126 REPORT OF INVESTIGATIONS NO. 50
was in very salty water (more than 5,000 ppm chloride) at 1,200 feet below msl.
The chloride content of water from a nearby well was about 300 ppm at a depth of 600 feet. This concentration exceeds the U. S. Public Health Department's standards for public water supply (250 ppm chloride) and the well was destroyed. Other wells in the well field were in fresh water to depths of 700 feet or more.
It appears that the areas of salt-water contamination are to some degree, controlled by the permeability of the rock and the rate at which water can move through and flush out the salty water.
In general, salty water is found at shallower depths east of the Cocoa well field and probably at greater depths to the west. In the Orlando area, there is no salty water to a depth of at least 1.500 feet (the deepest known water well). It is not known where the salty water in the aquifer wedges out between the Cocoa well field and the City of Orlando because there are no deep wells in this area.
When a well is pumped, water moves toward the well from all directions. If the well casing extends into the aquifer, the water that is slightly above the bottom of the casing can move into the well most easily because it is assisted by gravity; however, a well also draws water from below the bottom of the casing and to some extent even from below the bottom of the open-hole portion of the well. If salty water is present below the bottom of a well, pumping may cause it to move upward and enter the well. If the well is shut down for an extended period, the heavier salt water will slowly settle.
The ultimate extent of the zone of influence caused by pumping the well depends upon the rate of pumping, the permeability of the aquifer and the recharge. The well will obtain its water from the most readily available source; therefore, if a well is pumped at a moderate rate, most of the water will come from the area above or at the same altitude as the openhole part of the well. However, if the well is pumped heavily, a larger percentage of the water will come from below the bottom of the well. Surging action in the aquifer also tends to increase salt water movement. Therefore, in areas where salty water is known to exist at depth in the aquifer, wells should be as shallow as practical and be pumped as continuously as possible at moderate rates to minimize the danger of salt-water encroachment. Wide spacing of wells will also