ELSEVIER Journal of Hydrology 203 (1997) 209-227 Radon tracing of groundwater input into Par Savannah River Site Journal tg Y Pond, D. Reide Corbett”**, William C. Burnetta, Peter H. Cablea, Sue B. Clarkb3 ’ “Environmental Radioactivity Measurement Facility, Department of Oceanography, Florida State Univer.~ity Tallahassee, Florida 32306-3048, USA hSavannah River Ecology Luboratov, University of Georgia. Aiken, South Carolina 29802. USA Received 6 August 1996; received in revised form 28 August 1997: accepted 28 August 1997 Abstract 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, normally found at much higher concentrations in groundwater than surface waters, to assist in constraining the hydrologic estimates. The radon budget accounted for ail 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 m3 s-‘. The groundwater contribution obtained using the combined hydrologic/***Rn approach ranged from 0.17 to 0.76 m3 s-’ with a best estimate of 0.35 ? 0.16 m3 s-‘. Lake profiles show enhanced “*Rn 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 IO%-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. 0 1997 Elsevier Science B.V. Keywords: Ground water discharge; Water balance; Radon; Seepage: Tracers 1. Introduction I. 1. Background The interaction of groundwater with surface water in lakes and other standing bodies of water received *Tel.: 904 644 6703; Fax.: 904 644 2581; e-mail: corhett@ ocean.fsu.edu ’ Current address: Department of Chemistry, Washington State University, Pullman, Wa. 99164, U.S.A. increased attention recently because of its potential significance as a source of nutrients and/or contami- nants. Groundwater could be a significant contributor to the overall water and chemical budgets of any reservoir where hydraulic gradients are directed toward that body of water. An understanding of such inter- actions is necessary, therefore, to protect and control the quality of surface waters. Quantitative information about how groundwater enters lakes and other bodies of water via springs 0022-1694/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved PII SOO22- 1694(97)00103-O