%)9
ing wet seasons, it ordinarily cannot be stored in a confined aquifer for withdrawal during subsequent droughts.
Chemical Quality of Ground Water
At times in the geologic past the sea has stood much higher than it stands today. At those times, the salty water of the sea, under the thrust of the sea's stronger pressure, moved considerable distances into the aquifer. Some ground-water hydrologists believe that it is a consequence of this ancient invasion that the artesian water is now salty over much of Florida (see fig. 19). Since the sea was last high, possibly 10,000 to 20,000 years ago, the seaward circulation of fresh water has been gradually flushing the salty water out. Eventually the artesian water may become fresh almost everywhere, but that is too far in the future to be of much interest to us.
Over most of the State deep wells drilled for oil have penetrated very salty water, some of it much saltier than the sea, at depths of several thousand feet. We infer from this that such water may occur everywhere beneath the State, but our information is too scanty for us to be sure. Wherever it does occur, the salty water menaces the fresh artesian water that lies above, for unwise
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FIGURE 20.--Hardness of water from upper part of the Floridan aquifer.
Lines connect points of equal hardness, in parts per million.