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(/* Stockpile Treatment, Eielson AFB, Alaska (ESTCP project ER20-5198Crownover, E., Heron, G., Pennell, K., Ramsey, B., Rickabaugh, T., Stallings, P., Stauch, L., Woodcock, M., 2023. Ex Situ Thermal Treatment of PFAS-Impacted Soils, Final Report. Eiels...)
 
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==Sediment Capping==
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==Thermal Conduction Heating for Treatment of PFAS-Impacted Soil==  
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Capping® is an ''in situ'' remedial technology that involves placement of a clean substrate on the surface of [[Contaminated Sediments - Introduction | contaminated sediments]] to reduce contaminant uptake by benthic organisms and contaminant flux to surface water. Simple sand caps can be effective in reducing exposure of benthic organisms and in limiting oxygen transport into the contaminated sediments, resulting in precipitation of metal sulfides. Amendments are sometimes included in caps to reduce cap permeability and groundwater upwelling, to increase contaminant sorption or biodegradation, or to improve habitat.   
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Removal of [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]] compounds from impacted soils is challenging due to the modest volatility and varying properties of most PFAS compounds. Thermal treatment technologies have been developed for treatment of semi-volatile compounds in soils such as dioxins, furans, poly-aromatic hydrocarbons and poly-chlorinated biphenyls at temperatures near 325&deg;C. In controlled bench-scale testing, complete removal of targeted PFAS compounds to concentrations below reporting limits of 0.5 µg/kg was demonstrated at temperatures of 400&deg;C<ref name="CrownoverEtAl2019"> Crownover, E., Oberle, D., Heron, G., Kluger, M., 2019.  Perfluoroalkyl and polyfluoroalkyl substances thermal desorption evaluation. Remediation Journal, 29(4), pp. 77-81. [https://doi.org/10.1002/rem.21623 doi: 10.1002/rem.21623]</ref>. Three field-scale thermal PFAS treatment projects that have been completed in the US include an in-pile treatment demonstration, an ''in situ'' vadose zone treatment demonstration and a larger scale treatment demonstration with excavated PFAS-impacted soil in a constructed pile. Based on the results, thermal treatment temperatures of at least 400&deg;C and a holding time of 7-10 days are recommended for reaching local and federal PFAS soil standards. The energy requirement to treat typical wet soil ranges from 300 to 400 kWh per cubic yard, exclusive of heat losses which are scale dependent. Extracted vapors have been treated using condensation and granular activated charcoal filtration, with thermal and catalytic oxidation as another option which is currently being evaluated for field scale applications. Compared to other options such as soil washing, the ability to treat on site and to treat all soil fractions is an advantage.   
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
  
 
'''Related Article(s):'''
 
'''Related Article(s):'''
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*[[Contaminated Sediments - Introduction]]
 
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*[[In Situ Treatment of Contaminated Sediments with Activated Carbon]]
 
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*Sediment Risk Assessment
 
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*[[Passive Sampling of Sediments]]
 
  
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'''Contributor(s):'''
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*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
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*Danny Reible
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*[[Thermal Conduction Heating (TCH)]]
  
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'''Key Resource(s):'''
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'''Contributors:''' Gorm Heron, Emily Crownover, Patrick Joyce, Ramona Iery
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*Processes, Assessment and Remediation of Contaminated Sediments<ref name="Reible2014">Reible, D. D., Editor, 2014. Processes, Assessment and Remediation of Contaminated Sediments. Springer, New York, NY. 462 pp. ISBN: 978-1-4614-6725-0</ref>
 
  
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* Guidance for In-Situ Subaqueous Capping of Contaminated Sediments<ref name="Palermo1998">Palermo, M., Maynord, S., Miller, J. and Reible, D., 1998. Guidance for In-Situ Subaqueous Capping of Contaminated Sediments. Assessment and Remediation of Contaminated Sediments (ARCS) Program, Great Lakes National Program Office, US EPA 905-B96-004. 147 pp.  [[Media: USEPA_905-B96-004.pdf | Report.pdf]]</ref>
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'''Key Resource:'''
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*Perfluoroalkyl and polyfluoroalkyl substances thermal desorption evaluation<ref name="CrownoverEtAl2019"/>
  
 
==Introduction==
 
==Introduction==
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[[File:SedCapFig1.png|thumb|left|470px|Figure 1. Conceptual sketch of a cap configuration]]
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[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]] have become prominent emerging contaminants in soil and groundwater. Soil source zones have been identified at locations where the chemicals were produced, handled or used. Few effective options exist for treatments that can meet local and federal soil standards. Over the past 30 plus years, thermal remediation technologies have grown from experimental and innovative prospects to mature and accepted solutions deployed effectively at many sites. More than 600 thermal case studies have been summarized by Horst and colleagues<ref name="HorstEtAl2021">Horst, J., Munholland, J., Hegele, P., Klemmer, M., Gattenby, J., 2021. In Situ Thermal Remediation for Source Areas: Technology Advances and a Review of the Market From 1988–2020. Groundwater Monitoring & Remediation, 41(1), p. 17. [https://doi.org/10.1111/gwmr.12424 doi: 10.1111/gwmr.12424]&nbsp; [[Media: gwmr.12424.pdf | Open Access Manuscript]]</ref>. [[Thermal Conduction Heating (TCH)]] has been used for higher temperature applications such as removal of [[1,4-Dioxane]]. This article reports recent experience with TCH treatment of PFAS-impacted soil.
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Capping is an ''in situ'' remedial technology for contaminated sediments that involves placement of a clean substrate on the sediment surface.  Capping contaminated sediments following [[Wikipedia: Dredging | dredging operations]] and capping of dredged material to stabilize contaminants has been a common practice by the United States Army Corps of Engineers since the 1970s. Beginning in the 1980s, in Japan and subsequently elsewhere, capping has been used more widely as a remedial approach to improve the quality of the bottom substrate and reduce contaminant exposures to benthic organisms and fish. The USEPA published a capping guidance document in 1998 that summarizes past uses of sediment capping and outlines its basic design<ref name="Palermo1998"/>.   Although capping technology has developed substantially in the past 20 years, this early reference still provides useful information on the approach and its applications.  A more recent summary of capping is described in Reible 2014<ref name="Reible2014"/>.
 
  
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Capping serves to contain contaminated sediment solids, isolate contaminants from benthic organisms and reduce contaminant transport to the sediment surface and overlying water. The clean substrate may be an inert material such as sand, a natural sorbing material such as other sediments or clays, or be amended with an active/reactive material to enhance the isolation of the contaminants. Amendments to enhance contaminant isolation include permeability reduction agents to divert groundwater flow, sorbents to retard contaminant migration through the capping layer or provide greater accumulation capacity, or reagents to encourage degradation or transformation of the contaminants.  
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==Target Temperature and Duration==
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PFAS behave differently from most other organics subjected to TCH treatment. While the boiling points of individual PFAS fall in the range of 150-400&deg;C, their chemical and physical behavior creates additional challenges. Some PFAS form ionic species in certain pH ranges and salts under other chemical conditions. This intricate behavior and our limited understanding of what this means for our ability to remove the PFAS from soils means that direct testing of thermal treatment options is warranted. Crownover and colleagues<ref name="CrownoverEtAl2019"/> subjected PFAS-laden soil to bench-scale heating to temperatures between 200 and 400&deg;C which showed strong reductions of PFAS concentrations at 350&deg;C and complete removal of many PFAS compounds at 400&deg;C. The soil concentrations of targeted PFAS were reduced to nearly undetectable levels in this study.
  
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The basic concept of a cap is illustrated in Figure 1.  The Figure also illustrates that a cap is often a thin layer or layers relative to water depth and generally causes little disturbance to the underlying sediments or body of water in which it is placed.   Depending upon the erosive forces to which the cap may be subjected, the surface layer may be composed of relatively coarse material to withstand those erosive forces.  
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==Heating Method==
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For semi-volatile compounds such as dioxins, furans, poly-chlorinated biphenyls (PCBs) and Poly-Aromatic Hydrocarbons (PAH), thermal conduction heating has evolved as the dominant thermal technology because it is capable of achieving soil temperatures higher than the boiling point of water, which are necessary for complete removal of these organic compounds. Temperatures between 200 and 500&deg;C have been required to achieve the desired reduction in contaminant concentrations<ref name="StegemeierVinegar2001">Stegemeier, G.L., Vinegar, H.J., 2001. Thermal Conduction Heating for In-Situ Thermal Desorption of Soils. Ch. 4.6, pp. 1-37. In: Chang H. Oh (ed.), Hazardous and Radioactive Waste Treatment Technologies Handbook, CRC Press, Boca Raton, FL. ISBN 9780849395864 [[Media: StegemeierVinegar2001.pdf | Open Access Article]]</ref>. TCH has become a popular technology for PFAS treatment because temperatures in the 400&deg;C range are needed.
  
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Although a cap is typically thin compared to the water depth, it generally must be thicker than the biologically active zone (BAZ) of the sediments.  The biologically active zone is that zone in which benthic organisms live and interact with the sediment.  Their activities tend to mix the BAZ (known as [[Wikipedia: Bioturbation | bioturbation]]) over the course of a few years and thus a cap that is thinner than the BAZ will tend to become intermixed with the underlying contaminated sediments.   Processes other than bioturbation including diffusion, advection or groundwater upwelling, hyporheic exchange near the interface, biogenic gas production and migration and underlying sediment consolidation can all lead to contaminant migration into and through a cap.  These occur at different rates and intensities and their assessment and evaluation ultimately governs the effectiveness of a cap and the feasibility of its use as a sediment remediation technology for a particular site.
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The energy source for TCH can be electricity (most commonly used), or fossil fuels (typically gas, diesel or fuel oil). Electrically powered TCH offers the largest flexibility for power input which also can be supplied by renewable and sustainable energy sources.
  
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In general, capping is an effective remedial technology for contaminants that are strongly associated with the sediment solids including hydrophobic organic compounds such as high molecular weight [[Polycyclic Aromatic Hydrocarbons (PAHs) | polycyclic aromatic hydrocarbons (PAHs)]], [[Wikipedia: Polychlorinated biphenyl | polychlorinated biphenyls (PCBs)]], [[Wikipedia: Dioxins and dioxin-like compounds | dioxins]] and [[Wikipedia: DDT | DDTx]], but also [[Metal and Metalloid Contaminants | heavy metals]].  Hydrophobic organic compounds tend to strongly associate with the organic fraction of sediments so organic rich sediments or the addition of organic phases to the capping material can be very effective at containing these contaminants. Many of the common heavy metals of concern, including cadmium, copper, nickel, zinc, lead and mercury, tend to be associated with insoluble sulfides under strongly reducing conditions. Since oxygen penetration into a capping layer is typically limited to a few cm or less at the surface, a cap serves to drive the underlying contaminated sediment toward strongly reducing conditions and, particularly in marine and estuarine sediments, encourage sulfate reduction leading to the formation of these insoluble sulfides.  The low solubility of these sulfides encourages retention by a capping layer and makes the cap extremely effective as a remedial approach for sediments with elevated concentrations of heavy metals.
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==Energy Usage==
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Treating PFAS-impacted soil with heat requires energy to first bring the soil and porewater to the boiling point of water, then to evaporate the porewater until the soil is dry, and finally to heat the dry soil up to the target treatment temperature. The energy demand for wet soils falls in the 300-400 kWh/cy range, dependent on porosity and water saturation. Additional energy is consumed as heat is lost to the surroundings and by vapor treatment equipment, yielding a typical usage of 400-600 kWh/cy total for larger soil treatment volumes. Wetter soils and small treatment volumes drive the energy usage towards the higher number, whereas larger soil volumes and dry soil can be treated with less energy.   
  
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A variety of tools have been developed to evaluate the processes leading to sorption and retardation of contaminants as well as processes leading to contaminant migration and release. The original references quantifying contaminant behavior in a sediment cap were explored in a series of papers in the early 1990s<ref name="Wang1991">Wang, X.Q., Thibodeaux, L.J., Valsaraj, K.T. and Reible, D.D., 1991. Efficiency of Capping Contaminated Bed Sediments in Situ. 1. Laboratory-Scale Experiments on Diffusion-Adsorption in the Capping Layer. Environmental Science and Technology, 25(9), pp.1578-1584.  [https://doi.org/10.1021/es00021a008 DOI: 10.1021/es00021a008]</ref><ref name="Thoma1993">Thoma, G.J., Reible, D.D., Valsaraj, K.T. and Thibodeaux, L.J., 1993. Efficiency of Capping Contaminated Bed Sediments in Situ 2. Mathematics of Diffusion-Adsorption in the Capping Layer. Environmental Science and Technology, 27(12), pp.2412-2419.  [https://doi.org/10.1021/es00048a015 DOI: 10.1021/es00048a015]</ref>.  Since that time, design tools have been continuously improved. [https://www.depts.ttu.edu/ceweb/research/reiblesgroup/downloads.php CapSim] is a commonly used and current tool developed by Dr. Reible and collaborators. This tool can evaluate contaminant release from uncapped, capped, and treated sediments for purposes of design and evaluation.  The model formulation and structure is described in Shen et al. 2018<ref name="Shin2018">Shen, X., Lampert, D., Ogle, S. and Reible, D., 2018. A software tool for simulating contaminant transport and remedial effectiveness in sediment environments. Environmental Modelling and Software, 109, pp. 104-113.  [https://doi.org/10.1016/j.envsoft.2018.08.014 DOI: 10.1016/j.envsoft.2018.08.014]</ref>. One common use of such a tool is to evaluate the effect of various cap materials and thicknesses on the performance of a cap.
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==Vapor Treatment==
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During the TCH process a significant fraction of the PFAS compounds are volatilized by the heat and then removed from the soil by vacuum extraction. The vapors must be treated and eventually discharged while meeting local and/or federal standards. Two types of vapor treatment have been used in past TCH applications for organics: (1) thermal and catalytic oxidation and (2) condensation followed by granular activated charcoal (GAC) filtration. Due to uncertainties related to thermal destruction of fluorinated compounds and future requirements for treatment temperature and residence time, condensation and GAC filtration have been used in the first three PFAS treatment field demonstrations. It should be noted that PFAS compounds will stick to surfaces and that decontamination of the equipment is important. This could generate additional waste as GAC vessels, pipes and other wetted equipment need careful cleaning with solvents or rinsing agents such as PerfluorAd<sup><small>TM</small></sup>.  
  
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==Cap Design and Materials for Chemical Containment==
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==PFAS Reactivity and Fate==
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An inert material such as sand can be effective as a capping material where contaminants are strongly associated with solids and where the operative site specific transport mechanisms do not lead to rapid contaminant migration through such a material. Additional contaminant containment can often be achieved through the placement of clean sediment, e.g. dredged material from a nearby location.  Other materials as cap layers or amendments may be useful to address particularly mobile contaminants or when particular degradative mechanisms can be exploited. The Anacostia River was the site of a demonstration that first tested “active” or “amended” capping in the field<ref name="Reible2003">Reible, D., Constant, D.W., Roberts, K. and Zhu, Y., 2003. Active capping demonstration project in anacostia DC. In Second International Conference on the Remediation of Contaminated Sediments: October.  Free download available from: [https://www.researchgate.net/profile/Danny-Reible/publication/237747790_ACTIVE_CAPPING_DEMONSTRATION_PROJECT_IN_ANACOSTIA_DC/links/0c96053861030b7699000000/ACTIVE-CAPPING-DEMONSTRATION-PROJECT-IN-ANACOSTIA-DC.pdf ResearchGate]</ref><ref name="Reible2006">Reible, D., Lampert, D., Constant, D., Mutch Jr, R.D. and Zhu, Y., 2006. Active Capping Demonstration in the Anacostia River, Washington, DC. Remediation Journal: The Journal of Environmental Cleanup Costs, Technologies and Techniques, 17(1), pp. 39-53.  [https://doi.org/10.1002/rem.20111 DOI: 10.1002/rem.20111]  Free download available from: [https://www.academia.edu/download/44146457/Remediation_Journal_Paper_2006.pdf Academia.edu]</ref>. Amended caps are often the best option when groundwater upwelling or other advective processes promote significant mobility of contaminants and the addition of sorbents can slow that contaminant migration<ref name="Ghosh2011">Ghosh, U., Luthy, R.G., Cornelissen, G., Werner, D. and Menzie, C.A., 2011. In-situ Sorbent Amendments: A New Direction in Contaminated Sediment Management. Environmental Science and Technology, 45(4), pp. 1163-1168. [https://doi.org/10.1021/es102694h DOI: 10.1021/es102694h] Open access article from: [https://pubs.acs.org/doi/pdf/10.1021/es102694h American Chemical Society]&nbsp;&nbsp; [[Media: Ghosh2011.pdf | Report.pdf]]</ref>. Although a variety of materials have been proposed for sediment caps, a far smaller number of options have been successfully employed in the field.  
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While evaluating initial soil treatment results, Crownover ''et al''<ref name="CrownoverEtAl2019"/> noted the lack of complete data sets when the soils were analyzed for non-targeted compounds or extractable precursors. Attempts to establish the fluorine balance suggest that the final fate of the fluorine in the PFAS is not yet fully understood. Transformations are likely occurring in the heated soil as demonstrated in laboratory experiments with and without calcium hydroxide (Ca(OH)<small><sub>2</sub></small>) amendment<ref>Koster van Groos, P.G., 2021. Small-Scale Thermal Treatment of Investigation-Derived Wastes Containing PFAS. [https://serdp-estcp.mil/ Strategic Environmental Research and Development Program (SERDP) - Environmental Security Technology Certification Program (ESTCP)], [https://serdp-estcp.mil/projects/details/2f1577ac-c8ea-4ae8-804e-c9f97a12edb3/small-scale-thermal-treatment-of-investigation-derived-wastes-idw-containing-pfas Project ER18-1556 Website], [[Media: ER18-1556_Final_Report.pdf | Final Report.pdf]]</ref>. Amendments such as Ca(OH)<sub><small>2</small></sub> may be useful in reducing the required treatment temperature by catalyzing PFAS degradation. With thousands of PFAS potentially present, the interactions are complex and may never be fully understood. Therefore, successful thermal treatment may require a higher target temperature than for other organics with similar boiling points – simply to provide a buffer against the uncertainty.   
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Metals migration is very site dependent due to the potential for many metals to complex with other species in the interstitial water and the specific metal speciation present at a site. Often, the strongly reducing environment beneath a cap renders many common metals unavailable through the formation of metal sulfides.  In such cases, a simple sand cap can be very effective.  Amended caps to manage metal contaminated sediments may be advantageous when site specific conditions lead to elevated metals mobility, but should be supported with site specific testing<ref name="Viana2008">Viana, P.Z., Yin, K. and Rockne, K.J., 2008. Modeling Active Capping Efficacy. 1. Metal and Organometal Contaminated Sediment Remediation. Environmental Science and Technology, 42(23), pp. 8922-8929. [https://doi.org/10.1021/es800942t DOI: 10.1021/es800942t]</ref>.
 
  
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For hydrophobic organic contaminants, cap amendments that directly control groundwater upwelling and also sorbents that can remove migrating contaminants from that groundwater have been successfully employed.   Examples include clay materials such as AquaBlok<sup>&reg;</sup> for permeability control, sorbents such as [[Wikipedia: Activated carbon | activated carbon]] for truly dissolved contaminants, and [[Wikipedia: Organoclay | organophilic clays]] for separate phase contaminants.
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==Case Studies==
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===Stockpile Treatment, Eielson AFB, Alaska ([https://serdp-estcp.mil/projects/details/62098505-de86-43b2-bead-ae8018854141 ESTCP project ER20-5198]<ref name="CrownoverEtAl2023">Crownover, E., Heron, G., Pennell, K., Ramsey, B., Rickabaugh, T., Stallings, P., Stauch, L., Woodcock, M., 2023. Ex Situ Thermal Treatment of PFAS-Impacted Soils, [[Media: ER20-5198 Final Report.pdf | Final Report.]] Eielson Air Force Base, Alaska. [https://serdp-estcp.mil/ Strategic Environmental Research and Development Program (SERDP) - Environmental Security Technology Certification Program (ESTCP)], [https://serdp-estcp.mil/projects/details/62098505-de86-43b2-bead-ae8018854141 Project ER20-5198 Website]</ref>)===
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[[File: HeronFig1.png | thumb | 400 px | Figure 1. TCH treatment of a PFAS-laden stockpile at Eielson AFB, Alaska<ref name="CrownoverEtAl2023"/>]]
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Since there has been no approved or widely accepted method for treating soils impacted by PFAS, a common practice has been to excavate PFAS-impacted soil and place it in lined stockpiles. Eielson AFB in Alaska is an example where approximately 50 stockpiles were constructed to temporarily store 150,000 cubic yards of soil. One of the stockpiles containing 134 cubic yards of PFAS-impacted soil was heated to 350-450&deg;C over 90 days (Figure 1). Volatilized PFAS was extracted from the soil using vacuum extraction and treated via condensation and filtration by granular activated charcoal. Under field conditions, PFAS concentration reductions from 230 µg/kg to below 0.5 µg/kg were demonstrated for soils that reached 400&deg;C or higher for 7 days. These soils achieved the Alaska soil standards of 3 µg/kg for PFOS and 1.7 µg/kg for PFOA. Cooler soils near the top of the stockpile had remaining PFOS in the range of 0.5-20 µg/kg with an overall average of 4.1 µg/kg. Sampling of all soils heated to 400&deg;C or higher demonstrated that the soils achieved undetectable levels of targeted PFAS (typical reporting limit was 0.5 µg/kg).
  
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The placement of clean sediment as an ''in situ'' cap can be difficult when the material is fine grained or has a low density. Capping with a layer of coarse grained material such as clean sand mitigates this issue although clean sands have minimal sorption capacity.  Because of this limitation, sand caps may not be sufficient for achieving remedial goals in sites where contamination levels are high or transport rates are fast due to pore water upwelling or tidal pumping effects. Conditions such as these may require the use of “active” amendments to reduce transport rates.  
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===''In situ'' Vadose Zone Treatment, Beale AFB, California ([https://serdp-estcp.mil/projects/details/94949542-f9f7-419d-8028-8ba318495641/er20-5250-project-overview ESTCP project ER20-5250]<ref name="Iery2024">Iery, R. 2024. In Situ Thermal Treatment of PFAS in the Vadose Zone. [https://serdp-estcp.mil/ Strategic Environmental Research and Development Program (SERDP) - Environmental Security Technology Certification Program (ESTCP)], [https://serdp-estcp.mil/projects/details/94949542-f9f7-419d-8028-8ba318495641 Project ER20-5250 Website]. [[Media: ER20-5250 Fact Sheet.pdf | Fact Sheet.pdf]]</ref>)===
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[[File: HeronFig2.png | thumb | 600 px | Figure 2. ''In situ'' TCH treatment of a PFAS-rich vadose zone hotspot at Beale AFB, California]]
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Capping with clean sand provides a physical barrier between the underlying contaminated material and the overlying water, stabilizes the underlying sediment to prevent re-suspension of contaminated particles, and can reduce chemical exposure under certain conditions. Sand primarily provides a passive barrier to the downward penetration of bioturbating organisms and the upward movement of sediment or contaminants. Although conventional sandy caps can often be an effective means of managing contaminated sediments, there are conditions when sand caps may not be capable of achieving design objectives.  Some factors that reduce the effectiveness of sand caps include:
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A former fire-training area at Beale AFB had PFAS concentrations as high as 1,970 µg/kg in shallow soils.  In situ treatment of a PFAS-rich soil was demonstrated using 16 TCH borings installed in the source area to a depth of 18 ft (Figure 2). Soils which reached the target temperatures were reduced to PFAS concentrations below 1 µg/kg. Perched water which entered in one side of the area delayed heating in that area, and soils which were affected had more modest PFAS concentration reductions. As a lesson learned, future in situ TCH treatments will include provisions for minimizing water entering the treated volume<ref name="Iery2024"/>. It was demonstrated that with proper water management, even highly impacted soils can be treated to near non-detect concentrations (greater than 99% reduction).   
  
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*erosion and loss of cap integrity
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===Constructed Pile Treatment, JBER, Alaska ([https://serdp-estcp.mil/projects/details/eb7311db-6233-4c7f-b23a-e003ac1926c5/pfas-treatment-in-soil-using-thermal-conduction-heating ESTCP Project ER23-8369]<ref name="CrownoverHeron2024">Crownover, E., Heron, G., 2024. PFAS Treatment in Soil Using Thermal Conduction Heating. Defense Innovation Unit (DIU) and [https://serdp-estcp.mil/ Strategic Environmental Research and Development Program (SERDP) - Environmental Security Technology Certification Program (ESTCP)],  [https://serdp-estcp.mil/projects/details/eb7311db-6233-4c7f-b23a-e003ac1926c5/pfas-treatment-in-soil-using-thermal-conduction-heating Project ER23-8369 Website]</ref>)===
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*high groundwater upwelling rates
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[[File: HeronFig3.png | thumb | 600 px | Figure 3. Treatment of a 2,000 cubic yard soil pile at JBER, Alaska]]
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*mobile (low sorption) contaminants of concern (COCs)
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In 2024, a stockpile of 2,000 cubic yards of PFAS-impacted soil was thermally treated at Joint Base Elmendorf-Richardson (JBER) in Anchorage, Alaska<ref name="CrownoverHeron2024"/>. This ESTCP project was implemented in partnership with DOD’s Defense Innovation Unit (DIU). Three technology demonstrations were conducted at the site where approximately 6,000 cy of PFAS-impacted soil was treated (TCH, smoldering and kiln-style thermal desorption). Figure 3 shows the fully constructed pile used for the TCH demonstration. In August 2024 the soil temperature for the TCH treatment exceeded 400&deg;C in all monitoring locations. At an energy density of 355 kWh/cy, Alaska Department of Environmental Conservation (ADEC) standards and EPA Residential Regional Screening Levels (RSLs) for PFAS in soil were achieved. At JBER, all 30 post-treatment soil samples were near or below detection limits for all targeted PFAS compounds using EPA Method 1633. The composite of all 30 soil samples was below all detection limits for EPA Method 1633. Detection limits ranged from 0.0052 µg/kg to 0.19 µg/kg.
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*high COC concentrations
 
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*unusually toxic COCs
 
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*the presence of tidal influences
 
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*the presence of non-aqueous phase liquids (NAPLs)
 
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*high rates of gas ebullition
 
  
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Of these, the first three are common limitations to capping and often control the ability to effectively design and implement a cap as a sediment remedial strategy. In these cases, it may be possible to offset these issues by increasing the thickness of the cap.  However, the required thickness can reach infeasible levels in shallow streams or navigable water bodies.  In addition, increased construction costs associated with thick caps may become prohibitive.  As a result of these issues, caps that use alternative materials (also known as active caps) to reduce the thickness or increase the protectiveness of a cap may be necessary. The materials in active caps are designed to interact with the COCs to enhance the containment properties of the cap.  
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==Advantages and Disadvantages==
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Thermal treatment of PFAS in soils is energy intensive, and the cost of that energy may be prohibitive for some clients. Also, while it often is the least costly option for complete PFAS removal when compared to excavation followed by offsite disposal or destruction, heating soil to treatment temperatures on site or ''in situ'' typically takes longer than excavation. Major advantages include:
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*On site or ''in situ'' treatment eliminates the need to transport and dispose of the contaminated soil
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*Site liabilities are removed once and for all
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*Treatment costs are competitive with excavation, transportation and off-site treatment or disposal.
  
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[[Wikipedia: Apatite | Apatites]] are a class of naturally occurring minerals that have been investigated as a sorbent for metals in soils and sediments<ref name="Melton2003">Melton, J.S., Crannell, B.S., Eighmy, T.T., Wilson, C. and Reible, D.D., 2003. Field Trial of the UNH Phosphate-Based Reactive Barrier Capping System for the Anacostia River. EPA Grant R819165-01-0</ref><ref name="Reible2003"/><ref name="Knox2012">Knox, A.S., Paller, M.H. and Roberts, J., 2012. Active Capping Technology—New Approaches for In Situ Remediation of Contaminated Sediments. Remediation Journal, 22(2), pp.93-117.  [https://doi.org/10.1002/rem.21313 DOI: 10.1002/rem.21313]  Free download available from: [https://www.researchgate.net/profile/Anna-Knox-2/publication/233374607_Active_Capping_Technology-New_Approaches_for_In_Situ_Remediation_of_Contaminated_Sediments/links/5a7de4c5aca272a73765c344/Active-Capping-Technology-New-Approaches-for-In-Situ-Remediation-of-Contaminated-Sediments.pdf ResearchGate]</ref>.  Apatites consist of a matrix of calcium phosphate and various other common anions, including fluoride, chloride, hydroxide, and occasionally carbonate. Metals are sequestered either through direct ion exchange with the calcium atom or dissolution of hydroxyapatite followed by precipitation of lead apatite.  [[Wikipedia: Zeolite | Zeolites]], which are microporous aluminosilicate minerals with a high cationic exchange capacity (CEC), have also been proposed to manage metal species<ref name="Zhan2019">Zhan, Y., Yu, Y., Lin, J., Wu, X., Wang, Y. and Zhao, Y., 2019. Simultaneous control of nitrogen and phosphorus release from sediments using iron-modified zeolite as capping and amendment materials. Journal of Environmental Management, 249, p.109369.  [https://doi.org/10.1016/j.jenvman.2019.109369 DOI: 10.1016/j.jenvman.2019.109369]</ref>.
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==Recommendations==
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Recent research suggests:
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It is possible to create a hydrophobic, sorbing layer for non-polar organics by exchanging a cationic surfactant onto the surface of clays such as zeolites and bentonites,. Organoclay is a modified bentonite containing such substitutions that has been evaluated for control of non-aqueous phase NAPLs and other organic contaminants<ref name="Reible2007">Reible, D.D., Lu, X., Moretti, L., Galjour, J. and Ma, X., 2007. Organoclays for the capping of contaminated sediments. AIChE Annual Meeting.  ISBN: 978-081691022-9</ref>.  An organoclay cap has been implemented for sediment remediation at the McCormick and Baxter site in Portland, OR<ref name="Parrett2005">Parrett, K. and Blishke, H., 2005. 23-Acre Multilayer Sediment Cap in Dynamic Riverine Environment Using Organoclay an Adsorptive Capping Material. Presentation to Society of Environmental Toxicology and Chemistry (SETAC), 26th Annual Meeting.</ref>.  A similar organic sorbing phase can be formed by treating zeolites with surfactants but this approach has not been reported for contaminated sediments.
+
*Successful thermal treatment of PFAS may require a higher target temperature than for other organics with similar boiling points
−
 
+
*Prevention of influx of water into treatment zone may be necessary.
−
Activated carbon is a strong sorbent of hydrophobic organic compounds and has been used as a [[In Situ Treatment of Contaminated Sediments with Activated Carbon | treatment for sediments]] or as an active sorbent within a capping layer<ref name="Zimmerman2004">Zimmerman, J.R., Ghosh, U., Millward, R.N., Bridges, T.S. and Luthy, R.G., 2004. Addition of Carbon Sorbents to Reduce PCB and PAH Bioavailability in Marine Sediments: Physicochemical Tests. Environmental Science and Technology, 38(20), pp. 5458-5464.  [https://doi.org/10.1021/es034992v DOI: 10.1021/es034992v]</ref><ref name="Werner2005">Werner, D., Higgins, C.P. and Luthy, R.G., 2005. The sequestration of PCBs in Lake Hartwell sediment with activated carbon. Water Research, 39(10), pp. 2105-2113.  [https://doi.org/10.1016/j.watres.2005.03.019 DOI: 10.1016/j.watres.2005.03.019]</ref><ref name="Abel2018">Abel, S. and Akkanen, J., 2018. A Combined Field and Laboratory Study on Activated Carbon-Based Thin Layer Capping in a PCB-Contaminated Boreal Lake. Environmental Science and Technology, 52(8), pp. 4702-4710. [https://doi.org/10.1021/acs.est.7b05114 DOI: 10.1021/acs.est.7b05114] Open access article available from: [https://pubs.acs.org/doi/pdf/10.1021/acs.est.7b05114 American Chemical Society]&nbsp;&nbsp; [[Media: Abel2018.pdf | Report.pdf]]</ref><ref name="Payne 2018">Payne, R.B., Ghosh, U., May, H.D., Marshall, C.W. and Sowers, K.R., 2019. A Pilot-Scale Field Study: In Situ Treatment of PCB-Impacted Sediments with Bioamended Activated Carbon. Environmental Science and Technology, 53(5), pp. 2626-2634. [https://doi.org/10.1021/acs.est.8b05019 DOI: 10.1021/acs.est.8b05019]</ref><ref name="Yan2020">Yan, S., Rakowska, M., Shen, X., Himmer, T., Irvine, C., Zajac-Fay, R., Eby, J., Janda, D., Ohannessian, S. and Reible, D.D., 2020. Bioavailability Assessment in Activated Carbon Treated Coastal Sediment with In situ and Ex situ Porewater Measurements. Water Research, 185, p. 116259.  [https://doi.org/10.1016/j.watres.2020.116259 DOI: 10.1016/j.watres.2020.116259]</ref>.  Placement of activated carbon for sediment capping is difficult due to the near neutral buoyancy of the material but it has been applied in this manner in relatively low energy environments such as Onondaga Lake, Syracuse, NY<ref name="Vlassopoulos2017">Vlassopoulos, D., Russell, K., Larosa, P., Brown, R., Mohan, R., Glaza, E., Drachenberg, T., Reible, D., Hague, W., McAuliffe, J. and Miller, S., 2017. Evaluation, Design, and Construction of Amended Reactive Caps to Restore Onondaga Lake, Syracuse, New York, USA. Journal of Marine Environmental Engineering, 10(1), pp. 13-27.  Free download available from: [https://www.researchgate.net/publication/317762995_Evaluation_design_and_construction_of_amended_reactive_caps_to_restore_Onondaga_lake_Syracuse_New_York_USA ResearchGate]</ref>.  Alternatives in higher energy environments include placement of activated carbon in a mat such as the CETCO Reactive Core Mat (RCM)<sup>&reg;</sup> or Huesker Tektoseal<sup>&reg;</sup>, or as a composite material such as SediMite<sup>&reg;</sup> or AquaGate<sup>&reg;</sup>.  In the case of the mats, powdered or granular activated carbon can be placed in a controlled layer while the density of the composite materials is such that they can be broadcast from the surface and allowed to settle to the bottom.  In a sediment treatment application, the composite material would either be worked into the surface or allowed to intermix gradually by bioturbation and other processes.  In a capping application, the mat or composite material would typically be combined or overlain with a sand or other capping layer to keep it in place and to provide a chemical isolation layer away from the sediment surface.
+
Future studies should examine the potential for enhanced degradation during the thermal process by using soil amendments and/or manipulation of the local geochemistry to reduce the required treatment temperatures and therefore also reduce energy demand.
−
 
 
−
As an alternative to a sorptive capping amendment, low-permeability cap amendments have been proposed to enhance cap design life by decreasing pore water advection.  Low permeability clays are an effective means to divert upwelling groundwater away from a contaminated sediment area but are difficult to place in the aqueous environment.  Bentonite clays can be placed in mats similar to what is done to provide a low permeability liner in landfills. There are also commercial products that can place clays directly such as the composite material AquaBlok<sup>&reg;</sup>, a bentonite clay and polymer based mineral around an aggregate core<ref name="Barth2008">Barth, E.F., Reible, D. and Bullard, A., 2008. Evaluation of the physical stability, groundwater seepage control, and faunal changes associated with an AquaBlok<sup>&reg;</sup> sediment cap. Remediation: The Journal of Environmental Cleanup Costs, Technologies and Techniques, 18(4), pp.63-70.  [https://doi.org/10.1002/rem.20183 DOI: 10.1002/rem.20183]</ref>.
 
−
 
 
−
Sediment caps become colonized by microorganisms from the sediments and surface water and potentially become a zone of pollutant biotransformation over time. Aerobic degradation occurs only near the solids-water interface in which benthic organisms are active and thus there might still be significant benthic organism exposure to contaminants. Biotransformation in the anaerobic zone of a cap, which typically extends well beyond the zone of benthic activity, could significantly reduce the risk of pollutant exposure but successful caps encouraging deep degradation processes have not been demonstrated beyond the laboratory.  The addition of materials such as nutrients and oxygen releasing compounds for enhancing the attenuation of contaminants through biodegradation has also been assessed but not applied in the field.  Short term improvements in biodegradation rates can be achieved through tailoring of conditions or addition of nutrients but long term efficacy has not been demonstrated<ref name="Pagnozzi2020">Pagnozzi, G., Carroll, S., Reible, D.D. and Millerick, K., 2020. Biological Natural Attenuation and Contaminant Oxidation in Sediment Caps: Recent Advances and Future Opportunities. Current Pollution Reports, pp.1-14.  [https://doi.org/10.1007/s40726-020-00153-5 DOI: 10.1007/s40726-020-00153-5]</ref>. 
 
−
[[File: SedCapFig2.png | thumb |600px|Figure 2. A conceptualization of a cap with accompanying habitat layer]]
 
−
 
 
−
==Cap Design and Materials for Habitat Restoration==
 
−
In addition to providing chemical isolation and containment, a cap can also be used to provide improvements for organisms by enhancing the habitat characteristics of the bottom substrate<ref name="Yozzo2004">Yozzo, D.J., Wilber, P. and Will, R.J., 2004. Beneficial use of dredged material for habitat creation, enhancement, and restoration in New York–New Jersey Harbor. Journal of Environmental Management, 73(1), pp. 39-52.  [https://doi.org/10.1016/j.jenvman.2004.05.008 DOI: 10.1016/j.jenvman.2004.05.008]</ref><ref name="Zhang2016">Zhang, C., Zhu, M.Y., Zeng, G.M., Yu, Z.G., Cui, F., Yang, Z.Z. and Shen, L.Q., 2016. Active capping technology: a new environmental remediation of contaminated sediment. Environmental Science and Pollution Research, 23(5), pp.4370-4386.  [https://doi.org/10.1007/s11356-016-6076-8 DOI: 10.1007/s11356-016-6076-8]</ref><ref name="Vlassopoulos2017"/>.  Often, contaminated sediment environments are degraded for a variety of reasons in addition to the toxic constituents.  One way to overcome this is to provide both a habitat layer and chemical isolation or contaminant capping layer. Figure 2 illustrates just such a design providing a more appropriate habitat enhancing substrate, in this case by incorporation additional organic material, vegetation and debris, which is often used by fish species for protection, into the surface layer. In a high energy environment, it should be recognized that it may not be possible to keep a suitable habitat layer in place during high flow events.  This would be true of suitable habitat that had developed naturally as well as a constructed habitat layer and it is presumed that if such a habitat is the normal condition of the waterbody that it will recover over time between such high flow events.
 
−
 
 
−
==Summary==
 
−
Clean substrate can be placed at the sediment-water interface for the purposes of reducing exposure to and risk from contaminants in the sediments.  The cap can consist of simple materials such as sand designed to physically stabilize contaminated sediments and separate the benthic community from those contaminants or may include other materials designed to sequester contaminants even under adverse conditions including strong groundwater upwelling or highly mobile contaminants.  The surface of a cap may be designed of coarse material such as gravel or cobble to be stable under high flow events or designed to be more appropriate habitat for benthic and aquatic organisms.  As a result of its flexibility, simplicity and low cost relative to its effectiveness, capping is one of the most prevalent remedial technologies for sediments.  
 
  
 
==References==
 
==References==

Latest revision as of 19:39, 30 December 2025

Thermal Conduction Heating for Treatment of PFAS-Impacted Soil

Removal of Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) compounds from impacted soils is challenging due to the modest volatility and varying properties of most PFAS compounds. Thermal treatment technologies have been developed for treatment of semi-volatile compounds in soils such as dioxins, furans, poly-aromatic hydrocarbons and poly-chlorinated biphenyls at temperatures near 325°C. In controlled bench-scale testing, complete removal of targeted PFAS compounds to concentrations below reporting limits of 0.5 µg/kg was demonstrated at temperatures of 400°C[1]. Three field-scale thermal PFAS treatment projects that have been completed in the US include an in-pile treatment demonstration, an in situ vadose zone treatment demonstration and a larger scale treatment demonstration with excavated PFAS-impacted soil in a constructed pile. Based on the results, thermal treatment temperatures of at least 400°C and a holding time of 7-10 days are recommended for reaching local and federal PFAS soil standards. The energy requirement to treat typical wet soil ranges from 300 to 400 kWh per cubic yard, exclusive of heat losses which are scale dependent. Extracted vapors have been treated using condensation and granular activated charcoal filtration, with thermal and catalytic oxidation as another option which is currently being evaluated for field scale applications. Compared to other options such as soil washing, the ability to treat on site and to treat all soil fractions is an advantage.

Related Article(s):

Contributors: Gorm Heron, Emily Crownover, Patrick Joyce, Ramona Iery

Key Resource:

  • Perfluoroalkyl and polyfluoroalkyl substances thermal desorption evaluation[1]

Introduction

Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) have become prominent emerging contaminants in soil and groundwater. Soil source zones have been identified at locations where the chemicals were produced, handled or used. Few effective options exist for treatments that can meet local and federal soil standards. Over the past 30 plus years, thermal remediation technologies have grown from experimental and innovative prospects to mature and accepted solutions deployed effectively at many sites. More than 600 thermal case studies have been summarized by Horst and colleagues[2]. Thermal Conduction Heating (TCH) has been used for higher temperature applications such as removal of 1,4-Dioxane. This article reports recent experience with TCH treatment of PFAS-impacted soil.

Target Temperature and Duration

PFAS behave differently from most other organics subjected to TCH treatment. While the boiling points of individual PFAS fall in the range of 150-400°C, their chemical and physical behavior creates additional challenges. Some PFAS form ionic species in certain pH ranges and salts under other chemical conditions. This intricate behavior and our limited understanding of what this means for our ability to remove the PFAS from soils means that direct testing of thermal treatment options is warranted. Crownover and colleagues[1] subjected PFAS-laden soil to bench-scale heating to temperatures between 200 and 400°C which showed strong reductions of PFAS concentrations at 350°C and complete removal of many PFAS compounds at 400°C. The soil concentrations of targeted PFAS were reduced to nearly undetectable levels in this study.

Heating Method

For semi-volatile compounds such as dioxins, furans, poly-chlorinated biphenyls (PCBs) and Poly-Aromatic Hydrocarbons (PAH), thermal conduction heating has evolved as the dominant thermal technology because it is capable of achieving soil temperatures higher than the boiling point of water, which are necessary for complete removal of these organic compounds. Temperatures between 200 and 500°C have been required to achieve the desired reduction in contaminant concentrations[3]. TCH has become a popular technology for PFAS treatment because temperatures in the 400°C range are needed.

The energy source for TCH can be electricity (most commonly used), or fossil fuels (typically gas, diesel or fuel oil). Electrically powered TCH offers the largest flexibility for power input which also can be supplied by renewable and sustainable energy sources.

Energy Usage

Treating PFAS-impacted soil with heat requires energy to first bring the soil and porewater to the boiling point of water, then to evaporate the porewater until the soil is dry, and finally to heat the dry soil up to the target treatment temperature. The energy demand for wet soils falls in the 300-400 kWh/cy range, dependent on porosity and water saturation. Additional energy is consumed as heat is lost to the surroundings and by vapor treatment equipment, yielding a typical usage of 400-600 kWh/cy total for larger soil treatment volumes. Wetter soils and small treatment volumes drive the energy usage towards the higher number, whereas larger soil volumes and dry soil can be treated with less energy.

Vapor Treatment

During the TCH process a significant fraction of the PFAS compounds are volatilized by the heat and then removed from the soil by vacuum extraction. The vapors must be treated and eventually discharged while meeting local and/or federal standards. Two types of vapor treatment have been used in past TCH applications for organics: (1) thermal and catalytic oxidation and (2) condensation followed by granular activated charcoal (GAC) filtration. Due to uncertainties related to thermal destruction of fluorinated compounds and future requirements for treatment temperature and residence time, condensation and GAC filtration have been used in the first three PFAS treatment field demonstrations. It should be noted that PFAS compounds will stick to surfaces and that decontamination of the equipment is important. This could generate additional waste as GAC vessels, pipes and other wetted equipment need careful cleaning with solvents or rinsing agents such as PerfluorAdTM.

PFAS Reactivity and Fate

While evaluating initial soil treatment results, Crownover et al[1] noted the lack of complete data sets when the soils were analyzed for non-targeted compounds or extractable precursors. Attempts to establish the fluorine balance suggest that the final fate of the fluorine in the PFAS is not yet fully understood. Transformations are likely occurring in the heated soil as demonstrated in laboratory experiments with and without calcium hydroxide (Ca(OH)2) amendment[4]. Amendments such as Ca(OH)2 may be useful in reducing the required treatment temperature by catalyzing PFAS degradation. With thousands of PFAS potentially present, the interactions are complex and may never be fully understood. Therefore, successful thermal treatment may require a higher target temperature than for other organics with similar boiling points – simply to provide a buffer against the uncertainty.

Case Studies

Stockpile Treatment, Eielson AFB, Alaska (ESTCP project ER20-5198[5])

Figure 1. TCH treatment of a PFAS-laden stockpile at Eielson AFB, Alaska[5]

Since there has been no approved or widely accepted method for treating soils impacted by PFAS, a common practice has been to excavate PFAS-impacted soil and place it in lined stockpiles. Eielson AFB in Alaska is an example where approximately 50 stockpiles were constructed to temporarily store 150,000 cubic yards of soil. One of the stockpiles containing 134 cubic yards of PFAS-impacted soil was heated to 350-450°C over 90 days (Figure 1). Volatilized PFAS was extracted from the soil using vacuum extraction and treated via condensation and filtration by granular activated charcoal. Under field conditions, PFAS concentration reductions from 230 µg/kg to below 0.5 µg/kg were demonstrated for soils that reached 400°C or higher for 7 days. These soils achieved the Alaska soil standards of 3 µg/kg for PFOS and 1.7 µg/kg for PFOA. Cooler soils near the top of the stockpile had remaining PFOS in the range of 0.5-20 µg/kg with an overall average of 4.1 µg/kg. Sampling of all soils heated to 400°C or higher demonstrated that the soils achieved undetectable levels of targeted PFAS (typical reporting limit was 0.5 µg/kg).

In situ Vadose Zone Treatment, Beale AFB, California (ESTCP project ER20-5250[6])

Figure 2. In situ TCH treatment of a PFAS-rich vadose zone hotspot at Beale AFB, California

A former fire-training area at Beale AFB had PFAS concentrations as high as 1,970 µg/kg in shallow soils. In situ treatment of a PFAS-rich soil was demonstrated using 16 TCH borings installed in the source area to a depth of 18 ft (Figure 2). Soils which reached the target temperatures were reduced to PFAS concentrations below 1 µg/kg. Perched water which entered in one side of the area delayed heating in that area, and soils which were affected had more modest PFAS concentration reductions. As a lesson learned, future in situ TCH treatments will include provisions for minimizing water entering the treated volume[6]. It was demonstrated that with proper water management, even highly impacted soils can be treated to near non-detect concentrations (greater than 99% reduction).

Constructed Pile Treatment, JBER, Alaska (ESTCP Project ER23-8369[7])

Figure 3. Treatment of a 2,000 cubic yard soil pile at JBER, Alaska

In 2024, a stockpile of 2,000 cubic yards of PFAS-impacted soil was thermally treated at Joint Base Elmendorf-Richardson (JBER) in Anchorage, Alaska[7]. This ESTCP project was implemented in partnership with DOD’s Defense Innovation Unit (DIU). Three technology demonstrations were conducted at the site where approximately 6,000 cy of PFAS-impacted soil was treated (TCH, smoldering and kiln-style thermal desorption). Figure 3 shows the fully constructed pile used for the TCH demonstration. In August 2024 the soil temperature for the TCH treatment exceeded 400°C in all monitoring locations. At an energy density of 355 kWh/cy, Alaska Department of Environmental Conservation (ADEC) standards and EPA Residential Regional Screening Levels (RSLs) for PFAS in soil were achieved. At JBER, all 30 post-treatment soil samples were near or below detection limits for all targeted PFAS compounds using EPA Method 1633. The composite of all 30 soil samples was below all detection limits for EPA Method 1633. Detection limits ranged from 0.0052 µg/kg to 0.19 µg/kg.

Advantages and Disadvantages

Thermal treatment of PFAS in soils is energy intensive, and the cost of that energy may be prohibitive for some clients. Also, while it often is the least costly option for complete PFAS removal when compared to excavation followed by offsite disposal or destruction, heating soil to treatment temperatures on site or in situ typically takes longer than excavation. Major advantages include:

  • On site or in situ treatment eliminates the need to transport and dispose of the contaminated soil
  • Site liabilities are removed once and for all
  • Treatment costs are competitive with excavation, transportation and off-site treatment or disposal.

Recommendations

Recent research suggests:

  • Successful thermal treatment of PFAS may require a higher target temperature than for other organics with similar boiling points
  • Prevention of influx of water into treatment zone may be necessary.

Future studies should examine the potential for enhanced degradation during the thermal process by using soil amendments and/or manipulation of the local geochemistry to reduce the required treatment temperatures and therefore also reduce energy demand.

References

  1. ^ 1.0 1.1 1.2 1.3 Crownover, E., Oberle, D., Heron, G., Kluger, M., 2019. Perfluoroalkyl and polyfluoroalkyl substances thermal desorption evaluation. Remediation Journal, 29(4), pp. 77-81. doi: 10.1002/rem.21623
  2. ^ Horst, J., Munholland, J., Hegele, P., Klemmer, M., Gattenby, J., 2021. In Situ Thermal Remediation for Source Areas: Technology Advances and a Review of the Market From 1988–2020. Groundwater Monitoring & Remediation, 41(1), p. 17. doi: 10.1111/gwmr.12424  Open Access Manuscript
  3. ^ Stegemeier, G.L., Vinegar, H.J., 2001. Thermal Conduction Heating for In-Situ Thermal Desorption of Soils. Ch. 4.6, pp. 1-37. In: Chang H. Oh (ed.), Hazardous and Radioactive Waste Treatment Technologies Handbook, CRC Press, Boca Raton, FL. ISBN 9780849395864 Open Access Article
  4. ^ Koster van Groos, P.G., 2021. Small-Scale Thermal Treatment of Investigation-Derived Wastes Containing PFAS. Strategic Environmental Research and Development Program (SERDP) - Environmental Security Technology Certification Program (ESTCP), Project ER18-1556 Website, Final Report.pdf
  5. ^ 5.0 5.1 Crownover, E., Heron, G., Pennell, K., Ramsey, B., Rickabaugh, T., Stallings, P., Stauch, L., Woodcock, M., 2023. Ex Situ Thermal Treatment of PFAS-Impacted Soils, Final Report. Eielson Air Force Base, Alaska. Strategic Environmental Research and Development Program (SERDP) - Environmental Security Technology Certification Program (ESTCP), Project ER20-5198 Website
  6. ^ 6.0 6.1 Iery, R. 2024. In Situ Thermal Treatment of PFAS in the Vadose Zone. Strategic Environmental Research and Development Program (SERDP) - Environmental Security Technology Certification Program (ESTCP), Project ER20-5250 Website. Fact Sheet.pdf
  7. ^ 7.0 7.1 Crownover, E., Heron, G., 2024. PFAS Treatment in Soil Using Thermal Conduction Heating. Defense Innovation Unit (DIU) and Strategic Environmental Research and Development Program (SERDP) - Environmental Security Technology Certification Program (ESTCP), Project ER23-8369 Website

See Also

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