Geologic control of stream water composition in Cherokee, Smith and Rusk Counties, Texas

Water samples from selected streams in east Texas were analyzed to determine the relationship of specific geologic formations and their influence on stream water quality. The two lower formations of the Claiborne Group, the Carrizo Sandstone and the Reklaw Formation, have a subtle influence on the chemical composition and water quality associated with local streams.; As these streams travel across the Reklaw Formation, natural buffers in the form of clays, alluvial sediments and organics tend to lessen the impact of the Reklaw's acid sulfate weathering patterns. Acidity of these waters increase as they flow over the contact between the Reklaw Formation and the Carrizo Sandstone. The lack of buffers in the Carrizo Sandstone allows pH values to drop and sulfate concentration to increase slightly.; Thirty-six samples from six streams were analyzed semi-monthly over a period of eight months to document how their chemical composition and concentration levels changed as they flowed across these formations. While most of the 36 sample locations yielded results within normal limits, several locations produced anomalous readings. As these streams continue through the study area and merge with larger rivers, attenuation and dilution allows pH values to stabilize.