Ex-situ treatment of dense nonaqueous phase liquids using calcium oxide (quick lime)

Open excavation was selected to remove dense, non-aqueous phase liquids (DNAPLs) identified by previous assessment activities at the FDOT Fairbanks Disposal Pit in Gainesville, Florida. The DNAPLs resulted from the disposal of asphalt testing residue and consisted primarily of trichloroethene and 1,1,1-trichloroethane. Presumptive and visual evidence of DNAPLs had been found in three areas of the site. Excavation of all three areas was conducted and DNAPLs were observed as predicted. The original plan called for ex-situ vacuum extraction of all contaminated soils. All potentially contaminated soils were to be processed through a rotary trommel, staged in 100 cubic yard piles, and sampled for analytical testing. Due to the increasing clay content of the deeper soils, the trommel could not be used for most of the potentially contaminated soils. Quick lime was mixed into the soils at an approximate 5% ratio to improve the soil handling characteristics. The combination of the heating and chemical reaction between the soils and the lime removed the contaminants to below the leachability soil cleanup target levels, and all contaminated soils were ultimately treated by mixing with quick lime. The soils treated with quick lime were returned to the excavation to stabilize the slopes after confirmation soil samples verified the treatment goals had been reached. Approximately 10,000 cubic yards of soil were treated with quick lime, saving several million dollars as compared to off-site disposal.