Formatted Title
Innovative Solutions for Implementing Thermal Treatment of a Deep TCE Source beneath an Active Facility
Background/Objectives
Vadose zone soil impacted by trichloroethene (TCE) extended from 60 to 125 feet beneath a large active manufacturing facility with more than half of the target treatment zone located below a limited-access area. The array of soil impacts which were centrally located beneath the building coupled with limited accessibility presented unique implementation challenges for remediation. This presentation focuses on the innovative solutions that were conducted to successfully construct an in situ thermal remediation system to treat the deep TCE source without interrupting the facility’s operations.
Approach/Activities
In situ thermal remediation using thermal conduction heating (TCH) technology was chosen to treat the deep source soil beneath the facility. With a significant portion of the target treatment zone located in an area where conventional vertical drilling techniques could not be used to install subsurface heater casings for TCH, borings needed to be advanced from within a 10,000‑square foot interior room having low overhead clearance and numerous structural columns. A three-dimensional visualization model was used to establish the boundaries of the treatment zone and to aid in the design and layout of a complex arrangement of 123 angled and 57 vertical heaters for thermal treatment. Heater boring lengths ranged from 87 to 196 feet and were installed at angles between 90 and 30 degrees from horizontal. Custom TCH heaters minimizing heat output in the uncontaminated soil above the target treatment zone were integrated into the design. The impediments inside the room called for a design that used a three-dimensional point cloud survey to identify potential drill rig interferences and to confirm starting locations of the heater borings prior to drilling. Advanced surveying techniques were used to align the drill rig to ensure precise starting trajectories for each of the angled boreholes along with state-of-the-art borehole surveying methods to map the exact trajectory of each constructed angled heater casing.
Results/Lessons Learned
The innovative solutions used to overcome the identified challenges resulted in meeting the project delivery requirements, including effective remediation of the deep TCE source zone without interruptions to the facility’s business operations. Verifying the heater casing trajectory was paramount for documenting that the installation was within the maximum heater spacing tolerance limits, and real-time adjustments to succeeding adjacent heater borings were conducted to compensate or additional heaters were added to ensure effective heating throughout the target treatment zone. Custom TCH heaters minimizing heat output in the uncontaminated soil above the target treatment zone resulted in significant energy savings and reduced heat transfer into the building interior.