aquifer

Regional ASR in southern Florida has been proposed in the Comprehensive Everglades Restoration Plan (CERP) as a cost-effective water-supply alternative that can help meet needs of agricultural, municipal, and recreational users and help provide ecological benefits. About 330 high capacity wells have been proposed for southern Florida, with most to be sited inland, such as around Lake Okeechobee. Water salinity in the Upper Floridan aquifer, the hydrogeologic unit of interest in the CERP, is brackish to saline at all current ASR sites in southern Florida. The ambient salinity of water contained in the storage zone can substantially affect recovery of water recharged and stored.

This study was performed to inventory construction, hydrogeologic, and operational data on ASR sites in southern Florida and to compare site performance to hydrogeologic, design, or management factors that may influence their degree of success. Each ASR cycle includes periods of injection of freshwater, storage, and recovery, with each period lasting days or months. Potable water recovery efficiency of individual cycles at a site is the primary measure used to evaluate the performance of sites, and this efficiency is the volume of water recovered when chloride concentration reaches 250 as a percent of the volume recharged.

The basal contact of the Hawthorn Group lies close to the top of the Upper Floridan aquifer, and the most important flow zones in this aquifer commonly occur at or near this contact. The altitude of this contact varies considerably in southern Florida, ranging from less than 600 ft to greater than 1,200 ft below sea level. Local relief on this contact can be as much as several hundred feet.

Well data were inventoried and complied for all wells at existing and historical ASR sites in southern Florida. Construction and testing data were compiled into four categories: (1) well identification, location, and construction data; (2) hydraulic well-test data; (3) ambient formation water-quality data; and (4) cycle testing data. Intervals for which data were inventoried and compiled include the ASR storage zone interval and deeper and shallower intervals.

Factors important to efficient ASR operation vary widely between the sites. The thickness of the open storage zone ranged from 45 to 452 ft. Open intervals in the 150 to 200 ft range are most common. Transmissivity of the Upper Floridan aquifer storage zone for 17 sites ranged from 800 to 108,000 ft²/d. Transmissivity at the Taylor Creek/Nubbin Slough (Lake Okeechobee) site, completed in the Lower Floridan aquifer, was reported to be 590,000 ft²/d. Storage zone transmissivity for most sites ranged from 5,000 to 30,000 ft²/d; greater than 30,000 ft²/d is considered high. Leakance of storage zone confining units, determined from multiwell aquifer tests at seven sites in the Upper Floridan aquifer, ranged from 3.9 x 10^-5 to 6.3 x 10^-2 1/d; of these, five had leakance greater than 1 x 10^-3 1/d, indicating that confinement is poor in some areas. These high leakance estimates are probably best attributed to leakage from below the storage zone rather than from above. Chloride concentration of ambient water from storage zones in the Upper Floridan aquifer ranged from 500 to 11,000 mg/L. At most sites, the chloride concentration ranged from about 1,000 to 3,000 mg/L; greater than 3,000 mg/L is considered to be high.

Cycle test data were compiled for 18 ASR sites, and potable water recovery efficiencies were calculated at 16 of these sites. To date, the Boynton Beach East WTP site has experienced the highest number of recharge-recovery cycles (16 cycles). Recharge volume per cycle ranged from as low as 0.6 to as high as 714 Mgal. Cycle 3 at the Hialeah site had the longest storage time (181 days). The highest potable water recovery efficiency for the first cycle was 47 percent at the Boynton Beach East WTP site, and except for one site with incomplete information, the lowest was 2 percent at the San Carlos Estates site. Nine of the 16 sites had a recovery efficiency above 10 percent for the first cycle, and 10 sites achieved a recovery efficiency above 30 percent during at least one cycle. The highest recovery efficiency achieved was 84 percent for cycle 16 at the Boynton Beach East WTP site. Recovery efficiencies for test and operational cycles at Boynton Beach appeared to be better than all other Floridan aquifer system sites. However, the number of cycles conducted at most other sites was limited, and the chloride concentration of the recharge water used at Boynton Beach was low (about 50 mg/L).

The increase in potable water recovery efficiency during the first five cycles at the Springtree WTP site was not as favorable as at the Boynton Beach East WTP site. Recovery started at 20 percent for the first cycle and ended at 27.5 percent for the fifth cycle, despite a recharge volume for the fifth cycle (120 Mgal) that was three or more times greater than in all previous cycles. Recovery efficiencies at the Marco Lakes site for the first five cycles increased from 22 to 36 percent, with 132 Mgal recharged during cycle 5. However, these numbers may not be comparable to those from the Boynton Beach and Springtree sites because the chloride concentration of the recharged water at the Marco Lakes site was two or more times higher than at the other two sites, lowering the potable water recovery efficiencies.

Based on review of four case studies and review of data from other sites, several hydrogeologic and design factors appear to play a substantial role in the performance of ASR in the Floridan aquifer system in southern Florida. Recovery efficiency appears to be maximized if the storage zone is thin and located within the uppermost part of the Upper Floridan aquifer, and transmissivity (less than about 30,000 ft²/d) and ambient salinity (less than 3,000 mg/L chloride concentration) of the ASR storage zone are moderate. The structural setting of a site could also be important because of the potential for updip migration of recharged freshwater or the lessening of overlying confinement due to deformation. Avoiding areas that lie within a structural low or which are structurally complex or have higher dip could improve recovery efficiency.