Relationships between radium and radon occurrence and hydrochemistry in fresh groundwater from fractured crystalline rocks, North Carolina (USA)
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2009-03-30
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Naturally-occurring radionuclides (uranium, radium, and radon), major dissolved constituents, and trace elements were investigated in fresh groundwater in 117 wells in fractured crystalline rocks from the Piedmont region (North Carolina, USA). Chemical variations show a general transition between two water types: (1) slightly acidic (pH 5.0-6.0), oxic, low-total dissolved solids (TDS) waters, and (2) near neutral, oxic to anoxic, higher-TDS waters. The uranium, radium, and radon levels in groundwater associated with granite (Rolesville Granite) are systematically higher than other rock types (gneiss, metasedimentary, and metavolcanic rocks). Water chemistry plays a secondary role on radium and radon distributions as the 222Rn/226Ra activity ratio is correlated with redox-sensitive solutes such as dissolved oxygen and Mn concentrations, as well as overall dissolved solids content including major divalent cations and Ba. Since 224Ra/228Ra activity ratios in groundwater are close to 1, we suggest that mobilization of Ra and Rn is controlled by alpha recoil processes from parent nuclides on fracture surfaces, ruling out Ra sources from mineral dissolution or significant long-distance Ra transport. Alpha recoil is balanced by Ra adsorption that is influenced by redox conditions and/or ion concentrations, resulting in an approximately one order of magnitude decrease (~ 20,000 to ~ 2000) in the apparent Ra distribution coefficient between oxygen-saturated and anoxic conditions and also across the range of dissolved ion concentrations (up to ~ 7 mM). Thus, the U and Th content of rocks is the primary control on observed Ra and Rn activities in groundwater in fractured crystalline rocks, and in addition, linked dissolved solids concentrations and redox conditions impart a secondary control. © 2008 Elsevier B.V. All rights reserved.
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Vinson, DS, A Vengosh, D Hirschfeld and GS Dwyer (2009). Relationships between radium and radon occurrence and hydrochemistry in fresh groundwater from fractured crystalline rocks, North Carolina (USA). Chemical Geology, 260(3-4). pp. 159–171. 10.1016/j.chemgeo.2008.10.022 Retrieved from https://hdl.handle.net/10161/6927.
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Avner Vengosh
Avner Vengosh is a Distinguished Professor and Nicholas Chair of Environmental Quality at the Nicholas School of the Environment. He is the chair of the Division of Earth and Climate Sciences. Professor Vengosh and his team have studied the energy-water nexus, conducting pioneer research on the impact of hydraulic fracturing and coal ash disposal on the quantity and quality of water resources in the U.S. and China. He has also investigated the sources and mechanisms of water contamination in numerous countries across the globe, including salinity and radioactivity in the Middle East, uranium in India, fluoride in Eastern Africa, arsenic in Vietnam, and hexavalent chromium in North Carolina and China. As part of these studies, his team has developed novel geochemical and isotopic tracers that are used as fingerprints to delineate the sources of water contamination and evaluate potential risks for human health. Currently, his team is engaged in studying phosphate rocks geochemistry and the impact of fertilizers on soil and water quality, unconventional sources of critical raw materials, and potential environmental effects of lithium mining from hard rocks and brines. He is a Fellow of the Geological Society of America (GSA) and International Association of Geochemistry (IAGC). In 2019, 2020 and 2021 he was recognized as one of the Web of Science Highly Cited Researchers. He serves as an Editor of GeoHealth and on the editorial board of the journal Environmental Science and Technology. He has published 171 scientific papers in leading international journals. His recent cross-disciplinary book “Water Quality Impacts of the Energy-Water Nexus” (Cambridge University Press, 2020) provides an integrated assessment of the different scientific and policy tools around the energy-water nexus. It focuses on how water use, and wastewater and waste solids produced from fossil fuel energy production affect water quality and quantity. Summarizing cutting edge research, the book describes the scientific methods for detecting contamination sources in the context of policy and regulations.
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