Slurry wall construction in deep mined area

The Osborne Landfill Superfund site was a 72,850 square meter (18-acre) abandoned strip mining excavation pit located in northwestern Pennsylvania that was used for disposal of waste for more than 20 years until the mid-1970's. The landfill was used for the disposal of approximately 191,000 cubic meters (250,000 cubic yards) of municipal and industrial wastes. The wastes in the landfill became saturated after placement because the waste pit was connected to an extensive flooded deep mine system. In 1984 the site was placed on the National Priority List, primarily as a result of the presence of drums on the surface of the site. Following completion of a remedial investigation and feasibility study, the United States Environmental Protection Agency proposed a remedy for the site that included removal of all materials from the mine pit, backfilling the pit with clean material, and constructing a RCRA landfill above the clean backfill for disposal of the waste. The agency did not believe that an in-place closure/containment option would work for the site because of the deep mine void system in contact with the landfill. The estimated cost of the EPA's alternative was about $26 million. An in-place closure alternative remedy was proposed that included a slurry wall system installed through the mine voids to contain leachate. Studies were :performed to demonstrate that the slurry wall was capable of being successfully installed and maintained by first grouting the mine void system. This unique method of in-place closure - grouting mine voids to facilitate construction of a slurry wall - had never been done on a Superfund site. The alternative remedy was accepted by EPA and will save approximately $15 million in remedial costs.