TRITIUM IN GROUNDWATER OF THE GEORGIA PIEDMONT - IMPLICATIONS FOR RECHARGE AND FLOW PATHS

Environmental tritium was measured in 33 natural water samples representative of precipitation, stream runoff, and groundwater (derived principally from production wells) within the Georgia Piedmont Province. Major ion analyses were used to assist in the interpretation of the tritium results. Tritium concentrations were significantly greater within shallow groundwater derived from the regolith (28-34 TU) and stream runoff (25-30 TU) than within recent rainfall (4-17 TU). Based upon the decay-corrected tritium input function, this probably indicates that at least some of the shallow water is stored within the regolith for a period of approximately 25 years. A 'post-bomb' component of recharge was present in all groundwater derived from production wells in the study area. Groundwater sampled from the bedrock aquifers was commonly less tritiated than either stream runoff or shallow water stored in the regolith. The lower tritium concentrations may have resulted from the mixing of 'pre-bomb' water stored within the fractures or the transitional zone directly above the bedrock and modern water stored in the shallow regolith. The preponderance of modern water provides evidence that groundwater flow paths are areally restricted within this setting, probably confined to local surface water drainage basins. The residence time of groundwater in the Piedmont is limited by the lack of deep, gravity-driven regional flow and the localized vertical flow induced by pumping. The results of this study indicate that relatively small tritium concentration variations (10-20 TU) may have regional hydrological significance in the southeastern Piedmont Province and similar settings.