Mass Transport Modeling in Contaminated Buried‐Valley Aquifer

The U.S. Geological Survey's two‐dimensional solute‐transport and dispersion model (the method of characteristics, or MOC, model) accurately reproduces the chloride‐concentration distribution observed in a buried‐valley aquifer contaminated by a solid‐waste landfill in Butler County, Ohio. The predictive capacity of the calibrated model has utility in water resources planning in regions of ground‐water discharge downgradient of the landfill. Calibration of the ground‐water‐flow model to an observed steady‐state head field indicates a ratio of hydraulic conductivity to diffuse recharge of $8.8\times {10}^{-4}\text{.}$ Mass transport calibration was achieved with a longitudinal dispersivity of 53 m, a transverse dispersivity of 5.3 m, and a chloride concentration of 320 ppm at injection wells used in simulating the contaminant source. The model was calibrated to a contaminant distribution observed 16.7 years after initial landfill operations; 10 and 50 year contaminant‐distribution predictions indicate that the plume will reach a steady‐state equilibrium with the ambient ground‐water flow system after 10 years. The attainment of such a condition could significantly decrease the possibility of future contamination of downgradient domestic supply wells.