Scientific Investigations Report 2006-5239
Prepared as part of the
U.S. Geological Survey Greater Everglades Priority Ecosystems Science Initiative
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Purpose and Scope
Hydrogeology of the Upper Floridan Aquifer
Inventory and Compilation of Well and Test Data
Construction and Testing Data
Well Identification and Construction Data
Hydraulic Well-Test Data
Quality of Ambient Ground Water
Cycle Test Data
Aquifer Storage and Recovery Performance in the Upper Floridan Aquifer
Factors Affecting Freshwater Recovery
Design and Management Factors
Analysis of Cycle Test Data at Selected Sites
Fiveash Water Treatment Plant (Site 3)
Springtree Water Treatment Plant (Site 4)
Shell Creek Water Treatment Plant (Site 6)
Marco Lakes (Site 7)
Boynton Beach East Water Treatment Plant (Site 23)
Delray Beach North Storage Reservoir (Site 24)
West Palm Beach Water Treatment Plant (Site 29)
Evaluation of Site Performance
Recovery Efficiency and Relative Performance
Hydrogeologic, Design and Management Factors
Appendix 1--Geophysical Logs and Hydrogeologic Characteristics for Selected Wells at Aquifer Storage and Recovery Sites in Southern Florida
Appendix 2--Sources of Literature for the Aquifer Storage and Recovery Sites in Southern Florida
Well construction, hydraulic well test, ambient water-quality, and cycle test data were inventoried and compiled for 30 aquifer storage and recovery facilities constructed in the Floridan aquifer system in southern Florida. Most of the facilities are operated by local municipalities or counties in coastal areas, but five sites are currently being evaluated as part of the Comprehensive Everglades Restoration Plan. The relative performance of all sites with adequate cycle test data was determined, and compared with four hydrogeologic and design factors that may affect recovery efficiency.
Testing or operational cycles include recharge, storage, and recovery periods that each last days or months. Cycle test data calculations were made including the potable water (chloride concentration of less than 250 milligrams per liter) recovery efficiency per cycle, total recovery efficiency per cycle, and cumulative potable water recovery efficiencies for all of the cycles at each site. The potable water recovery efficiency is the percentage of the total amount of potable water recharged for each cycle that is recovered; potable water recovery efficiency calculations (per cycle and cumulative) were the primary measures used to evaluate site performance in this study. Total recovery efficiency, which is the percent recovery at the end of each cycle, however, can be substantially higher and is the performance measure normally used in the operation of water-treatment plants.
The Upper Floridan aquifer of the Floridan aquifer system currently is being used, or planned for use, at 29 of the aquifer storage and recovery sites. The Upper Floridan aquifer is continuous throughout southern Florida, and its overlying confinement is generally good; however, the aquifer contains brackish to saline ground water that can greatly affect freshwater storage and recovery due to dispersive mixing within the aquifer. The hydrogeology of the Upper Floridan varies in southern Florida; confinement between flow zones is better in southwestern Florida than in southeastern Florida. Vertical hydraulic conductivity in the upper part of the aquifer also may be higher in southeastern Florida because of unconformities present at formation contacts within the aquifer that may be better developed in this area.
Recovery efficiencies per cycle varied widely. Eight sites had recovery efficiencies of less than about 10 percent for the first cycle, and three of these sites had not yet achieved recoveries exceeding 10 percent, even after three to five cycles. The highest recovery efficiency achieved per cycle was 94 percent. Three southeastern coastal sites and two southwestern coastal sites have achieved potable water recoveries per cycle exceeding 60 percent. One of the southeastern coastal sites and both of the southwestern coastal sites achieved good recoveries, even with long storage periods (from 174 to 191 days). The high recovery efficiencies for some cycles apparently resulted from water banking—an operational approach whereby an initial cycle with a large recharge volume of water is followed by cycles with much smaller recharge volume. This practice flushes out the aquifer around the well and builds up a buffer zone that can maintain high recovery efficiency in the subsequent cycles.
The relative performance of all sites with adequate cycle test data was determined. Performance was arbitrarily grouped into “high” (greater than 40 percent), “medium” (between 20 and 40 percent), and “low” (less than 20 percent) categories based primarily on their cumulative recovery efficiency for the first seven cycles, or projected to seven cycles if fewer cycles were conducted. The ratings of three sites, considered to be borderline, were modified using the overall recharge rate derived from the cumulative recharge volumes. A higher overall recharge rate (greater than 300 million gallons per year) can improve recovery efficiency because of the water-banking effect. Of the 30 sites in this study, a rating was determined for 17 sites, of which 7 sites were rated high, 5 sites were rated medium, and 5 sites were rated low.
Four hydrogeologic and design factors that may affect recovery were compared with the relative performance ratings. These factors are the thickness, transmissivity, and ambient chloride concentration (correlated with salinity) of the storage zone, and the thickness of the portion of the aquifer above the top of the storage zone. Threshold values for these factors of 150 feet, 30,000 square feet per day, 2,500 milligrams per liter, and 50 feet were chosen, respectively; each represents a value above which recovery efficiency could be adversely affected. Some general correlation of the performance ratings with the number of factors above the threshold value was found. The best correlation was found with the transmissivity and ambient chloride concentration factors, but some correlation also was indicated with the thickness of the storage zone.
Long intercycle or storage periods can adversely affect recovery efficiency. This adverse effect appears to be more likely for Upper Floridan aquifer sites in southeastern Florida than in southwestern Florida; southeastern Florida has higher ambient salinity, higher apparent vertical hydraulic conductivity, and more storage zones located greater than 50 feet below the top of the aquifer. This effect could be caused by upward migration of the recharged freshwater “bubble” during these periods as a result of buoyancy. Some evidence for this was found in the performance ratings for sites and in the analyses of certain cycles with long inactive periods.
Reese, R.S., and Alvarez-Zarikian, C.A., 2007, Hydrogeology and Aquifer Storage and Recovery Performance in the Upper Floridan Aquifer, Southern Florida: U.S. Geological Survey Scientific Investigations Report 2006-5239, 117 p. (appendixes on CD).
U.S. Department of the Interior
U.S. Geological Survey
Florida Integrated Science Center
3110 SW 9th Avenue
Ft. Lauderdale, FL 33315
Ronald S. Reese firstname.lastname@example.org
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