Per- and polyfluoroalkyl substances (PFAS) are a class of chemical compounds, numbering the thousands, that have gained notoriety in recent years. Containing the strongest bond in organic chemistry, these "forever chemicals" do not degrade and bioaccumulate in animals and humans, a feature that makes them exceptionally toxic. The EPA's latest toxicological research suggests that prolonged exposure to minute quantities of certain PFAS, even less than previously supposed, can lead to detrimental health effects, including cancer. Besides their toxicity, PFAS are distributed worldwide, even in the remotest of places. For instance, PFAS in found in the blood serum in Greenland natives and are suspected to increase breast cancer risk in female Inuit.

Many new major construction projects occur on brownfields impacted by environmental contamination, usually revealed during an Environmental Site Assessment (ESA) as part of a property transaction. Due to PFAS' new arrival on the environmental liability landscape and the lack of federally enforceable standards, very few properties that have had ESAs completed have also assessed potential sources of PFAS. These potential sources are wide-ranging at former industrial properties, with PFAS contained in Class B firefighting foams, paints and coatings, petrochemical products, wood and paper products, consumer home goods, plastics, and many other manufactured materials.

Most PFAS are released via shallow spills or discharges onto the ground, where they can readily migrate through the soils and into groundwater. Once PFAS are in groundwater, they travel along natural flow paths and may contaminate public or private water supply wells. A recent study completed by the Environmental Working Group (EWG) suggests that as many as two-hundred million Americans may be drinking water tainted with PFAS.

The weight of evidence suggests that addressing PFAS groundwater contamination to reduce environmental liability risk will be a feature of many current brownfield redevelopment projects or new construction projects impacted by nearby, currently unknown PFAS sources.

PFAS Remediation Alternatives

Although research is ongoing, there are few options for PFAS treatment in groundwater deployable at the field scale due to the high energy inputs needed to destroy PFAS chemically. And, unlike most other organic contaminants, there is little information to suggest they can be biodegraded.

The technically practical and cost-feasible options for remediation PFAS are limited to chemical sorption. These sorption treatment alternatives for PFAS involve:

• ex situ groundwater treatment: pumping and filtering PFAS out of groundwater above ground;
• in situ groundwater treatment: passively filtering PFAS out of groundwater below ground; and
• in situ soil mixing: amending PFAS-contaminated soil to prevent leaching to groundwater. 

Ex situ treatment, also referred to as pump-and-treat (P&T), is the most common groundwater treatment currently employed for PFAS. It involves pumping water from groundwater extraction wells to the surface and running it through granular activated carbon (GAC) or other sorbent material. It is a reliable approach for impeding groundwater flow and reducing risk to a downstream receptor (i.e., a well or stream). However, the P&T approach generates spent filter material contaminated with PFAS. Due to the EPA's pending regulation of at least two PFAS, spent carbon from these systems will soon be considered hazardous and will likely need to be disposed of at one of the few hazardous waste facilities licensed to handle the waste.

In situ treatment uses a form of colloidal activated carbon (CAC) to passively remove PFAS from groundwater that migrates through a treated zone. The CAC is injected into the subsurface, attaching to the native groundwater aquifer materials and transforming the treatment zone into a purifying filter. By filtering them out of groundwater below the surface, PFAS waste generation is avoided. The approach has been applied to hundreds of organic contaminant sites worldwide and more recently has successfully removed PFAS from groundwater at multiple sites over the last five years.

In situ soil mixing does not treat groundwater directly. Instead, it is a preventative measure used to treat PFAS-impacted soil. This process involves thoroughly mixing unsaturated soil with GAC to increase the soil's sorption capacity and prevent PFAS leaching to groundwater. This approach is usually applied to PFAS source areas and can be combined with the other direct-groundwater-treatment approaches to mitigate PFAS.

In recent months, prominent researchers in the groundwater remediation field have made a case for enhanced Natural Attenuation (NA) as a means to address PFAS. As a process that determines the potential for a PFAS groundwater plume to impact a receptor, there is little doubt that NA will be part of the PFAS-solution toolbox in time, potentially complementing other groundwater treatment methods. 

The extent of PFAS impacts at brownfields and current industrial sites is only just beginning to be realized and it will take years to gain clarity on what needs to be done and where. Construction executives and brownfield developers are advised to be aware of the latest regulations and the current PFAS remediation solutions as needs arise.