Date of Award
Master of Science
The Henry Aquifer in Gallatin County Illinois provides groundwater for municipal, irrigation, industrial, and household wells. The greatest annual withdrawal is by a water utility that serves over 40,000 persons in southeast Illinois. Buried coal refuse at a mine near the water utility has contaminated the groundwater. Remediation efforts, including source control wells on the border of the mine site and low permeability caps over refuse areas attempt to control the migration of contaminants offsite. Current mine land owners believe source control well pumping over 20 years has reduced contamination in the aquifer enough to stop pumping. However, some monitoring wells off the mine site have recently sampled high concentrations of contaminants. Previous studies failed to account for the elevated concentrations found offsite. The purpose of this research is to reevaluate contaminant transport in this region. Specific objectives include a new conceptual model of the hydrostratigraphy and hydrology, revised contaminant source locations and loading, and new groundwater models accurately calibrated to a comprehensive set of monitoring well data. The research included extensive review of prior studies and historical records from the past 50 years. Relevant information was combined in Quantum Geographic Information System (GIS) software for the conceptual and numerical models. A new groundwater modeling pre/post processor for MODFLOW and MT3DMS was ii created for Quantum GIS to calibrate the models and simulate future conditions for risk assessment. Observed hydraulic head and sulfate concentrations from 1984-2015 were used for calibration. In addition, modeled baseflow was compared with observed streamflow in 2017. The calibrated models were used for twelve unique scenarios that forecast contamination from 2017- 2068. The scenarios tested model sensitivity to changes in groundwater management and environmental conditions. The results show that groundwater quality about 300 meters west of the mine deteriorates in all scenarios, water utility wells near the mine are at risk in most scenarios, and that the location and discharge of wells have a commanding effect on the regional groundwater flow and transport systems. This research offers important questions for further study, valuable tools for groundwater management in the region, and shows that without active source control wells, negative impacts to water quality near the mine will likely occur.
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