Theme: 7. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7f2. In Situ PFAS Soil Treatment Approaches

Formatted Title:

In Situ Stabilization and Solidification for PFAS Remediation in Soils: A Sustainable Solution for Mass Flux Reduction

Background/Objectives:

Per- and polyfluoroalkyl substances (PFAS) are known to accrue in soil beneath fire training areas with historical releases of aqueous film-forming foam (AFFF). Soil bound PFAS are potentially a prolonged source of transport to groundwater flowing below or through impacted soils, as well as surface water transport from run-off. In situ stabilization and solidification (ISS) is an established source zone remediation technology for sequestration/stabilization of numerous contaminants within a range of contaminated material. In comparison to standard excavation and thermal destruction, ISS is a cost-effective and sustainable alternative to reduce PFAS leaching from soil. There are currently multiple commercially available sorbents for soil stabilization, and various sorbents have shown promise in field demonstrations for reducing PFAS mass flux at source zones. Previous field-scale research demonstrated ISS decreased PFAS leachability over a monitoring period of 3 years at an aqueous film forming foam (AFFF) site. While this supports the longevity of reduced PFAS leachability in a specific field case study, investigation into multiple sites is needed to understand the wide-scale application of ISS as a mass flux reduction technique. Arcadis has one of the largest portfolios for PFAS ISS bench-scale and field demonstrations in the US, and thus, leveraged our collective understanding of multiple sites to 1) develop a larger database of bench-scale and field demonstrations for ISS and determine overall mass flux reductions of PFAS at source zones, 2) determine if site specific parameters of field sites influence PFAS mass flux reduction, and 3) detail the cost-effectiveness and sustainability of ISS versus other soil remediation techniques for PFAS.

Approach/Activities:

Baseline characterization results from several site investigations were assembled to evaluate distribution of PFAS in soil and set up the basis for ranges of PFAS/types that were examined for ISS. Two types of commercial sorbents were employed as amendments in bench- and field-scale demonstrations. Leaching tests (LEAF 1314 and 1315) were employed on amended and control soil cores to test longevity and durability of stabilization in soils historically contaminated with PFAS. The different amendments, which were applied at 0.5–4% (w/w), reduced over 96% of PFAS leaching from the soils. Results on the efficacy of select amendments were also examined with respect to site-specific parameters (organic carbon, grain-size, soil type, pH, and co-contaminants) and PFAS mixtures from baseline characterization. Costing and sustainability metrics were compared for ISS versus other soil remediation techniques (excavation/landfilling and thermal destruction).

Results/Lessons Learned:

Commonalities and differences in baseline PFAS concentrations were observed at four field demonstration sites. Each represented an AFFF source zone, however, differences in the mixtures of PFAS were observed. PFAS concentrations from baseline characterization in soil and groundwater ranged from 0.75-14 mg/kg and 2,000-424,010 ng/L, respectively. Bench-scale tests revealed that three of four sites required a 2% amendment addition to achieve PFAS leaching reduction greater than 98% at source zone collected soils. Field performance monitoring for 3 years at site 1 demonstrated sustained reduction of total PFAS mass as measured by LEAF 1315 and post-total oxidizable precursor assay. Differences between commercial amendments will be discussed, as well as correlations to site-specific parameters and PFAS mixtures that influenced overall PFAS mass flux reduction at source zones. Finally, a costing and sustainability analysis for ISS versus other soil remediation techniques for PFAS will be discussed.

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Theresa Olechiw