State of the Practice Worldwide: Complex Installation for In Situ Thermal Remediation Beneath an Active Manufacturing Facility

Abstract

In situ thermal remediation (ISTR) was used to treat a vadose-zone source of trichloroethylene present at depths of 60 to 125 ft. below an occupied building at an active manufacturing facility. ISTR required innovative methods to install 135 steel casings from inside the building that included access limitations, space constraints that required angled borings and pre-modeling of rig mast positions, control measures to manage exhaust from up to four drill rigs operating simultaneously, adjustments to heater wiring to limit temperatures in shallow soils leading to indoor air heating and potential for vapor intrusion, and ensure proper positioning and trajectory of closely spaced heaters. The installed heater casings were surveyed using a Devi-Flex™ tool to monitor heater placement in casings that ranged from 87 to 196 ft. at angles between 90° and 30° from horizontal and periodically had to compensate for deflections caused by cobbles and boulders. Additional casings were installed to ensure adequate heater spacings in cases where deviations exceeded design parameters. ISTR was conducted using custom-built thermal conduction heaters designed to minimize heat output in the shallow vadose zone and inside the building while temperatures in the lower vadose zone were maintained near boiling. Cables, vapor extraction pipes, and exhaust ducts were routed overhead and through the building roof to minimize disturbance to manufacturing operations. To expedite remediation, three groups of heaters and vapor recovery wells were installed and operated in overlapping periods. The major challenges and solutions for ISTR design, construction, and operation are presented. Operations and remedial results are covered in a companion paper.