Formatted Title
Unexpected Construction Dewatering Event Causes Changes in Groundwater Plume Flow Direction and Failure of the Groundwater Extraction System
Background/Objectives
An unexpected construction dewatering event changed the flow of groundwater at a closed landfill site in central Wisconsin causing the horizontal groundwater extraction system to fail. Additionally, a dilute plume of chlorinated compounds in groundwater changed flow direction from previous trends. This plume had been previously identified and had been contained by the horizontal groundwater extraction system since the late 1990s. However, the drawdown event caused detections in new wells and sparked a supplemental site investigation.
Approach/Activities
When the landfill staff first noticed a drop in the water levels in the horizontal extraction system, water levels were measured in the monitoring well network and a 3-D visualization was developed. The model showed shallow groundwater flowing towards the northwest corner of the site, a distinct change from ambient conditions. Visualizations of the vinyl chloride plume showed movement of the plume off the western property boundary and identified a source area. This analysis informed options to redesign the groundwater treatment/containment system at the site.
Results/Lessons Learned
The Wisconsin Department of Natural Resources has now added the landfill to its registry of contaminated sites, which should make it easier to determine that a plume is nearby when planning construction events. The drawdown event served as a pivot point to reassess the current remediation strategy and redesign the remedy to fit the current needs of the site, decades after the groundwater extraction system was built.