RADON TRACING OF GROUNDWATER INPUT INTO PAR POND, SAVANNA RIVER SITE

The groundwater contribution into Par Pond, a former cooling reservoir for two nuclear reactors located on the Department of Energy's Savann ah River Site (South Carolina), was estimated using a standard hydrolo gic budget as well as one augmented by a natural tracer approach. We d etermined a geochemical budget for Rn-222, normally found at much high er concentrations in groundwater than surface waters, to assist in con straining 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 adv ection-diffusion model. All hydrologic parameters and radon concentrat ions were monitored seasonally from February 1994 to August 1995. Usin g the water balance approach alone, the average groundwater discharge entering the lake was estimated to have an upper limit of approximatel y 0.95 +/- 0.13 m(3) s(-1). The groundwater contribution obtained usin g 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 profile s show enhanced Rn-222 concentrations in some areas indicating that gr oundwater enters Par Pond mostly through a small region in the norther n portion of the lake, probably via small seeps or springs. Estimates show that groundwater plays a significant role in the overall water bu dget of the lake, accounting for 10%-33% of the total estimated inflow from all measured sources. Our results show that supplementing a stan dard hydrological water balance with radon budget considerations helps to constrain estimated groundwater flow into surface reservoirs. (C) 1997 Elsevier Science B.V.