AMEREN Illinois

O6 ENV completed sub-surface structure removals of the former manufactured gas plant including building foundations, piping, and process structures. The structures were demolished by excavators, the foundation was removed, and debris was sized and segregated. Concrete and metal debris was recycled, and general debris was disposed of at an approved landfill. Additionally, 90,000 tons of impacted soil were excavated and disposed of. O6 ENV discovered that the source of the contamination originated from gas holder tanks that were on-site.

Prior to remedial activities, O6 ENV and its subcontractors installed an engineered earth retention system consisting of a driven steel sheet pile and drilled tangent pile to allow for remedial extents adjacent to open public ROWs. Three levels of tiebacks were installed to achieve final excavated depths of greater than 35 feet below ground surface.

The impacted soil was excavated with an 80,000 lb. hydraulic excavator and loaded into end dump trailers and transported to Republic Envotech Landfill for disposal at the Sub-Title D landfill. The impacted soil was manifested as non-RCRA regulated waste under 40 CFR Section 262.34(a) which provides an RCRA exemption for certain wastes generated from former manufactured gas plant activities. Additionally, 700,000 gallons of MGP-impacted groundwater were treated via an onsite wastewater treatment plant operated by the O6 ENV Class K operator and shipped offsite via tanker to an approved discharge facility.

The excavations were backfilled using soil and gravel from an off-site borrow source. The borrow material was transported by tandem truck, placed with an excavator, and compacted to the recommended levels.