Restrictions on surface-waste disposal practices have caused many to look to subsurface storage of liquid waste in deep saline aquifers as a most practicable and economical alternative. Also, temporary subsurface storage of excess storm runoff and treated sewage as potential sources of fresh water to augment supplies in water-short areas is being investigated. Liquid wastes are being injected into deep, saline, carbonate aquifers at sites in the western panhandle and the southern peninsula of Florida. Additional sites are being considered in the central peninsula. The wastes, including acidic, high-oxygen-demand industrial plant effluents and variable temperature and density, secondary sewage plant effluents, and oil-field brines, are injected into permeable saline zones eparated from shallower freshwater aquifers by one or more confining layers which have very little or practically no permeability. There are distinctive differences in stratigraphy between the panhandle and the peninsula of Florida. Hence, the geologic and hydrologic environments for subsurface waste storage also are different.

At a site near Pensacola, in western Florida, acidic liquid waste has, for nearly 10 years, been injected into a 1,400-1,700-ft deep, moderately permeable, carbonate zone of late Eocene age, separated from shallower freshwater aquifers by a widespread, 200-ft thick, nonpermeable, confining, plastic clay layer of middle Oligocene age. The calculated pressure effects of this injection now extend outward more than 30 mi. The

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waste has improved the permeability of the injection zone near the injection well by dissolution of the limestone. There is no evidence that the confining layer or the carbonate aquifer above this confining layer have been adversely affected by the injection.

In the south part of peninsular Florida, the saline-water-bearing parts of the thick Cretaceous and Tertiary section utilized for waste storage consist almost entirely of carbonate rocks, in part anhydritic. Nonpermeable rock separates the highly permeable, commonly cavernous, injection zones from both shallower and deeper permeable zones. Secondary sewage plant effluent has been injected for about 2 years into a very cavernous limestone of early Eocene age at a depth of about 3,000 ft in the Miami area, with only a slight bottomhole pressure increase during injection. Neither the quality of the water nor the pressure in the overlying permeable zones have been affected by the injection. Hot acidic waste injected at a depth of about 1,500 ft in northwestern Palm Beach County migrated u ward to a shallower permeable zone. The injection well was subsequently drilled deeper and cased to about 2,000 ft to confine the waste to the injection zone.

A study of the stratigraphy of south peninsular Florida has delineated 5 discrete zones of high transmissivity in cavernous carbonate beds of Late Cretaceous through Eocene age. Cavities whose maximum vertical dimensions are as great as 90 ft have been found in wells. Zones of high transmissivity are in Upper Cretaceous beds between depths of 5,000 and 6,000 ft and in Paleocene beds between depths of 3,500 and 4,500 ft. A widespread zone in the basal Eocene lies between depths of 2,500 and 3,300 ft in south peninsular Florida, and farther north a zone higher in the Eocene section is at depths of 1,500-2,000 ft. Even younger Eocene zones occur between depths of 1,100 and 1,300 ft in and north of the Lake Okeechobee area.

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