Arsenic in glacial aquifers: Sources and geochemical controls

Walton R Kelly, Thomas R. Holm, Steven D Wilson, George S Roadcap

Research output: Contribution to journalArticle


A total of 176 wells in sand-and-gravel glacial aquifers in central Illinois were sampled for arsenic (As) and other chemical parameters. The results were combined with archived and published data from several hundred well samples to determine potential sources of As and the potential geochemical controls on its solubility and mobility. There was considerable spatial variability in the As concentrations. High concentrations were confined to areas smaller than 1 km in diameter. Arsenic and well depth were uncorrelated. Arsenic solubility appeared to be controlled by oxidation-reduction (redox) conditions, especially the presence of organic matter. Geochemical conditions in the aquifers are typically reducing, but only in the most reducing water does As accumulate in solution. In wells in which total organic carbon (TOC) was below 2 mg/L and sulfate (SO42-) was present, As concentrations were low or below the detection limit (0.5 μg/L). Arsenic concentrations >10 μg/L were almost always found in wells where TOC was >2 mg/L and SO42- was absent or at low concentrations, indicating post-SO42- reducing conditions. Iron (Fe) is common in the aquifer sediments, and Fe oxide reduction appears to be occurring throughout the aquifers. Arsenic is likely released from the solid phase as Fe oxide is reduced.

Original languageEnglish (US)
Pages (from-to)500-510
Number of pages11
JournalGround Water
Issue number4
StatePublished - Jul 1 2005

ASJC Scopus subject areas

  • Water Science and Technology
  • Computers in Earth Sciences

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