DEVELOPMENT OF A SOUTH CAROLINA SALINITY INTRUSION GROUND WATER MONITORING NETWORK

Ground water is one of the most important resources in the United States. In South Carolina, 20% of the population lives in coastal areas that depend on fresh ground water supplies for domestic, municipal, industrial or agricultural purposes. Over-pumping has created cones of depression and intercepted natural flow, causing saltwater intrusion to become a common and persistent problem for coastal areas that depend on ground water. Contamination of ground water occurs as high concentrations of total dissolved solids (specifically chloride) in dense seawater move into less dense freshwater. The seaward limit of freshwater in an aquifer is controlled by several factors including hydrogeologic setting, the amount freshwater flowing through the aquifer, proximity to tidally influenced saline water bodies, and relative densities between fresh and saltwater. Additionally, these factors can vary spatially due to ground water demand and the direction of regional ground water flow.

Salinity intrusion into the Upper Floridan aquifer along the southern coast of South Carolina has been well documented. Less is known about the current extent and range of salinity intrusion within the Middle Floridan and Black Creek aquifers along central and northern coastal South Carolina. In order to address this issue, a network of salinity intrusion wells were selected for monitoring within the existing South Carolina ground water monitoring network. Selected observation wells completed within the the Middle Floridan and Black Creek Aquifers were instrumented with water level and conductivity continuous logging data recorders, and in-situ measurements are verified by spot measurements. Using specific conductivity (µS/cm) as a surrogate for chloride concentration (mg/L) data are recorded and analyzed to estimate the landward location of the freshwater – saltwater transition zone. Network and data management, quality assurance, and documentation are integral parts of this project and allow for the reporting of reliable information. The documentation of the freshwater – saltwater interface will provide guidance for water managers and decision-makers to implement sustainable ground water management strategies that will ensure the availability of this important resource.