The Pennsylvania Department of Environmental Protection approved the report Monday detailing what caused the 2017 collapse at Greentree Landfill in Kersey, Elk County.
An investigation at the landfill found the placement of non-conventional waste streams caused the slope failure that killed William Pierce on February 8, 2017.
The DEP required advanced disposal, which owns the landfill, to investigate and submit a root cause report.
In the report, it says things like low shear strength sludges and other operational factors caused the collapse.
Pierce was driving a wheel trash compactor in the area the collapse happened.
Pierce was trapped and killed under 40 feet of debris. It took crews three days to find his body.
The report says Advanced Disposal continues to remediate the area where the slope failed.
The company has also paid $695,000 in penalties.
Penalties were paid to the Solid Waste Abatement Fund, which helps address problems at abandoned landfills and anti-littering and dumping initiatives.