Pinnacle Engineering was retained by a Minnesota city to assist in securing an Investigation grant and Environmental Cleanup grant from the Minnesota Department of Employment and Economic Development (DEED) for a five-acre property that had previously been used by the City as a municipal dump and was planned to become the anchor development in a new 22-acre industrial park. The Environmental Cleanup grant addressed excavating portions of the dump, hauling excavated material to a permitted landfill, and capping the remaining waste.
Under the Minnesota Pollution Control Agency (MPCA) Voluntary Investigation and Cleanup (VIC) Program, Pinnacle completed a Development Response Action Plan (DRAP), which addressed the cleanup of the dump during site development activities. The DRAP was based on previous assessment work performed by others; however, Pinnacle installed and sampled additional groundwater monitoring wells to more fully characterize the groundwater conditions, pre-cap and post cap. Pinnacle also excavated test pits within the landfill to characterize landfill materials prior to cap placement. Pinnacle designed and constructed the landfill cap in accordance with the DRAP. Following installation of the cap, Pinnacle installed soil vapor wells and monitored the capped landfill for potentially harmful gasses.
The MPCA had previously investigated the dump under the auspices of the Minnesota Closed Landfill Program due to concerns that the dump could be impacting an adjacent river. Before the cap was installed, landfill material was observed floating downstream during spring flooding events and eroding out of the toe of the landfill on the river floodplain. Prior to grading and installing the landfill cap, the toe area was cleaned and re-sloped, impacting over 4,000 square feet of floodplain wetland; Pinnacle obtained wetland permits for work conducted on the floodplain. The modified slope was capped with two feet of clay, a sand layer for drainage, and topsoil. The topsoil was seeded, and erosion control was established to allow vegetation to establish itself. Riprap was placed along the base of the slope to protect it from erosion by river flooding.