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groundwater modeling for Freeway Landfill

groundwater modeling for Freeway Landfill
Minnesota Pollution Control Agency

modeling predicted groundwater conditions clarifies technically challenging issue

The Freeway Landfill is part of a larger, aging industrial area of Burnsville, Minnesota, that has been eyed for future development. The landfill owner and the Minnesota Pollution Control Agency (MPCA), through its Closed Landfill Program, were evaluating alternatives and developing plans for final closure of the landfill, which was permitted in the early 1970s and predates the introduction of liners beneath waste.

The existing landfill site has relatively shallow bedrock and is located between the Minnesota River and a deep-rock-quarrying operation where significant dewatering has been ongoing for decades and has heavily influenced existing groundwater conditions. Barr was called upon to develop a groundwater model to predict changes in groundwater elevation and flow paths that will eventually occur when quarry operations are discontinued and the deep pit fills with groundwater.

Our groundwater model assessed the anticipated rebound in the water table and its interaction with the unlined waste in the current landfill configuration and estimated potential future contaminant impacts to groundwater, including the potential for contaminant migration toward the river. Essentially, Barr modeled groundwater conditions that do not yet exist and will be vastly different than those that do.

The predicted changes from Barr’s groundwater model were critical in future plans for the landfill and its surrounding properties, including viable closure options, which ranged from establishing a new cap over the old landfill to completely excavating all waste material and placing it in a new, MPCA-compliant, lined landfill. The reconstruction option provides for better control of methane gas generated by the decaying waste at the landfill and creates new opportunities for redevelopment by shifting and consolidating the landfill to a smaller footprint.

The project involved coordination across a diverse group of stakeholders, including the MPCA, US EPA, City of Burnsville, Dakota County, Freeway Landfill owner, quarry owner, development interests, and neighboring property owners. The modeling results helped clarify a technically challenging issue that had been complicating the group’s long-range planning and redevelopment efforts.