Radon tracing of groundwater input into Par Pond, Savannah River Site

The groundwater contribution into Par Pond, a former cooling reservoir for two nuclear reactors located on the Department of Energy's Savannah River Site (South Carolina), was estimated using a standard hydrologic budget as well as one augmented by a natural tracer approach. We determined a geochemical budget for Rn-222, normally found at much higher concentrations in groundwater than surface waters, to assist in constraining the hydrologic estimates. The radon budget accounted for all quantifiable surface sources and sinks including the flux across the sediment-water interface which was determined by application of an advection-diffusion model. All hydrologic parameters and radon concentrations were monitored seasonally from February 1994 to August 1995. Using the water balance approach alone, the average groundwater discharge entering the lake was estimated to have an upper limit of approximately 0.95 +/- 0.13 m(3) s(-1). The groundwater contribution obtained using the combined hydrologic/Rn-222 approach ranged from 0.17 to 0.76 m(3) s(-1) with a best estimate of 0.35 +/- 0.16 m(3) s(-1). Lake profiles show enhanced Rn-222 concentrations in some areas indicating that groundwater enters Par Pond mostly through a small region in the northern portion of the lake, probably via small seeps or springs. Estimates show that groundwater plays a significant role in the overall water budget of the lake, accounting for 10%-33% of the total estimated inflow from all measured sources. Our results show that supplementing a standard hydrological water balance with radon budget considerations helps to constrain estimated groundwater flow into surface reservoirs. (C) 1997 Elsevier Science B.V.