Remediation of chemicals in low-permeability zones can be challenging, resulting in long and costly remedial timeframes. Thermal In Situ Sustainable Remediation (TISR®) can provide improved remedial outcomes for these challenging sites for a wide range of chemicals, including chlorinated solvents and aromatic hydrocarbons. By leveraging the principles of sustainable energy and advanced heat transfer technologies, TISR offers a promising solution for accelerating the remediation of impacted sites while minimizing environmental impact.

The goal of this project was to field-validate the TISR technology at a geologically challenging site impacted by chlorinated solvents. The field demonstration helped to validate TISR design and technical performance parameters and their limitations and therefore serves as a basis for wider application at other sites with challenging hydrogeology and prolonged chlorinated impacts.

TISR is an innovative and sustainable remediation technology designed to enhance the degradation of chemicals in the subsurface by increasing the temperature of the target treatment zones, thereby accelerating both biotic (microbial) and abiotic (chemical) reactions that degrade chemicals. TISR systems transfer energy to the subsurface through a closed-loop heat transfer fluid system. Subsequently, the heated fluid is circulated via insulated manifolds and process piping to the borehole heat exchangers (BHE) located in the targeted treatment area.

This project demonstrated the TISR technology to treat a chlorinated volatile organic compound (CVOC) groundwater source zone. Prior to TISR, the source zone and downgradient groundwater plume at the demonstration site was managed with enhanced in situ bioremediation (EISB) and a dynamic groundwater recirculation (pump, treat, and reinject) approach. The TISR system included 8 BHE and was designed to treat a subset of the site. The system operated from May 2022 to February 2025 and increased temperatures from an ambient average background of 17°C to a peak above 50°C at the BHE and between 20°C and 35°C in other areas. In April – May 2024, a 2% molasses substrate was injected into the TISR footprint as total organic carbon had been depleted since the previous injection event. This heating and enhanced biodegradation resulted in accelerated CVOC treatment, including a reduction of CVOCs by 2 to 4 orders of magnitude, and a decrease in the total remedial treatment time by approximately five years (assuming a five-year TISR system run time).

The specific requirements, scale, and geometry of each TISR application will vary. The monitoring infrastructure may also vary based on existing site infrastructure. However, the primary components include above-grade equipment such as a heat pump, pump station, conveyance manifold and piping, and power connection, as well as below grade BHE and monitoring infrastructure. The design and installation of the TISR system are the primary cost drivers, with a total capital cost of $724,000 for the demonstration project described herein. Annual operation and maintenance will vary depending on the energy source used in the TISR design but was approximately $40,000 per year for this demonstration project. When considered against the reduced source zone remedial timeline, TISR implementation would lead to cost avoidance of approximately $1,080,000 from reduced EISB scope. Therefore, implementation of TISR for a five-year period is estimated to reduce the total source zone remedial timeline by approximately five years for comparable cost as EISB.

When implementing TISR, it is important to recognize TISR is an enhancement strategy for optimizing source zone remedies like EISB. A critical early step is evaluating the treatment volume, as economies of scale directly influence the design and selection of energy resources needed to achieve target subsurface temperatures within a practical timeframe. This evaluation also supports a cost-benefit analysis, where accelerated chemical degradation can shorten the remedial timeline and improve return on investment (ROI). To ensure TISR is the appropriate remedy, upfront assessments of the treatment area, energy source viability, and ROI must be completed. Lessons learned from the demonstration project further emphasize the importance of sustainable energy assessments, site-specific thermal modeling, power reliability planning, and robust in situ temperature monitoring to support effective and resilient system performance. Results of this demonstration bolster operational capabilities and warfighter preparedness of by mitigating the impacts of these chemicals. (Project Completion - 2025)

Munholland, J., D. Rosso, D. Randhawa, C. Divine, and A. Pennington. 2024. Advances in Low-Temperature Thermal Remediation. In: Advances in the Characterisation and Remediation of Sites Contaminated with Petroleum Hydrocarbons: Environmental Contamination Remediation and Management (Environmental Contamination Remediation and Management Book Series); García-Rincón, J., E. Gatsios, R.J. Lenhard, E.A. Atekwana, and R. Naidu (Eds.), Springer Nature Link, 623–653. doi.org/10.1007/978-3-031-34447-3_18.

Ornelles, A., R.W. Falta, and C. Divine. 2023. A Design Tool for Solar Thermal Remediation using Borehole Heat Exchangers. Groundwater, 61(2):245–254. doi.org/10.1111/gwat.13265.

Theses and Dissertation

Ornelles, A. 2021. Development and Validation of an Analytical Modeling Tool for Solar Borehole Heat Exchangers (Master’s Thesis). Clemson University. https://tigerprints.clemson.edu/all_theses/3691.

Patents

Flanders, C., D. Randhawa, J. LaChance, and P. Visser. 2019. Thermal In-Situ Sustainable Remediation System and Method. U.S. Patent 10384246.