thickness of the surficial aquifer system is typically less
than 50 feet, but thicknesses of about 60 feet have been mapped
for the system in southeastern Georgia. The system generally thickens
surficial aquifer system consists mostly of beds of unconsolidated
sand, shelly sand, and shell. In places, clay beds are sufficiently
thick and continuous to divide the system into two or three aquifers;
mostly, however, the system is undivided. Complex interbedding of
fine- and coarse-textured rocks is typical of the system.
rocks that comprise the surficial aquifer system range from late
Miocene to Holocene in age. In Georgia and South Carolina, unnamed,
sandy, marine terrace deposits of Pleistocene age and sand of Holocene
age comprise the system. These sandy beds commonly contain clay
water in the surficial aquifer system is under unconfined, or water-table,
conditions practically everywhere. Locally, thin clay beds create
confined or semiconfined conditions within the system. Most of the
water that enters the system moves quickly along short flowpaths
and discharges as baseflow to streams.
places, some water leaks upward from the underlying Floridan aquifer
system through the clayey confining unit separating the Floridan
and surficial systems. In other places, where the hydraulic head
of the Floridan is lower than the water table of the surficial aquifer,
leakage can occur in the opposite direction.
the surficial aquifer system extends seaward under the Atlantic
Ocean, saltwater can encroach into the aquifer in coastal areas.
Encroachment is more extensive during droughts because there is
less freshwater available in the surficial aquifer system to keep
the saltwater from moving inland.