Environmental assessment and remediation at an industrial solid waste landfill

Potlatch's Cloquet mill owns and operates a 40 acre industrial solid waste landfill adjacent to the St. Louis River, the largest tributary to Lake Superior. As part of a $500 million pulp mill modernization and expansion project, an expansion permit for the landfill was obtained in 1992. A special condition of the expansion permit was to complete a remedial investigation and feasibility study to assess potential impacts from the landfill on human health and the environment. Initial investigations, which focused on groundwater quality and waste delineation, specifically for dioxins and furans and heavy metals, used an innovative sampling technique developed to collect representative unfiltered groundwater samples. When site investigation revealed historic placement of wastes outside the perimeter of the landfill along the slopes of the river, the focus moved to determining the extent and characterization of the materials. In addition, concern over seeps at the toe of the slope increased when waste was discovered on the slopes. Remedial actions to address waste erosion and seeps included a combination of the following actions: waste removal and slope regrading, placement of horizontal seep collector drains, reinforcement of the slope toe with riprap and returning the site to a natural state using 24 inches of cover soils secured with a long lasting and durable erosion control material and reestablishment of native grasses and woody vegetation. Despite the structured permit approach and the physically complex site, the entire process through remedial actions was completed in four years, two years ahead of the schedule outlined in the 1992 Landfill Permit. This was achieved by making a strong commitment to the remedial actions and fostering a team approach with close coordination among all parties including: the Company, the design consultant, the contractors, the regulatory agencies, and the community.