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Variations in Shallow Groundwater Composition in Hinds and Madison Counties, Mississippi

Abstract

Groundwater samples collected from municipal water wells from 1970 to 2000 show significant changes in inorganic geochemical compositions in Hinds and Madison counties in central Mississippi. In Hinds County, total dissolved solids (TDS), chlorine, sodium, and sulfate concentrations of the groundwater do not show well-defined depth-related grouping or trends. But, groundwater compositions reveal east-to-west variations. Groundwater with low TDS, chlorine, sodium, and sulfate is found in the eastern part of county. But concentrations of all elements systematically increase westward such that groundwater on the western edge of the county has TDS as high as 900 mg/L. The east-to-west increase in groundwater composition in Hinds County may be related to recharging of aquifers by freshwater from the Pearl River on a structural high caused by the Jackson Dome on the eastern side of the county and its mixing with saline water on the western side of the county.

Two distinct groups of groundwater have been found in Madison County. Group one waters have high TDS, chlorine, sodium, and sulfate values and occur at shallow depths (<250 m). They are restricted to the southeastern part of the county. Group two waters have lower TDS, chlorine, sodium, and sulfate values than group one waters, occur at depths of 250 m to 500 m, and are distributed throughout the county. The cause of this distinct variation in groundwater composition is not clear. It is possible that group one waters are influenced by the upward moving of deep brine along faults.