Isotopic studies in the natural sources of radium in groundwater in Illinois

Gilekson, Robert H.; Perry, Eugene C., Jr.; Cowart, James B.; Holtzman, Richard B.

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https://hdl.handle.net/2142/91635 Copy

Description

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

Issue Date

1984-04-01

Keyword(s)

• Groundwater
• Aquifers
• Water resource development
• Water resource development--Illinois
• Aquifer properties
• Chemical properties
• Evaporite minerals
• Glacial events
• Radium
• Stable isotopes
• Sulfate
• Uranium

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.

Publisher

University of Illinois at Urbana-Champaign. Water Resources Center

Type of Resource

text

Language

English

Permalink

http://hdl.handle.net/2142/91635

Sponsor(s)/Grant Number(s)

• U.S. Department of the Interior
• U.S. Geological Survey

Copyright and License Information

Copyright 1984 held by the authors

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