EPA Region 9

In Situ Thermal Remediation was used to successfully treat benzene, TPH-d, TPH-mo, BaP, and Naphthalene from a former gas plant in EPA Region 9.

Gas Thermal Remediation (GTR™), using Thermal Conductive Heating (TCH), raised the temperature of the soils in the treatment zone of the former MGP site to an average temperature of approximately 325°C.

Pilot Study Remediation

The COC(s) identified at the site include total petroleum hydrocarbons in the diesel (TPH-d) and motor oil (TPH-mo) range, as well as benzene, xylene, naphthalene, benzo(a)pyrene (BaP) and contaminant qualified as BaP equivalents detected in the soils. The maximum detected soil concentration was 54.7 mg/kg (BaP equivalent value), as measured at sample TCH-1-1. The maximum TPH-d concentration was 1,600 mg/kg and the maximum TPH-mo concentration was 2,700 mg/kg. The highest VOC concentrations were observed in the TCH-1 and TCH-14 borings.

The treatment volume was defined for the pilot study as all soil in the vadose zone from 0 to 15 feet bgs in the area surrounding RI Boring B6-6. To ensure that all soils were effectively heated in the treatment volume, wells were placed 5 feet deeper than the bottom of the treatment volume, resulting in a heated volume larger than the treatment volume.

A total of 7 GTR™ heaters and 14 TCH locations were utilized for the pilot study (one GTR™ heater used to heat two TCH wells, the second TCH well applying reheat combustion air from the first TCH with GTR™ heater are called "reheat" wells). The well layout design was optimized after the start up of the project on October 4th. In December, four additional GTR™ heaters were added to supplement heating in certain areas.

The pilot test project of 14 heating wells at EPA Region 9 was successful. The remediation goal of decreasing the Benzo(a)pyrene equivalent contaminants to the target level of less than 0.9 mg/kg was observed in all samples analyzed at the completion of the project.