Fast-growing population centers of the state of Florida, mainly in coastal beaches, have imposed large demands on the sources of fresh water. They also threaten to deteriorate the esthetic and recreational value of the area with their waste waters.

The largest of these population centers is on the southeastern end of the peninsula of Florida, commonly referred to as the Miami area. The second largest is on the central west coast of the peninsula in the Tampa-St. Petersburg area.

The Florida peninsula is underlain by several thousand feet of carbonate rock, with only minor amounts of clastic sediments. Cavernous limestone and dolomite aquifers at relatively shallow depths constitute the principal source of fresh water in the area. Deeper cavernous zones, separated from the freshwater zones by practically impermeable limestone and dolomite, are uniquely suited to receiving injected fluids.

Deep-well disposal of waste waters into deep saline aquifers, after secondary biologic treatment and disinfection, is feasible if (1) an aquifer exists that can accept treated waste waters without significant changes in its hydraulic and structural characteristics, and (2) if use of the water in that aquifer, adjacent ones, or from surficial sources is not impaired.

Two large disposal wells have been constructed for a private utility in the Miami area of southeast Florida. They are approximately 3,000 ft in depth and recharge an artesian aquifer having chloride concentrations near that of seawater (19,000 mg/l). The receiving aquifer is overlain by a thick aquiclude, by another aquifer (saline but of lower chloride concentration), and then by a thick, impervious section separating the highly mineralized waters from the shallow and fresh groundwater.

Three concentric steel casings, cemented at the proper depths, permit injection into the deeper aquifer with protection of the upper strata. Monitoring of the upper saline water-bearing stratum, where any possible leak from the deeper aquifer would normally be first detected, is performed through the annulus between the 2 inner well casings. An integrated water-quality aquisition system continuously monitors the injected waste and provides an alarm and pump shut down if established limitations are exceeded.

Operation of the first well for over a year has proved fully reliable, and economically advantageous. Eight similar disposal wells are being considered in the area.

On the basis of this experience, a new research program is being implemented to inject, store, and recover when needed, rainfall runoff into the deep saline aquifers of southern Florida.

A test-prototype well is presently being constructed within the city of St. Petersburg to determine (1) the characteristics of the deep underground formations; (2) the quality of the deep groundwaters; (3) the injection rate capacity and associated increase in pressure; (4) the ratio of the amount of fresh water that could be subsequently recovered to that injected; and (5) the quality of the recovered water.

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