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Geochemistry of groundwater in tertiary and cretaceous sediments of the southeastern Coastal Plain in eastern Georgia, South Carolina, and southeastern North Carolina
Author(s) -
Lee Roger W.,
Strickland Donald J.
Publication year - 1988
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/wr024i002p00291
Subject(s) - aquifer , geology , groundwater , groundwater recharge , coastal plain , geochemistry , hydrology (agriculture) , paleontology , geotechnical engineering
Geochemical samples of groundwater taken along hydrologic flow paths in eastern Georgia, South Carolina, and southeastern North Carolina, from noncalcareous sand aquifers, largely of Cretaceous age, are dominated by sodium and bicarbonate ions. Calcareous sand aquifers, largely of Tertiary age, contain water whose chemistry is dominated by calcium and bicarbonate ions, but may evolve downgradient to sodium and bicarbonate dominance. Water chemistry in both types of aquifer evolves to sodium chloride dominance as a result of fresh water mixing with subsurface brines or seawater present in the deeper downgradient parts of the aquifers. Principal aqueous chemical reactions appear to occur in five reaction zones in the aquifers and include feldspar hydrolysis to kaolinite, calcite dissolution, calcium‐for‐sodium cation exchange, and neoformation of sodium smectite in the downgradient parts of the aquifers. Redox reactions produce dissolved iron concentrations greater than 1 mg/L near the recharge areas. Organic matter in the aquifers is oxidized to CO 2 by iron reduction and sulfate reduction processes. Production of CO 2 by a methanogenic process may also occur. Geochemical mass‐transfer models simulating the observed chemistry in western Alabama and eastern Mississippi have been extended to account for higher concentrations of sodium and bicarbonate observed in the South Carolina part of the aquifers.