Precipitation, Ground-Water Use, and Ground-Water Levels in the Vicinity of the Savannah River Site, Georgia and South Carolina, 1992–2002

Proceedings of the 2003 Georgia Water Resources Conference, held April 23-24, 2003, at the University of Georgia.Contamination of ground water at the U.S. Department of Energy Savannah River Site has raised concern over the possible migration of waterborne contaminants beneath the Savannah River and into Georgia (trans-river flow). As part of a 1991–97 study, the U.S. Geological Survey completed a steady state ground-water flow model simulating predevelopment and 1987–92 flow conditions for the Savannah River Site and vicinity. Overall, ground-water withdrawals have increased from 80 million gallons per day for the model simulation period from 1987 through 1992 to 117 million gallons per day in 2000. Ground-water use for irrigation increased from 24.8 million gallons per day in 1995 to 63.3 million gallons per day in 2000. Most of this use was from the Upper Three Runs aquifer in the southern part of the study area and the Gordon aquifer and Dublin aquifer system in updip areas to the north. Potentiometric surface maps show average head declines of 10.6 feet in wells tapping the Upper Three Runs aquifer, 12.5 feet in wells tapping the Gordon aquifer, 8.6 feet in wells tapping the Dublin aquifer system, and 5.5 feet in wells tapping the Midville aquifer system. The water level in wells at the Brighams Landing well-cluster site shows a downward trend in each of the aquifers along with the seasonal decline from groundwater withdrawals for irrigation in the Gordon aquifer. Potentiometric-surface maps constructed from 2002 water levels that show overall declines in aquifer heads have shifted the contours to the west-northwest on the Georgia side and to the north on the South Carolina side of the study area. The ground-water divide beneath the Savannah River has shifted in the upstream direction for the Gordon aquifer and has extended farther downstream for the Dublin and Midville aquifer systems