Theme: 01. Remediation Technology Innovations

Topic Area: 01q. Electrical Resistance Heating: Best Practices and Lessons Learned

Formatted Title:

Thermal Remediation in the Vicinity of Dense Utility Installation

Background/Objectives:

At many sites contaminated with chlorinated solvents, utility corridors have been discovered to be the source of a solvent release or a conduit for contaminant migration. The protection of utilities is a critical factor when designing, constructing, and operating an in situ thermal remediation (ISTR) system. A former metal finishing factory in Tennessee, impacted by chlorinated volatile organic compounds (CVOCs), faced several design challenges for installation and operation of an ISTR system, including (1) protection of numerous surface and subsurface utilities, (2) reconfiguration of surface stormwater management features to control a significant volume of stormwater, and (3) cost-effective management of drill cuttings from over 250 electrodes and temperature monitoring points. Due to the site size, the property owner also required practices to reduce the volume of hazardous waste to prevent the reclassification of the property as a large quantity generator. Subsequently, the consulting engineer and TRS Group (TRS) developed a design to support the implementation of ISTR around active utilities with significant stormwater flow, while eliminating the need for off-site hazardous waste disposal.

Approach/Activities:

The subsurface utilities included active water, natural gas and sanitary sewer lines, abandoned stainless steel horizontal dual phase extraction wells, as well as active and stagnant fire suppression lines. The majority of the subsurface utilities impacted by ISTR were present in a utility corridor along the boundary between the former metal finishing factory and a neighboring property. Because the neighboring property was an operating industrial facility, the utilities couldn’t be abandoned prior to ISTR. Design features implemented to protect the utilities included installing electrodes below the utilities, installing cooling loops around the fire suppression lines, and temperature monitoring.

The conceptual site model indicated a significant volume of contaminant was released in a vegetated stormwater channel, which was one of the 12 separate treatment areas at the site. To heat the area directly beneath the channel, the surface storm water diversion channels were constructed to divert storm water around the treatment area and allow for ISTR directly beneath the contaminated channel. The project team used the existing open volume in the contaminated channel to accept the drill cuttings from electrode installation, which eliminated the requirement for off-site disposal of the cuttings. The temporary in situ cell was chemically stabilized to facilitate drilling, followed by grading and placement of an insulated cap for thermal treatment.

Results/Lessons Learned:

TRS remediated 59,000 cubic yards of soil over an expansive industrial facility consisting of three buildings, parking lots, and a vegetated open channel. Site modifications effectively managed high levels of precipitation during construction and operation and were conducted in a cost-effective manner that eliminated the need for off-site disposal of hazardous soil cuttings. Additionally, engineering controls were installed to protect utilities and allow for a neighboring property to continue active operations. TRS extracted and thermally oxidized over 13,000 pounds of CVOCs. The presentation will focus on the technical considerations of design, construction, and operations around these challenges, describe the various tools available to manage these complexities, share lessons learned and provide the ISTR results.

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Steven Hodskins