Ground-water geochemistry and its relationship to the flow system at an unmined site in the Eastern Kentucky Coal Field

A comprehensive hydrogeologic and hydrogeochemical study was conducted at an unmined site in the Eastern Kentucky Coal Field. Sixteen piezometers were installed to approximate a vertical grid in a ridge that is characteristic of the geologic and hydrologic conditions of the region. Piezometer placement was based on data collected from geologic core description, geophysical logs, water-injection packer tests, and downhole camera investigations. Water levels were measured on approximately 10-day intervals. Water samples were collected monthly to evaluate temporal variation in water chemistry. A one-time sampling for tritium analysis was performed to aid in the determination of recharge and discharge areas.; Piezometers monitoring shallow, fractured bedrock and coal beds showed the greatest temporal water-level fluctuation and hydrochemical variation. These effects decreased with depth below the surface. Coal beds of the Hazard series probably act to dewater the upper portion of the ridge by laterally transmitting water that discharges as springs or seeps. Interpretation of the tritium data indicates that a significant amount of recharge enters the ridge along the hillslope where fractures, along with a break in the degree of slope, allow for the greatest filtration of ground water.; Temporal variation in ground-water chemistry was minimal at the site except for a few specific cases. Ground water derived from coal seams contained the lowest pH and was predominantly a Ca-Mg-HCO{dollar}sb3{dollar} water type. Water derived from fractured zones varied between Ca-HCO{dollar}sb3{dollar} and Mg-SO{dollar}sb4{dollar} water types. Ground water from the ridge interior is a Na-HCO{dollar}sb3{dollar} type, which contained a high pH and characteristically high F{dollar}sp-{dollar}. Barium was found in a significant concentrations in piezometers near the discharge area (valley bottom) where Na-Cl water types were encountered, although ground water with elevated barium concentrations was shown to exist in other locations. Sulfate reduction and cation exchange appear to control the occurrence of barium.; Reaction path modeling of the geochemical evolution of ground water at the site showed excellent agreement with observed trends. A conceptual model is presented that shows the location of hydrochemical facies zones within the ridge and outlines a set of plausible water-rock reactions for their occurrence.