Author(s): Burmshik Kim; Kenneth F. Steele
Linked Author(s):
Keywords: Mississippi embayment; Holocene; Pleistocene; Quaternary; Ground water; Oxidation; Reduction; Metals; Alluvial aquifer; Management
Abstract: The Mississippi River Valley alluvial aquifer in Arkansas is composed of Holocene and Pleistocene (Quaternary) age sediments and is an important source of irrigation and drinking water supplies. Quality of ground water from these two Quaternary sediment deposits was compared to determine the hydrogeochemical characteristics of the two units. Statistical and graphical data show that wells in Holocene sediments have higher Fe, Mn, Ba, F and PO4, whereas wells in Pleistocene sediments have slightly higher HCO3, alkalinity and Br concentrations and higher pH values. These observations are interpreted to be the result of different grain sizes and organic matter content in these two units, which produce different ground-water flow and oxidation-reduction conditions. The reducing environment of Holocene fine-grained sediment is caused by the decomposition of organic matter and by restricted ground-water flow, which produces an anoxic condition with lower pH. These conditions result in mobilization of heavy metal ions and PO4. Well-sorted, larger grain size results in greater permeability of Pleistocene sediment. Greater permeability produces higher ground-water flow and results in more oxidizing conditions. This oxidizing condition preserves hydroxyoxide minerals present in the sediment. If anoxic water containing dissolved heavy metals and PO4 is mixed with the oxic water precipitation of hydroxyoxide and phosphate minerals occurs. The results of this project demonstrate that basic geologic information can be used to predict the quality of ground water from the alluvial aquifer. The predicted water quality can be used to select well sites based on desired water quality and/or be prepared for appropriate water treatment. This type of information on ground-water quality is an important aspect of water resources management.
Year: 2005