CONTAMINATED GROUNDWATER FLOW CONTROL ACROSS AN INVERTED GROUNDWATER DIVIDE WITH THREE GROUNDWATER CONTROL SYSTEMS

Legacy landfills have impacted water resources across the United States. This presentation evaluates the effectiveness of a multi-component ground water control system (pumping well, pumping trench, and slurry wall) in preventing ground water flow from an unlined solid waste landfill off site. Interactions among multiple groundwater control systems have been primarily evaluated through simulation experiments, and field studies are rare. Here, the groundwater control system was installed near an active unlined landfill to control flux of impacted groundwater. This system of control devices was evaluated using monthly water quality data from a spring on the other side of the groundwater divide. The water chemistry seems to indicate that the impacted groundwater flows primarily through the fractured rock in the ridge (contrary to expectations). This dominant flowpath increases the importance of the collection trench in flow control. In contrast, the groundwater pumping well, designed to capture impacted groundwater flow through local coal seams and sandstones, is less effective, likely due to lower hydraulic conductivity in coal aquifers than expected. Although the groundwater control system reduces the amount of impacted groundwater flow off site, these controls must operate until the landfill is closed and a permanent control (i.e. a clay cap over the landfill) can be installed. While the system did not completely prevent impacted groundwater from flowing off site, when all components are operating, it reduces flux of impacted groundwater. However, when part of the system was not operational, function was substantially diminished. Ultimately, field measurement of system effectiveness reveals that while models can guide design, heterogeneity and unconformities remain a challenge to reliably identify.