Manufactured gas plant remediation beneath a building: underpinning as an alternative to demolition

Remedial investigations at a former manufactured gas plant site indicated the presence of coal tar impacts beneath a church in Newtown, Pennsylvania, USA. Due to the historic nature of the building, alternatives to conventional demolition were considered for removal of the impacts. An engineering/economic analysis concluded that underpinning the building was a cost-effective alternative and would reduce the volume of debris requiring landfill disposal. Twenty-two reinforced concrete columns were installed beneath interior and exterior load-bearing walls. During April and May 2005,1528 tons of soil, the former gas holder and other structures were removed to a depth of 12 feet. These materials were removed with a mini-excavator and transported off-site for treatment and disposal. The excavation was backfilled with cellular concrete and a vapor barrier was installed beneath the portion of the building supported during remediation. The project was completed ahead of schedule, under budget and with no settling or damage to the building.