FLORIDA GEOLOGICAL SURVEY


 Figure 34 shows some geologic and hydrologic conditions in the Oak
Grove area. The beds of clay and sandy clay have been classed as rela-
tively impermeable beds. The beds of sand, sand and gravel, and gravel
have been classed as relatively permeable beds. In the vicinity of wells
054-726-1 and 2, ground water is recharged from local rainfall. Most of
this recharge moves northward and seeps into Pine Barren Creek. Some
of the recharge percolates downward to the lower permeable zone.
Ground water in this lower permeable zone may also seep into Pine
Barren Creek or move southward and discharge into other streams.
 The water level in well 054-726-2 is generally from 14 to 18 feet
higher than the level in well 054-726-1. Thus, water in the upper perme-
able sands has the head potential to recharge the lower permeable sands.
The water level in the upper sands shows more response to high rainfall
than that in the lower sands.
 The Floridan aquifer is recharged by rain in areas where the lime-
stones outcrop in Conecuh, Escambia, and Monroe counties, Alabama,
10 to 35 miles north of the area. The upper limestone of the Floridan
aquifer probably is recharged also by percolation from the sand-and-
gravel aquifer in the northern half of the area. The aquifer is discharged
by seepage into the Gulf, upward and downward leakage, and pumping.

 GROUND-WATER VELOCITIES
 The rate of ground-water flow depends upon the slope of the water
surface, the permeability of the aquifer, and the temperature of the
water. A knowledge of the rate of ground-water flow is useful to deter-
mine how fast and how far contaminated ground water will move, to
predict future areas of salt-water encroachment, and to evaluate the
effectiveness of clay beds as aquicludes.
 Using the earliest water-level data available, Jacob and Cooper
 (1940, p. 50-51) computed the average ground-water velocity in the
 sands near Pensacola Bay to be 0.37 foot per day, or 135 feet per year.
 The figure given represents the velocity under natural, undisturbed
 conditions. In the vicinity of discharging wells, the velocities would, of
 course, be higher.
 The average velocity of ground water moving through an aquifer
 may be computed by the following formula:

 Tg
 V=-
 7.48 mp
 Where: V is the velocity in feet per day; T is the coefficient of trans-
 missibility in gpd (gallons per day) per foot; g is the gradient of the