Development of a solute transport model to characterize the movement of sodium chloride through glacial sediments at Fermi National Accelerator Laboratory in Batavia, Illinois

The Central Utilities Building (CUB) Pipe and Clay Tile Field (study area) within Fermi National Accelerator Laboratory (Fermilab) is a leach field system designed to dispose effluent containing high levels of chloride generated by the CUB resin regeneration system. The purpose of this study is to develop a two-dimensional numerical transport model to simulate the extent and rate of vertical migration through the glacial units to Class I groundwater (boundary between the glacial deposits and the bedrock).; The developed code is based on Random-Walk theory described by Prickett (1981). Verification involved comparing model simulations under the same boundary conditions to Hunt's (1978) two-dimensional analytical solutions resulting in a close match. The model, calibrated to field observations from 1989 to 2004, suggests a longitudinal dispersivity of 24.4 m and transverse dispersivity of 2.44 m. An extensive sensitivity analysis indicates that the model is more sensitive to changes in velocity and specific discharge than dispersivity. Modeling determines the initial concentration of the source to be 11565 mg/l. The prediction model suggests that the concentration of chloride at the Class I groundwater reaches 215--240 mg/l in 150 years. These levels should not significantly impact the water quality in the bedrock, as hydrodynamic dispersion will cause further dilution in chloride concentration as the plume moves through the bedrock.