Thermal Conduction Heating for a 125 ft Deep TCE Source—Multiple Lines of Evidence for Verification of Remedial Goals

Abstract

AbstractThis paper describes thermal conduction heating of a trichloroethylene (TCE) source zone within vadose zone soils consisting of glacial till at depths of 50 to 125 ft below an active manufacturing facility. The performance objectives and metrics used to determine remediation success are presented. Access limitations inside the facility prevented traditional spatial soil confirmation sampling, which made performance assessment a unique challenge. Instead, the project team developed an approach utilizing multiple lines of evidence to document remedy completeness. These lines of evidence included achievement of target temperatures within the treatment volume, demonstration of asymptotic vapor concentrations extracted from the treatment volume, achieving modeled energy input goals, and verifying TCE concentrations in post‐treatment soil samples collected at the few accessible locations within the operational facility. The treatment volume was divided into three discrete treatment areas or heating groups, each constructed and heated independently in order to meet an aggressive project schedule. Additionally, each line of evidence was required to be met in each group. After approximately 283 days of heating, temperatures exceeded 90 °C at 95% of the temperature monitoring points, TCE levels had diminished to asymptotic levels in the recovered vapors, and mass removal rates from the treatment volume declined to minimal levels. Confirmatory soil sample results indicated that average TCE concentrations achieved were more than an order of magnitude below the remedial goal of 1 mg/kg.