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Landslide at Ontario County Landfill: DEC investigating after 3.5 acres of cap slides down southwest face

  • / Updated:
  • Staff Report 

A major incident at the Ontario County landfill operated by Casella Waste Management of Ontario LLC (Casella) is under investigation following a landslide late Wednesday.


Approximately 3.5 acres of a new seven-acre permanent cap slid down the southwest face of the landfill. No injuries were reported, and the displaced material remains within the landfill’s boundaries, avoiding any immediate external environmental impact.

Casella, under an Operations Management and Lease Agreement with Ontario County, has been working on this capping project over the summer. The work, executed by third-party contractors and engineers, complied with plans and regulations approved by the New York State Department of Environmental Conservation (NYSDEC). Currently, the cause of the cap failure remains unknown. Ontario County officials, along with Casella and NYSDEC, are conducting extensive independent tests to understand the failure and plan remedial actions.

The incident caused significant movement of soil, damaging some landfill gas collection infrastructure. This has raised concerns about potential increased landfill gas odors in surrounding areas. Despite the damage, it appears that the synthetic waste barrier remains intact, with no waste material exposed or compromised. The affected landfill section was not active in waste acceptance, thus not affecting ongoing operations. Teams from Ontario County, Casella, NYSDEC, and the contractors are focused on determining the failure’s cause and devising a comprehensive and safe remediation plan.