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Title:Isotopic studies in the natural sources of radium in groundwater in Illinois
Author(s):Gilekson, Robert H.; Perry, Eugene C., Jr.; Cowart, James B.; Holtzman, Richard B.
Contributor(s):Illinois State Geological Survey; Northern Illinois University; Florida State University; Argonne National Laboratory; Grundl, Tim; Socki, Rick; Ahmad, Neaz
Water resource development
Water resource development--Illinois
Aquifer properties
Chemical properties
Evaporite minerals
Glacial events
Stable isotopes
Abstract:Stable and radioactive isotopes in groundwater were studied in an investigation of the natural geologic sources of high concentrations of ²²⁶Ra and ²²⁸Ra in confined aquifers in the Cambrian and Ordovician bedrock of northern Illinois. The covariation of 𝛿¹⁸0 and 𝛿D determined that the groundwater has a meteoric isotopic composition. Groundwater in unconfined aquifers has 𝛿¹⁸0 values (-6.6 to -7.9⁰/₀₀) that are similar to contemporary meteoric water. However, a source of recharge related to glaciation is required for groundwater in confined aquifers of the Cambrian and Ordovician that is significantly depleted in ¹⁸0 (𝛿¹⁸0 values range to -12.7⁰/₀₀ and are less than -9⁰/₀₀ over large regions) . The covariation of 𝛿³⁴S and 𝛿¹⁸0 in dissolved sulfates determined a mixing line between two sources; oxidation of sulfide minerals and dissolution of marine evaporites. Dissolved sulfates from evaporite sources are present in large concentrations in confined aquifers but are of a different isotopic composition than evaporites of Cambrian or Ordovician age. Glaciation may be important with regard to recharge of the sulfates. The ²³⁴U/²³⁸U activity ratio in groundwater from the Cambrian and Ordovician are unexpectedly high; values range from 2.1 to 40.7. The lowest ratios occur in primary recharge zones. In confined aquifers values are greater than 20 over large regions. Alpha recoil damage is a mechanism that contributes to the disequilibrium. However, the regional variation in activity ratios and in ²³⁴U concentrations supports the concept that glacial recharge has contributed to the high ratios. Radiological and geochemical mechanisms that partition ²³⁸U, ²³⁴U and ²³⁰Th on the sandstone matrix are important to the dissolved ²²⁶Ra concentration.
Issue Date:1984-04-01
Publisher:University of Illinois at Urbana-Champaign. Water Resources Center
Genre:Report (Grant or Annual)
Sponsor:U.S. Department of the Interior
U.S. Geological Survey
Rights Information:Copyright 1984 held by the authors
Date Available in IDEALS:2016-09-28

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