GROUND-WATER AVAILABILITY IN THE ATLANTIC COASTAL PLAIN AQUIFERS OF NORTH AND SOUTH CAROLINA

The Atlantic Coastal Plain aquifer system of North and South Carolina is an important source of potable water for a growing population. The 2000 Census reported that the combined populations of Coastal Plain counties in North Carolina and South Carolina totaled nearly 6 million people with 3.2 million located in North Carolina and 2.5 million in South Carolina. The Atlantic Coastal Plain aquifer system has a large aerial extent, covering approximately 25,000 square miles in North Carolina and approximately 20,000 square miles in South Carolina. Most of the Coastal Plain is underlain by at least one and in some areas, several highly productive aquifers.

Saltwater encroachment is occurring in several places within the Atlantic Coastal Plain aquifers in North and South Carolina in response to the lowering of these potentiometric surfaces. Most of the onshore parts of the North and South Carolina Atlantic Coastal Plain aquifers contain freshwater (total dissolved solids less than 1,000 milligrams per liter); however, brackish water and saltwater are present in the aquifer system, especially near the coast. These brackish ground-water resources are being utilized by some communities as the cost and efficiency of desalination technology have improved.

The complicated history of water use, along with substantial areal variations in aquifer properties pose challenges for the State agencies who are charged with managing these important resources. As more users demand more water, the need for scientifically based management tools has increased. A numerical ground-water-flow model is such a tool that can be used to integrate and evaluate large volumes of ground-water data to assist in the management of these important ground-water resources.

The steady-state model consists of 16 layers and composed of 130 rows by 275 columns of 2-square-mile grid cells. Net recharge, upper Coastal Plain rivers, and numerous wells are simulated as fluxes within the model. Model calibration criteria include predevelopment water levels and synoptic water levels for the study area collected in 1980, 1982, 1989, and 2004. Analysis of the baseflow of selected upper Coastal Plain streams using hydrograph separation techniques also are being used to constrain the model solutions.