U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Concentrations of Chlorofluorocarbons and Other Gases in Ground Water at Mirror Lake, New Hampshire

Abstract

The concentrations of chlorofluorocarbons (CFC's) were measured in samples of ground water from 51 different depth intervals in wells completed in the low-permeability glacial till and fractured crystalline rocks at Mirror Lake. The CFC concentrations were used to model water-recharge ages. The ground-water ages generally increased with depth from land surface and were consistent with the reconstructed tritium (³H) concentrations. A 6°C water-recharge temperature was obtained from the nitrogen (N₂) to argon (Ar) ratios from the wells completed in the glacial till. The dissolved N₂, Ar, and helium concentrations generally increased with depth from land surface. Excess air in ground water ranges from about 0 to 19 cubic centimeters per liter in some deep wells. In addition to the excess air, some wells contain significant amounts of excess N₂. Enrichment in the concentrations of sulfate, calcium, and magnesium were present in some ground waters with CFC-recharge ages of 1963 to 1973.