FLORIDA GEOLOGICAL SURVEY


 GROUND WATER
 PRINCIPLES OF OCCURRENCE
 Ground water is the subsurface water in the zone of saturation, the
zone in which all pore spaces are filled with water under pressure greater
than atmospheric. Potable ground water in Escambia and Santa Rosa
counties is derived from precipitation. Part of the precipitation reaches
the zone of saturation to become ground water. Ground water in Escam-
bia and Santa Rosa counties moves laterally under the influence of
gravity from places of recharge toward places of discharge, such as wells,
springs, and surface-water bodies.
 Ground water in Escambia and Santa Rosa counties occurs undei
both nonartesian and artesian conditions. Where it is not confined, its
surface is free to rise and fall, and the water is under nonartesian con-
ditions. The upper water surface is called the water table. Where the
water is confined in a permeable bed that is overlain by a less permeable
bed, so that its water surface is not free to rise and fall, it is under arte-
sian conditions and the upper water surface in wells is called the arte-
sian pressure surface. The term "artesian" is applied to ground water that
is confined and under sufficient pressure to rise above the top of the
permeable bed that contains it, though not necessarily to or above the
land surface. The height to which water will rise in an artesian well is
called the artesian pressure head.
 An aquifer is a formation, group of formations, or part of a formation
 -in the zone of saturation-that is permeable enough to transmit usable
 quantities of water. Places where aquifers are replenished are called re-
 charge areas, and places where water is lost from aquifers are called
 discharge areas.

 HYDROLOGIC PROPERTIES OF THE AQUIFERS
 Ground water in Escambia and Santa Rosa counties occurs in three
 major aquifers: a shallow aquifer which is both artesian and nonartesian
 (the sand-and-gravel aquifer), and two deep artesian aquifers (the
 upper and lower limestones of the Floridan aquifer). In the southern
 half of the area, the sand-and-gravel aquifer and the upper limestone of
 the Floridan aquifer are separated by a thick section of relatively im-
 permeable clay; but in the northern half the sand-and-gravel aquifer and
 the upper limestone of the Floridan aquifer are in contact with one an-
 other. The upper limestone of the Floridan aquifer is separated from
 the lower limestone by a thick clay bed.