Groundwater is part of the water cycle (Figure 1). A portion of precipitation that lands on the ground moves downward through the ground until it reaches a saturated zone (every opening such as space between grains of sand or every fracture in the bedrock) that is filled with water (see Figure 2).
In South Carolina, our state is divided into two distinct physical geographic regions, the Mountains/Piedmont and the Coastal Plain (see Figure 3). In the Mountain and Piedmont region of the state, groundwater occurs primarily within the fractures of rock. The shallow/water-table aquifer occurs at the transition zone between the weathered soils and the bedrock.
The groundwater aquifers of the Coastal Plain are primarily unconsolidated sediments (sands, silts, and clays) and some sedimentary rock such as limestone. Figure 4 shows a depiction of the major groundwater aquifers in the South Carolina Coastal Plain. The aquifers thicken and become deeper as you move from the boundary of the Coastal Plain and the Piedmont towards the coast.
A drinking water well that is installed in the McQueen Branch aquifer system in Lexington County might be 200-300 feet deep. A well installed in this same aquifer in Berkeley County may be as deep as 1600 feet. Near the boundary where the Coastal Plain meets the Piedmont, the shallow/water-table aquifer system may be connected to the regional aquifer system. As you move East towards the coast, this shallow/unconfined aquifer system becomes more separated from the deeper aquifers by what are called “confining units”. Confining units are zones of low permeability such as clays and silts that separate the water-bearing aquifers.