HR: 09:15h
AN: H41I-06    [Abstracts]
TI: Tracing the Origin of Radioactivity in Groundwater from the Negev, Israel
AU: * Vengosh, A
EM: avnerv@bgumail.bgu.ac.il
AF: Ben Gurion University, Department of geological and Environmental Sciences, PO Box 653, Beer Sheva, 84105 Israel
AU: Pery, N
EM: peryn@bgumail.bgu.ac.il
AF: Ben Gurion University, Department of geological and Environmental Sciences, PO Box 653, Beer Sheva, 84105 Israel
AU: Paytan, A
EM: apaytan@pangea.Stanford.EDU
AF: Stanford University Stanford University, Department of Geological and Environmental Sciences, Stanford, CA 94305-2115 United States
AU: Haquin, G
EM: Gustavo@soreq.gov.il
AF: Soreq Nuclear Research Center, Nahal Soreq, Yavne, 81800 Israel
AU: Enhanany, S
EM: sarael10@water.gov.il
AF: Water Commission, 4 Masger Street PO box 20365, Tel Aviv, 61203 Israel
AU: Pankratov, I
EM: irenap60@water.gov.il
AF: Water Monitoring laboratory, Water Commission, Institute of Soil, Water, and Environmental Sciences, Volcany Center PO Box 6, Bet Dagan, 50250 Israel
AB: In normal groundwater conditions natural radionuclides are typically retained on the aquifer matrix and their activity in the groundwater is low. Radium is exceptional since the ratio between adsorbed and dissolved radium depends the ionic strength of the solution. Under high salinity radium is rapidly desorbed and accumulates in the liquid phase. Here we report the results of a geochemical study that investigates the origin of radioactivity in brackish to saline groundwater from the Negev and Arava Valley, Israel. We use the Ra isotope quartet (226Ra-half life 1600 y, 228Ra - 5.6 y, 224Ra - 3.6 d, 223Ra - 11.4 d) to discriminate between radioactivity derived from a thorium source (high 228Ra/226Ra and 224Ra/223Ra ratios) found in groundwater flowing in the Nubian Sandstone aquifer and an uranium source (low 228Ra/226Ra and 224Ra/223Ra ratios) in groundwater flowing in carbonate (Upper Cretaceous) aquifer. We show that the activity of 226Ra in groundwater from the carbonate aquifer is positively correlated with that of the salinity. In the Nubian Sandstone aquifer, however, no such correlation was found. Instead, we observed an inverse correlation between 228Ra activity and sulfate and a positive correlation with barium contents. Given the high H2S content of the ground water, we hypothesized that sulfate reduction process triggers radium leaching to the water, probably due to barite dissolution and anoxic conditions in the aquifer. These findings indicate that high radioactivity can also be found even in low-saline groundwater and that the isotopic ratios of radium are sensitive tracers for the water-rock interactions and thus reconstructing the flow paths in different aquifer matrix (i.e., carbonate versus sandstone).
DE: 1831 Groundwater quality
DE: 1871 Surface water quality
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
DE: 1045 Low-temperature geochemistry
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting