Distribution of Recharging and Vulnerability of the Tertiary Limestone Aquifer, South Carolina: Regional Gradients and Important Outliers

Abstract

The distribution of ground-water radiocarbon ages from the Tertiary limestone aquifer (includes the Floridan aquifer) in South Carolina shows both a typical trend for a regional sedimentary aquifer plus a less commonly reported occurrence of disjunct outliers of recharging and thus high vulnerability to contamination located farther down the regional flow system. The main recharge area, and thus high vulnerability, is apparently in the updip Tertiary sand aquifers of the upper (inner) coastal plain that receive recharge directly and only later deliver this as ground water to the limestone formations by lateral coastward flow. In places, a considerable degree of isolation ("confinement") and protection is achieved by the time and location that this flow reaches the sand-to-limestone lateral transition near the outer (seaward) edge of the inner coastal plain. A substantial to high degree of isolation and protection is achieved or maintained in the limestone aquifer in a large part of the middle and lower coastal plain, basically where the Cooper marl and related confining layers occur. Notable exceptions exist though even within these downflow areas. Recharging and thus high vulnerability occurs in large or small-but-intense areas isolated within interior and coastal portions of the middle and lower coastal plain.