Home >Introduction - Purpose/Scope - Classification/ Characterization of Salinity - Inventory of Well Data - Previous Studies Hydrogeology of the Floridan Aquifer System Collection and Analysis of Salinity Data Evaluation of Formation Salinity Distribution of Salinity in the Floridan Aquifer System Origin of Salinity Summary and Conclusions References Cited Appendix: Inventory of Wells PDF Version

Introduction

The growing population of southeastern Florida (fig.1) in recent years has local and state officials concerned with finding a supplemental source for public-water supply. The virtually untapped Floridan aquifer system can be used to assist in this need. Three methods regarding its use are currently being explored: (1) blending brackish ground water from the Upper Floridan aquifer with freshwater from the overlying Biscayne aquifer in the surficial aquifer system, (2) temporarily storing excess fresh surface water or Biscayne aquifer water in the Upper Floridan aquifer and withdrawing the water when needed, and (3) treating Upper Floridan aquifer water directly by the reverse osmosis method or other desalination method. In the reverse osmosis method, high pressure is applied to the water being treated, forcing pure water through a semipermeable membrane and leaving behind the dissolved salts. Because the salinity of water in the Upper Floridan aquifer is considerably less than that of seawater, the expense of reverse osmosis treatment is also less.

The Miami-Dade Water and Sewer Department plans to construct a new Biscayne aquifer well field (West Well Field) and is considering constructing wells for water-supply augmentation at this site from the Floridan aquifer system using the above methods. Several wells completed in the Floridan aquifer system have been drilled in southeastern Florida in recent years to supply reverse osmosis treatment plants. However, before use of the Floridan aquifer system can be implemented on a large scale in the area, the distribution and controls on the quality of water in the aquifer system need to be characterized and better understood.

Figure 1. Location of the study area, wells penetrating in the Floridan aquifer system used in the study, and geologic section lines. [larger image]

To address these information needs, the U.S. Geological Survey (USGS), in cooperation with the Miami-Dade Water and Sewer Department and the South Florida Water Management District, conducted a study from May 1990 to September 1992 to: (1) describe the vertical and areal variations in water quality in the Floridan aquifer system, and (2) relate these variations in water quality to the local hydrogeology. The study area includes Dade, Broward, and parts of Monroe and Collier Counties including the upper Florida Keys (fig.1). Dade and Broward Counties bounded by the Atlantic Ocean to the east and Monroe and Collier Counties to the west. Land-surface elevation in the study area is generally less than 15 ft and averages 5 to 10 ft.

Water in the Upper Floridan aquifer in southeastern Florida is brackish with chloride and dissolved-solids concentrations generally greater than 1,000 mg/L (Sprinkle, 1989, pls. 6, 8). Salinity in the Upper Floridan aquifer usually increases with depth. The Lower Floridan aquifer contains water with a salinity similar to that of seawater (Meyer, 1989, fig. 3). Parts of the Floridan aquifer system where water has dissolved-solids concentrations less than 10,000 mg/L are to be protected from contamination by injected wastewater through the Underground Injection Control Program of the Safe Drinking Water Act (Fetter, 1988, p. 459). Underground injection control in Florida is regulated by the Florida Department of Environmental Protection (FDEP), formerly known as the Florida Department of Environmental Regulation (1982).