FLORIDA GEOLOGICAL SURVEY


 GROUND WATER
 SAND-AND-GRAVEL AQUIFER
 Although nearly all the ground water being used in Escambia and
Santa Rosa counties comes from the sand-and-gravel aquifer, the full
potential of the aquifer is not utilized. Figure 5 illustrates the general
area of potential development of ground-water in Escambia and Santa
Rosa counties. An understanding of the limiting factors is necessary if
the sand-and-gravel aquifer is to be fully utilized. The limiting factors
were considered to help designate the general areas shown in figure 5.
 Areas of abundant fresh ground water.-Large ground-water supplies
in the sand-and-gravel aquifer can be developed in the northern half of
Escambia and Santa Rosa counties. Only a minor amount of the available
ground water in these areas is being used at the present time. The thick-
ness of the sand-and-gravel deposits ranges from about 230 to almost
1,000 feet. Generally, these deposits are more than 400 feet thick. Figure
5 shows other areas where large supplies can be developed, such as
northwest of Pensacola and north of Navarre. Small or domestic supplies
of water can be developed most anywhere in the two counties except
close to the shores of the narrow islands.

 Factors which limit the amount of fresh ground water.-
 1. Concentrated pumpage: Heavy, continued pumping can cause
a cone of depression to extend a considerable distance outward from a
well field, perhaps far enough to overlap a cone created by another well
field. Both well fields then, in effect, compete for the water and the
resultant drawdown of the water level is correspondingly greater. The
areas where large supplies have been developed are shown in figure
5. Additional development in these areas should be carefully planned.
 2. Proximity to salt water: The Gulf of Mexico, Santa Rosa Sound,
and all the bays contain salty water. In addition, wedges of salt water
extend for varying distances up the streams that empty into the bays.
Where the water table has been depressed by pumping, salt water from
these sources may invade fresh-water supplies. Figure 5 shows the areas
of potential danger from salt-water encroachment.
 3. Presence of clay lenses: The sand-and-gravel aquifer contains
 lenses of clay and sandy clay which decrease the permeability of the
 aquifer. The total amount of clay is highly variable. As these clay lenses
 are relatively impermeable they limit the quantity of water that can be
 withdrawn from the aquifer at any given place.