HR: 11:05h
AN: H42A-03    [Abstracts]
TI: Mechanisms of Radium Mobilization for Radium-Rich Groundwater from the Nubian Sandstone and Carbonate Aquifers in the Negev, Israel: Implications for Fossil Groundwater Resources in the Middle East
AU: * Vengosh, A
EM: vengosh@duke.edu
AF: Earth & Ocean Sciences, Duke University, EOS, Box 90227, Duke University, Durham, NC 27708, United States
AU: Peri, N
EM: nizpery@gmail.com
AF: Ben Gurion University, Dept. of Geological and Environmental Sciences, Ben-Gurion University of the Negev, P.O. Box 653, Beer Sheva, 84105, Israel
AU: Haquin, G
EM: gustavo@soreq.gov.il
AF: Soreq Insitute, Radioactivity Measurement Section Soreq NRC, Yavne, 81800, Israel
AU: Paytan, A
EM: apaytan@stanford.edu
AF: Stanford University, Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115, United States
AU: Pankratov, I
EM: irenap60@water.gov.il
AF: Israeli Water Commission, Water Monitoring Laboratory, PO Box 6, Bet Dagan, 50250, Israel
AU: Elhanani, S
EM: sarael10@water.gov.il
AF: Israeli Water Commission, Water Monitoring Laboratory, PO Box 6, Bet Dagan, 50250, Israel
AU: Karpas, Z
EM: karpas4@netvision.net.il
AF: Nuclear Research Center, Nuclear Research Center, Negev, P.O. Box 9001, Beer Sheva, 84190, Israel
AB: The radium isotope quartet (226-Ra, 228-Ra, 224-Ra, 223-Ra), radon, and uranium (238-U, 234-U) isotopes were investigated in brackish to saline groundwater from the Nubian sandstone and Lower Cretaceous carbonate aquifers in the Negev, Israel. Our data show that Ra activity in both aquifers are high and far exceeds international drinking water threshold levels. The 228-Ra/226-Ra and 224-Ra/223-Ra ratios in the groundwater from the two aquifers are closely associated with the measured of 232-Th/226-Ra and predicted 224-Ra/223-Ra ratios in the respective aquifers rocks. This indicating that Ra in the Nubian sandstone is derived from interactions with rocks hosting nuclides from both Th- and U-decay series, whereas the carbonate aquifer contributes nuclides exclusively from the U-decay series. In the sandstone aquifer we found that Ra activity is strongly correlated with temperature. The high 224-Ra/228-Ra, d223Ra (defined as 223-Ra/226-Ra/0.046) (>1) and 234-U/238-U (3.3) ratios in the Nubian groundwater suggest that Ra is primarily derived from recoil process on the aquifer solids. We quantified the Ra recoil and retention by normalizing the 224-Ra to 222-Rn activities in the water, taking into account the 232-Th/226-ra ratios in the aquifer rocks. Given that a large fraction of Ra is in the form of RaSO4 species (a range of 0.15 to 0.5) and the correlation of RaSO4 species with Ba content we propose that Ra recoil is retained by co-precipitation onto secondary barite mineral and/or exchange with surface coating. In the carbonate aquifer we show that Ra activity is strongly correlate with both salinity and dissolved oxygen content. Groundwater with high 226-Ra activity has typically low d223Ra ratios and 222-Rn/226-Ra ratios, which suggests that Ra mobilization is controlled by desorption from surface coating that is enhanced under conditions of high salinity and reduced groundwater. Our findings indicate that under stagnant groundwater conditions, Ra can be mobilized from aquifer rocks with common Ra activities, without significant Ra removal (e.g., adsorption). The lack of significant Ra sinks is due to combination of factors including reducing conditions, lack of available adsorption sites, high temperature (that inhibit both barite saturation and adsorption), and groundwater chemistry (e.g., formation of RaSO4 species). These findings could have implications for possible high Ra anomalies in many other similar groundwater basins in the Middle East.
DE: 1040 Radiogenic isotope geochemistry
DE: 1065 Major and trace element geochemistry
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
SC: Hydrology [H]
MN: 2007 Joint Assembly