Geochemistry of ground water at the Savannah River Plant

Abstract

Subsurface hydrogeologic systems underlying the Savannah River Plant (SRP) were studied to determine the origin and age of the contained fluids. Three distinct systems exist beneath SRP: the Coastal Plain sediments, crystalline metamorphic basement rock, and a Triassic rock basin surrounded by the crystalline rock. The water in the Coastal Plain sediments is low in dissolved solids (approximately 30 mg/l), acidic (pH approximately 5.5), and comparatively recent. Water in the crystalline rock is high in dissolved solids (approximately 6000 mg/l), alkaline (pH approximately 8), and approximately 840,000 years old as determined by helium dating techniques. Water in the Triassic rock is highest in dissolved solids (approximately 18,000 mg/l) and is probably older than the water in the surrounding crystalline rock; a quantitative age was not determined. The origin of the water in the crystalline and Triassic rock could not be determined with certainty; however, it is not relic sea water. A detailed geologic-hydrologic history of the SRP region is presented.