Per- and polyfluoroalkyl substances (PFAS) are resistant to most biotic and abiotic degradation processes and therefore accumulate in the environment. This project investigated the thermal conduction heating (TCH) remediation performed by TRS Group, Inc. (TRS), in conjunction with Paragon Professional Services, LLC and Brown University at Eielson Air Force Base, located near Fairbanks, AK. Using TRS’s patented FlexHeater® TCH technology, the removal of PFAS from ex situ soil stockpiles was demonstrated.

During TCH application, the heater itself was raised to temperatures up to 900°C. The radiant heat from the FlexHeater® then heated the casing and the surrounding soil is then slowly heated by conduction. The PFAS-containing soil was heated to a minimum temperature of 350°C throughout the treatment volume. Soil vapor extraction (SVE) screens were installed in between the heater casings. The SVE screens were put under vacuum using a positive displacement blower. Recovered steam and soil vapors were then transported via stainless steel piping headers to a wet scrubber and a condenser and on to a vapor/liquid separator and heat exchanger. Condensate and non-condensable air were treated using sorbent filtration.

Soil sampling performed before and after thermal treatment showed substantial reductions in PFAS, including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). The predominant PFAS, PFOS, experienced a 95.3% average percent reduction from thermal treatment. All soil samples collected post thermal treatment were below detection limits for PFOA. Post thermal treatment soil showed a PFOS concentrations average of 4.1 µg/kg, with the highest levels found at the top of the pile where the soil reached 350^oC. Samples heated to 400^oC were below Alaska Department of Environmental Conservation soil cleanup levels for PFOA and PFOS, 1.7 μg/kg and 3.0 μg/kg, respectively. The implementation cost of the technology was evaluated for soil volumes up to 15,000 cubic yards (yd³). Treatment costs ranging from $550-800 per cubic yard are projected, with lower unit costs for large volumes. Site location (climate and mobilization distance) and local electricity costs were identified as the main cost drivers.

For future ex situ PFAS soil treatments, sufficient power availability and reliability are important considerations when considering implementation. If sufficient power is not available, additional electricity sources can be installed; however, scheduling and funding evaluations should be performed to assess project feasibility. Water source availability for the vapor and liquid treatment process equipment should be considered for implementation. Treated process water discharge and treated vapor emission requirements are also important implementation issues to consider to ensure the sampling. Results of this demonstration bolster operational capabilities and warfighter preparedness of by mitigating the impacts of these chemicals. (Project Completion - 2024)