Water and Land Uses:
Use of Alternative Aquifers for Supply and Wastewater Management

As previously mentioned, increased withdrawals and substantial land-use changes have adversely affected the balance between freshwater and saltwater in the surficial aquifer system in southeastern Florida. Mitigation of an aquifer contaminated with saltwater is costly, difficult, and achieved only after a lengthy period of time. Some well fields have been consolidated, some coastal well fields have been abandoned, and others have been constructed farther inland accompanied by the adoption and enforcement of wellhead protection plans. Construction of additional municipal well fields in the western part of the urban corridor, however, is ultimately limited by competing supply needs of agriculture, the Everglades ecosystem and water-conservation areas, and expanding mining interests. Alternate sources of water and effective means of storage have been of critical interest to resource managers.

Experimental freshwater aquifer storage and recovery (ASR) systems were first constructed in Miami-Dade and Palm Beach Counties during the 1970s; the Boynton Beach ASR facility represents the first operational system (1992). Most existing southern Florida ASR wells are completed in the Upper Floridan aquifer, which is the upper of two regional aquifers that form the extensive carbonate Floridan aquifer system and that underlies the intermediate confining unit (fig. 6). By the end of the 20th century, ASR was being evaluated to meet growing urban, agricultural, and ecosystem supply demands (Fies and others, 2002; Reese, 2002). Five new systems were under operational testing by 2000, and a network of 330 large-capacity ASR wells for restoration purposes was being evaluated as part of the Comprehensive Everglades Restoration Plan (CERP) (U.S. Corps of Engineers and South Florida Water Management District, 1999; National Research Council, 2001; 2002). Considerable scientific, engineering, and cost-related feasibility issues must be resolved, however, and it is uncertain whether an ASR infrastructure of unprecedented scale can meet ecosystem restoration, agricultural, and urban needs. Pilot and regional studies have been initiated to characterize the regional hydrology and geologic framework, assess the potential impact on the regional ground-water flow system (fig. 26), characterize biogeochemical reactions, and examine ecosystem sensitivity to recovered water (Fies and others, 2002; U.S. Army Corps of Engineers and South Florida Water Management District, 2002; Ward and others, 2003).

Figure 26. Hypothetical aquifer storage and recovery (ASR) pressure buildup in the Upper Floridan aquifer using the Hantush-Jacob (1955) analytical model, assuming (A) relatively high transmissivity and confining bed leakance or (B) relatively low transmissivity and confining bed leakance. This analytical model can be used to bracket uncertainty associated with large-scale head buildup using a known range of Upper Floridan aquifer hydraulic parameters. Although not mechanically possible, it was assumed that 1 billion gallons of water could be injected into three wells located about 12 miles apart for a time period of 180 days and one for a period of 2.5 years. Steady-state conditions were achieved in 180 days. The Hantush-Jacob analytical model greatly simplifies potential hydraulic responses within the Upper Floridan aquifer; however, the model can be used to assess the relative impact of likely range aquifer and confining unit hydraulic parameters including transmissivity (T=10,000 to 100,000 square feet per day), time (t=0.5 and 2.5 years), storage (S=0.0005), underlying confining unit leakance (K’/b’=0.01 to 0.0001 day-1), and discharge (Q=3.33 x 108 gallons per day per well). This example illustrates sensitivity to water-level changes in terms of uncertainty is ASR storage zone hydraulic parameters. From L.C. Murray, U.S. Geological Survey (written commun., 2002) and Fies and others (2002). [larger version]

Utilization of water withdrawn from the Upper Floridan aquifer for public-supply purposes is limited by salinity that exceeds U.S. Environmental Protection Agency (1999) secondary drinking-water standards. Reverse-osmosis treatment of Upper Floridan aquifer water for municipal use represents a growing water-supply trend, particularly in Palm Beach County, which is projected to have a public-supply demand of 338 million gallons by 2020 (Marella, 1992). Palm Beach reverse-osmosis production wells that obtain water from the Upper Floridan aquifer have been constructed in Highland Beach, Jupiter, and Tequesta (fig 15D). Reverse osmosis also is used in Broward County to treat Upper Floridan aquifer water for the city of Hollywood.

Historically, the cost of treating wastewater effluent in southeastern Florida was accompanied by concern that an expanded system of ocean outfalls would degrade coastal beach areas. Such concern in the 1970s contributed to public acceptance that deep well injection represented the preferred wastewater-management alternative (Garcia-Benochea and others, 1973). First applied in Broward County in 1959 (Hickey and Vecchioli, 1986), the disposal of liquid wastewater into saline carbonate rocks by deep well injection was used increasingly during the latter half of the 20th century for municipal and industrial wastewater and for disposal of reverse-osmosis concentrate. More than 20 Class I injection municipal and industrial facilities were operating in Palm Beach, Broward, and Miami-Dade Counties by 2000, injecting treated wastewater into the highly permeable Boulder Zone of the Lower Floridan aquifer at depths of 2,000 to 3,000 ft below NGVD 1929. In recent years, however, deep well injection has received considerable scrutiny because of the uncertain efficacy of overlying confining units and the reported upward leakage of effluent that has been observed in some monitoring wells.