Lantman’s Market Bedrock MTBE Investigation

Since the 1990s, WHEM has been involved in Lantman’s long-term investigation and remediation of the complex bedrock aquifer contamination issue in the Town of Hinesburg, Vermont. The source of contamination is a former gasoline underground storage tank (UST) system at the Lantman’s property, which released petroleum compounds, including Methyl Tert-Butyl Ether (MTBE). MTBE is a persistent groundwater contaminant and it has spread throughout the complex glacial aquifer system. 

MTBE had been detected in a nearby industrial water supply well since at least 1999, which eventually ceased operations in 2008. This caused changes in groundwater elevations and flow direction leading to the migration of MTBE toward former Town of Hinesburg water supply wells, where contamination was first detected in December 2008. Hydrogeologic assessments revealed a strong downward vertical gradient through a fractured clay layer, coupled with a dewatered soil/bedrock interface driven by the pumping of major water supply wells. This unique setting facilitated the movement of contaminants into the bedrock aquifer, requiring a targeted and robust remediation approach.

In response, WHEM designed and oversaw the installation of a dual remediation system at the Lantman’s property in 2008, combining a vapor multi-phase extraction (MPE) and groundwater extraction system (GES) technologies. These systems were effective in removing petroleum mass and interrupting the migration of contaminants toward the municipal supply. Calculations indicate the MPE system removed approximately 99-gallons of hydrocarbons from the subsurface, and the GES mass recovery calculations indicate the removal of approximately 8-gallons of MTBE from the groundwater. During system operation, WHEM routinely monitored the former Town supply wells for benzene and MTBE, with results demonstrating the reduction in contaminant concentrations to satisfy drinking water standards.

WHEM has continued to conduct long-term monitoring and network optimization, including the strategic installation of additional monitoring wells to improve data resolution and understanding of the site’s hydrogeologic behavior. This project highlights WHEM’s expertise in fractured bedrock environments, petroleum remediation, and the protection of critical water supplies in Vermont communities.

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