GROUNDWATER CHEMISTRY OF FLOODPLAIN SEDIMENTS NEAR THE LITTLE TALLAPOOSA RIVER, GEORGIA, USA

Groundwater hydrochemical monitoring of alluvium beneath a portion of the Little Tallapoosa River floodplain in the Georgia Piedmont, Carroll County, Georgia, reveals complex spatial distribution of groundwater composition and relatively little temporal variation. We sampled groundwater from 15 piezometers installed in organic-rich, predominantly fine-grained floodplain alluvium at depths between 1.0 and 4.9 m. Samples were collected five times over an eight-month period under conditions including drought and flood. Most waters are of a mixed-cation bicarbonate type; sodium chloride waters are also present. Approximate TDS ranges from 30 to 270 mg/L; pH ranges from 4.5 to 6.1. Concentrations of some redox sensitive species (O₂, NO₃^-, Fe²⁺, Mn²⁺) vary considerably within the dataset. Preliminary colorimetric analysis suggests As concentrations in some wells greater than 30 mg/L; As concentrations are greatest in wells with low apparent pe. Results show that hydrochemistry of this floodplain environment is heterogeneous over very small areas. At least some of the heterogeneity is explained by variable redox chemistry; other important processes may include mineral dissolution and ion exchange. There does not appear to be significant exchange with local surface waters.