Peak daily pumpage from the highly permeable, unconfined Biscayne aquifer for public water-supply systems in southeast Florida in 1975 was about 500 million gallons. Another 165 million gallons was withdrawn daily for irrigation. Recharge to the aquifer is primarily by local rainfall. Discharge is by evapotranspiration, canal drainage, coastal seepage, and pumping. Pollutants can enter the aquifer by direct infiltration from land surface or controlled canals, septic-tank and other drainfields, drainage wells, and solid-waste dumps. Most of the pollutants are concentrated in the upper 20 to 30 feet of the aquifer; public supply wells generally range in depth from about 75 to 150 feet. Dilution, dispersion, and adsorption tend to reduce the concentrations. Seasonal heavy rainfall and canal discharge accelerate ground-water circulation, thereby tending to dilute and flush upper zones of the aquifer. The ultimate fate of pollutants in the aquifer is the ocean, although some may be adsorbed by the aquifer materials en route to the ocean, and some are diverted to pumping wells.

Attention has recently been directed to the effects of rapid growth in southeast Florida on the quality of the water in the Biscayne aquifer -- the prime source of drinking water in the area. Attendant with rapid growth has been such practices as: (1) Use of french drains and disposal wells for the discharge of some storm water and industrial wastes; (2) widespread and scattered emplacement of solid-waste disposal sites; (3) installation of thousands of septic tanks for individual residences, apartment dwellings and small industries; (4) discharge of various types of runoff or effluent into shallow soakage pits; and (5) discharge of treated and partly treated sewage effluent into controlled drainage canals and soakage pits. There has also been concern about the long-term use of fertilizers and pesticides in the agricultural areas of southeast Florida and in the urban areas where large quantities are used for lawns and gardens.

As early as 1971, the U.S. Environmental Protection Agency (EPA), became concerned over the quality of the surface water and ground water in Dade County and made an inventory of waste sources in the county. The EPA has been petitioned (in 1978) to designate the Biscayne aquifer as a sole-source aquifer (under Section 1424 E, Safe Drinking Water Act of 1974). The U.S. Geological Survey was requested by the EPA to furnish information on geology, hydrology, water quality and other data which would assist them in the decision regarding such designation of the Biscayne aquifer.

Since the late 1930’s, the U.S. Geological Survey has been involved in investigations of the water resources of southeast Florida in cooperation with Federal, State, and many local agencies. The investigations have resulted in the collection of large amounts of basic data and in numerous reports on various aspects of the hydrology of the Biscayne aquifer. This report is based on information contained in those reports and in reports by local governmental agencies and by consultants. Basic data from files of local, State, and Federal agencies were also used. No new field data were collected for this investigation.

The following factors may be used to convert U.S. inch-pound units to SI units.