Comparing PFAS to other groundwater contaminants: Implications for remediation

Abstract

Established groundwater contaminants such as chlorinated solvents and hydrocarbons have impacted groundwater at hundreds of thousands of sites around the United States and have been responsible for multibillion dollar remediation expenditures. An important question is whether groundwater remediation for the emerging contaminant class comprised of per‐ and polyfluoroalkyl substances (PFAS) will be a smaller, similar, or a larger‐scale problem than the established groundwater contaminants. A two‐pronged approach was used to evaluate this question in this paper. First, nine quantitative scale‐of‐remediation metrics were used to compare PFAS to four established contaminants: chlorinated solvents, benzene, 1,4‐dioxane, and methyl tert‐butyl ether. These metrics reflected the prevalence of the contaminants in the U.S., attenuation potential, remediation difficulty, and research intensity. Second, several key challenges identified with PFAS remediation were evaluated to see similar situations (qualitative analogs) that have been addressed by the remediation field in the past. The results of the analysis show that four out of nine of the evaluated quantitative metrics (production, number of potential sites, detection frequency, required destruction/removal efficiency) indicate that the scale of PFAS groundwater remediation may be smaller compared to the current scale of remediation for conventional groundwater contaminants. One attenuation metric, median plume length, suggests that overall PFAS remediation could pose a greater challenge compared to hydrocarbon sites, but only slightly larger than chlorinated volatile organic compounds sites. The second attenuation metric, hydrophobic sorption, was not definitive regarding the potential scale of PFAS remediation. The final three metrics (regulatory criteria, in‐situ remediation capability, and research intensity) all indicate that PFAS remediation might end up being a larger scale problem than the established contaminants. An assessment of the evolution of groundwater remediation capabilities for established contaminants identified five qualitative analogs for key PFAS groundwater remediation issues: (a) low‐level detection analytical capabilities; (b) methods to assess the risk of complex chemical mixtures; (c) nonaqueous phase dissolution as an analog for partitioning, precursors, and back diffusion at PFAS sites; (d) predictions of long plume lengths for emerging contaminants; and (e) monitored natural attenuation protocols for other non‐degrading groundwater contaminants. Overall the evaluation of these five analogs provided some comfort that, while remediating the potential universe of PFAS sites will be extremely challenging, the groundwater community has relevant past experience that may prove useful. The quantitative metrics and the qualitative analogs suggest a different combination of remediation approaches may be needed to deal with PFAS sites and may include source control, natural attenuation, in‐situ sequestration, containment, and point‐of‐use tr...

Monitored Natural Attenuation to Manage PFAS Impacts to Groundwater: Scientific Basis

“…By comparison, retardation factors in groundwater, where completely saturated aquifer soils rule out contributions from air-water interfacial adsorption, are expected to be lower. For example, Newell et al (2020) estimated PFOS would have a hydrophobiconly retardation factor of 6.0, vs. 2.0 for TCE and 1.3 for benzene (for soils with f oc of 0.01), and the REMChlor-MD model user's manual states that typical retardation factors in groundwater range from 1 to 3 for BTEX compounds (benzene, toluene, ethylbenzene, xylenes) and 2 to 5 for many chlorinated solvents (Farhat et al 2018).…”

“…1. part-per-trillion (ppt) cleanup objectives; 2. the lack of proven destructive in-situ remediation technologies; 3. the number of PFAS in source zones and the limited ability to comprehensively evaluate the PFAS composition; 4. limited information on natural PFAS degradation processes in the subsurface; 5. the mobility and persistence of PFAS in the subsurface; 6. the large size of some PFAS plumes (Simon et al 2019); and 7. the potentially large number of PFAS sites requiring remediation (see three estimates in Newell et al 2020).…”

On Per‐ and Polyfluoroalkyl Substances: Suggested Resources and Considerations for Groundwater Professionals

“…A recent article by Newell et al (2020) moves this discussion forward. The article is also timely given concerns of many in the environmental remediation community that addressing PFAS may be a far greater challenge than for prior contaminants (Simon et al 2019) versus the measured optimism of others (Suthersan et al 2016).…”

“…The article is also timely given concerns of many in the environmental remediation community that addressing PFAS may be a far greater challenge than for prior contaminants (Simon et al 2019) versus the measured optimism of others (Suthersan et al 2016). Newell et al (2020) compares and contrasts PFAS to chlorinated VOCs (including TCE), BTEX (benzene, toluene, ethylbenzene, and xylenes), 1,4‐dioxane, and methyl tert ‐butyl ether (MTBE), all organic contaminants that have affected groundwater and drinking water sources around the world, and resulted in decades of lessons learned from mitigation efforts. The paper considers a range of comparative metrics including total chemical production (i.e., potentially releasable mass to the environment), number of estimated impacted sites, frequency of detection in drinking water aquifers, median plume length, degree of hydrophobic sorption in the aquifer matrix, regulatory criteria stringency, required remediation efficiency, anticipated in situ remediation performance, and intensity of applied research.…”

Addressing the environmental and health impacts of microplastics requires open collaboration between diverse sectors

“…For other “conventional contaminants” (e.g., petroleum hydrocarbons), fate and transport characteristics are well studied [ 68 ]. Due to the diversity of the PFAS class and their unique characteristics (hydrophobic, lipophilic, and surfactant properties), traditional fate and transport models have proven inadequate in modeling their behavior—particularly in groundwater [ 68 , 69 ]. Even less understood are the environmental fate and transport behavior of microplastic particles, in which key determining factors are unique to insoluble particles (relatively less studied than soluble contaminants) and, in some cases, unique to synthetic polymers, such as: formation and emissions of microplastic particles; particle–particle interactions (e.g., aggregation and agglomeration); biological uptake and bioaccumulation; and transport via air and oceanic circulation [ 70 ].…”