Trichlorofluoromethane in groundwater—A Possible tracer and indicator of groundwater age

Abstract

Trichlorofluoromethane, an entirely man‐made material, has become a detectable component of the atmosphere. Because of its unique atmospheric history, the presence of CCl3F in groundwater is potentially significant in terms of groundwater age. The age relationship stems from the fact that precipitation, exposed to CCl3F in the atmosphere, will pick up an amount that is proportional to the atmospheric CCl3F concentration. If a portion of this water infiltrates into the subsurface to become groundwater, it can be differentiated from older groundwater (that infiltrated prior to the buildup of CCl3F in the atmosphere) on the basis of its CCl3F content. In order to evaluate the temporal significance of CCl3F in groundwater, preliminary investigations were conducted in three areas where the hydrology was well understood and where tritium measurements had been made in the past. They were: the Wharton tract of southern New Jersey; Hot Springs National Park in Hot Springs, Arkansas; and the Edwards aquifer of south central Texas. Good agreement was observed between the CCl3F data and the hydrologic controls. The Texas study also revealed a series of anomalous CCl3F concentrations (up to 35 × 10−9g CCl3F/I H2O) that were too high to be of atmospheric origin. The anomalous points occurred in a line extending from the northwest corner of San Antonio for a distance of 74 km northeast along the Balcones fault zone and are interpreted as representing the migration of CCl3F from a point source, thus indicating the potential of this and similar compounds as hydrologic tracers.