Approximate Eastern Limit of the Gray Limestone Aquifer in Dade County, USGS WRIR 90-4108, figure 14

An aquifer identified by Fish (1988) in Broward County, composed of predominantly gray (in places, greenish-gray or tan) limestone of the lower part and locally the middle part of the Tamiami Formation, was identified at depths of about 70 to 160 ft below land surface in western Dade County. Although it is less permeable than the Biscayne aquifer, the gray limestone aquifer is still significant and is a potential source of water, particularly west of the western limit of the Biscayne aquifer. It is defined as that part of the limestone beds (usually gray) and contiguous, very coarse, elastic beds of the lower to middle part of the Tamiami Formation that are highly permeable (having a hydraulic conductivity of about 100 ft/d or greater) and at least 10 ft thick. Above and below the gray limestone aquifer in western Dade County, and separating it from the Biscayne aquifer and the base of the surficial aquifer system, are sediments having relatively low permeability, such as mixtures of sand, clay, silt, shell, and lime mud, as well as some sediments having moderate to low permeability, such as limestone, sandstone, and claystone.

Drilling has identified the gray limestone aquifer in western Broward County and in southwestern Palm Beach County; in these areas, water in the aquifer contains high concentrations of dissolved solids. The aquifer may extend westward into Collier County, and it may be the source of water for irrigation of sugarcane fields in southeastern Hendry County and domestic use on the Seminole Indian Reservation.

The map shows the approximate eastern limit of the gray limestone aquifer in Miami-Dade County.