EVIDENCE FOR GROUNDWATER CIRCULATION IN THE BRINE-FILLED AQUITARD, OAK-RIDGE, TENNESSEE

Various geologic, hydrologic, and geochemical methods were used to ass ess active ground-water circulation in a brine-filled, deep (> 50 m be low land surface) aquitard underlying the Oak Ridge Reservation, Tenne ssee. In places, the brine which was presumed to be stagnant in the pa st, contains various contaminants. If ground-water circulation is viab le in the brine-containing formations, then remediation or containment of the deep-seated contaminants should be considered a high priority. Data used to determine this included (1) spatial and temporal pressur es and hydraulic heads measured in the aquitard, (2) hydraulic paramet ers of the formations in question, (3) vertical temperature gradients, and (4) spatial and temporal chemical and isotopic composition of the saline ground water. Conclusions suggest that the saline water contai ned at depth is not isolated (in terms of recharge and discharge) from the overlying active and fresh-water- (< 500 mg/l) bearing units, Con sequently, influx of young water (and contamination) from land surface does occur. Potential discharge into the shallow aquifers was assumed where the hydraulic head of the saline water was higher than that in the shallow aquifers, accounting for temperature and salinity anomalie s observed close to land surface. The confined water (and dissolved so lutes) move along open conduits at relatively high velocity into adjac ent, more permeable units.