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1Publication authorized by Director, U.S. Geological Survey. Manuscript received, March 17, 1972.
Thanks are especially due to William R. Royal of Nokomis, Florida, for measuring the discharge of water and for taking the underwater photograph of the discharge section of the cave at 220 ft below water surface in Warm Mineral Springs sinkhole. Robert E. Hill of Meritt Island, Florida, collected water samples in the cave. John K. Stamer, U.S. Geological Survey at Tampa, made onsite analyses of ephemeral water-quality constituents and aided in measurement of discharge from the surface stream at Warm Mineral Springs. Charles A. Appel aided in continuous collection of data during a 2-week period when Serio No. 1 was being drilled through the “Boulder Zone” at Forty-Mile Bend.
Some of the data in the report were supplied by the California Co., Gulf Oil Corp., Humble Oil Co., and Sun Oil Co., and their cooperation is appreciated. Additional information on oil-exploratory wells was obtained by inspection of data on file at the Florida Bureau of Geology through the courtesy of Robert O. Vernon, formerly director of the Bureau and now director of the Division of Interior Resources of Florida. Data in the reports by Vernon and by J. I. Garcia-Bengo-chea were adopted and used freely, even though with different interpretation in places. The value of their observations cannot be overstated. Joseph E. Banks of Coastal Petroleum Co. supplied much data over the years, and his observations about the geology, oil, and water of Florida have invariably been stimulating. Jeff Hilleke, Larry Farnell, Lee Miller, and James Edwards, research assistants at the University of Alabama, and John McDonald, assistant professor of mechanical en-gineering, contributed greatly to the conducting of the hydraulic-model experiments and to the theoretical studies.
2Head, Department Civil and Mineral Engineering, University of Alabama.
3Staff Hydrologist, U.S. Geological Survey.

Abstract

In recent years, considerable interest has been focused on deep saline aquifers as reservoirs for the disposal of liquid waste. In general, the water in such aquifers is already in motion, being controlled by three sets of gradients: the hydraulic-pressure gradient, the geothermal gradient, and the salt-concentration gradient. In thick aquifers, interaction of these gradients may induce gravity convection currents which are not generally present in shallow constant-density fluid systems. The fate of the waste liquids entrained in such aquifer systems will depend, among other things, upon the state of motion in the aquifer before injection and the modification of this state by the injection process.

The Floridan aquifer underlying peninsular Florida is more than 2,000 ft (610 m) thick and provides a field situation for comparison with mathematical and hydraulic models. The aquifer is exposed to cold seawater where truncated by the deep trenches of the Gulf of Mexico and the Florida Strait. Natural upwellings of warm saline water and observations of temperature and salinity in wells suggest that the seawater flows inland at depth then upward into shallow parts of the aquifer, and, after mixing with fresh water, it flows seaward again to form a large, geothermaHy heated, convective flow cycle.

To develop predictive techniques for injection of waste into the deep part of this massive aquifer, a hydraulic sand model was built to simulate a saline aquifer, a geothermal source, freshwater recharge, and waste-injection wells. The studies show stream lines, velocities, and temperature/salinity distributions. The governing equations—namely, the hydraulic-flow equation, the diffusion equation for salt and injected contaminants, and the heat-diffusion equation—are solved simultaneously on a high-speed digital computer. Obtaining theoretical solutions comparable to the model data requires choosing correct empirical values of coefficients of salt and heat diffusion.

At the time of this writing, theoretical solutions have been obtained for the hydraulic model which qualitatively bear a remarkable correspondence to observed distributions of temperature and salinity in the Floridan aquifer. Work is progressing to obtain quantitative correspondence to the field observations and to extend the predictive techniques to solutions of practical problems of waste injection.

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