Enhanced natural attenuation is likely to be the ‘go-to’ remedy in the future of PFAS groundwater treatment. With recent innovations in colloidal carbon suspensions,
remediation practitioners can now modify the aquifer materials directly to sorb PFAS.
By Ryan Moore

Researchers have recently proposed guidelines to remediate PFAS-contaminated groundwater by demonstrating a plume can be controlled and is not a threat to downstream drinking water wells or water bodies. Demonstrating a plume’s ‘natural attenuation’ is an established approach in the environmental remediation industry and is ready for adoption by solid waste facility operators to cost-effectively manage PFAS impacts. However, the recommended approach will need to be augmented by sustainable, enhanced
attenuation remedies in most cases.

Research Now Shows All Waste Disposal Facilities and Most Public Water Supplies are at Risk for PFAS Contaminants
As the EPA draws closer toward regulating PFAS, more landfill sites are likely to discover PFAS impacts in groundwater. Landfill sampling efforts led by several state environmental agencies reveal the following:
• New Hampshire—PFAS groundwater impacts are associated with 92 percent of unlined landfills, and 77 percent sampled exceed the EPA Health Advisory Level.1
Minnesota—97 percent of closed landfills sampled have PFAS-contaminated groundwater, with more than half exceeding the state’s action levels, including one by more than 1,000 times.2
Florida—50 percent of the landfills sampled exceed the state action levels.3
• Michigan—34 percent of the state’s 200 confirmed PFAS sites are waste disposal facilities, with many showing one or more PFAS above target concentrations.4

Depiction of a PlumeStop® permeable reactive barrier removing PFAS from groundwater downgradient of a source zone.
Image Courtesy of REGENESIS®.

PFAS Identified in 60 Percent of Public Water Supply Wells
The prevalence of PFAS found in landfill groundwater coincides with a February 2022 USGS report identifying one or more PFAS in 60 percent of public water supply wells and 20 percent of private wells in Eastern U.S. aquifers.5

Given these statistics, it is obvious to predict many waste disposal facilities will be required to address PFAS contaminated groundwater as Federal regulations are determined. Moreover, the Biden Administration’s focus on environmental justice is expected to pressure many of these facilities located in or near economically disadvantaged
communities to address offsite impacts sooner than later.6 This key driver will be most substantial where there is a threat, real or perceived, of PFAS migrating from a landfill to drinking water wells downstream in these underserved communities.

Destructive PFAS Technologies in Development are Not Suitable for Groundwater
There is strong interest in the solid waste industry to quickly
identify and scale-up methods to literally ‘break the chain ‘(i.e., break the chemical bonds) of these ‘forever chemicals’ and put an end to recycling PFAS back into the environment. A few of these destruction technologies were presented at the 2022 Global Waste Management Symposium, including:
• Electrical plasma reactors that convert water into highly reactive species
• High-energy electron beams that react with water to form free radicals and hydrogen atoms
• Ultrasound units that create cavities in liquids, generating high temperatures and pressures
• Supercritical water oxidation (SCWO) systems where organic materials in water (e.g., PFAS) are transformed into harmless byproducts7

The immediate, pressing need to manage leachate drives the development of these technologies. Sewage treatment plants are now refusing the ‘garbage juice’ since most are not equipped to treat PFAS. However, these technologies are not practical for addressing PFAS in groundwater since they all require high energy inputs to achieve the desired destructive effect. A more energy-efficient, sustainable, and less costly method is needed to manage PFAS in groundwater effectively.

Visual Depiction of PFAS sorption onto CAC.

Monitored Natural Attenuation: An Established Solution for Managing Groundwater Contamination
Natural attenuation refers to physical, chemical, or biological processes that allow contaminants to degrade naturally without active intervention.8 Monitored Natural Attenuation, or MNA, is the method used to demonstrate attenuation is occurring and sufficient exposure risk to hazardous chemicals is avoided. In simple terms, the goal of most MNA remedies is to show, through periodic groundwater monitoring, a contaminant plume in groundwater is stable or shrinking and will not continue to migrate toward a potable well or surface water.

MNA has been used as a ‘passive’ remedy for managing groundwater contaminants for decades, starting with fuel hydrocarbons and then expanding to chlorinated solvents in the 1990s. These contaminant classes naturally biodegrade in the environment to varying degrees. In the 2000s, MNA expanded to contaminants such as metals and radionuclides, which do not biodegrade similar to today’s PFAS class of contaminants.

MNA Adoption for PFAS will Save Billions in Environmental Cleanup Costs
Groundwater remediation experts recently published technical research papers outlining the scientific basis and potential guidelines for managing PFAS contamination via MNA, relying on the precedent set for non-biodegradable inorganics (e.g., metals).9,10 The approach is currently being studied under the Defense Department’s Environmental Security Technology Certification Program (ESTCP Project ER21-5198).11 Managing PFAS via MNA is expected to be openly received given the multitude of challenges for remediating these hard-to-treat contaminants, including their prevalence, low part-per-trillion cleanup levels, and the lack of sustainable methods to
destroy the compounds at the groundwater-remediation scale.

Adopting MNA for PFAS will save billions in remediation costs compared to energy-intensive approaches (e.g., pump and treat) that extract the contaminants from the ground and transfer them to landfills—a process that recycles the PFAS back into the groundwater as the landfill sampling data noted suggest.

MNA was initially met with skepticism upon release of the first guidelines, appearing as a ‘do-nothing’ remedial alternative to some. However, the reality is that MNA has most commonly been used to help define what active remediation must be done and where it should be focused so that natural attenuation mechanisms can achieve plume control with strategic assistance. Many of these focused approaches work with the natural attenuation processes by enhancing them.

Enhanced Natural Attenuation
For decades, groundwater remediation practitioners have used Enhanced Attenuation, defined by the Interstate Technology & Regulatory Council (ITRC) as “the result of applying an enhancement that sustainably manipulates a natural attenuation process, leading to an increased reduction in mass flux of contaminants.”12
Natural attenuation enhancements are necessary when MNA and associated groundwater plume modeling indicate these processes, on their own, will not entirely stop a contaminant plume from impacting a receptor. In these cases, natural attenuation is enhanced by adding substrates to the soil and groundwater that stimulate in situ
contaminant retardation and degradation, often in combination.

Often, attenuation only requires a nudge to tip the scales toward plume stagnation and elimination of environmental risk to down-gradient receptors. Targeted remediation efforts supporting MNA are primarily focused in the source zone or near-source plume areas using permeable reactive barriers (PRBs) to intercept and treat the zones transporting the contaminants (i.e., the mass-flux zones).

Enhancing PFAS Attenuation Using Colloidal Activated Carbon
Currently, PFAS cannot be destroyed biologically within acceptable timescales. Therefore, enhancing attenuation for PFAS can be accomplished by increasing the aquifer’s ability to sorb the chemicals. Since 2014, direct physical enhancement of aquifer materials has been widely demonstrated using a patented form of aqueous colloidal activated carbon (CAC).13 The CAC is applied to the subsurface under low-pressure, aided by a proprietary anti-clumping agent. CAC is composed of micron-scale activated carbon particles that permanently coat the aquifer solids, forming a below-ground purifying filter for organic contaminants like PFAS. CAC treatments create an immense surface area of activated
carbon for sorption of PFAS and have shown to reduce concentrations quickly and consistently below detections in the single part-per-trillion range of most laboratory method detection limits. With a sorption area on the order of 100 acres per pound, an attribute unique to the patented CAC technology is that it operates most efficiently when applied to the low-concentration plumes characteristic of PFAS. A single CAC barrier provides many decades of PFAS sorption capacity, maximizing sustainability and cost-effectiveness. Numerous in-field case studies and customizable performance warranty options are available to support this claim.14,15,16,17,18

Enhanced natural attenuation is likely to be the ‘go-to’ remedy in the future of PFAS groundwater treatment. With recent innovations in colloidal carbon suspensions, remediation practitioners can now modify the aquifer materials directly to sorb PFAS. By sequestering the chemicals in place, downstream PFAS exposure risk is removed without generating more PFAS materials for recycling back into the groundwater.

With the rapidly expanding multitudes of PFAS groundwater plumes now being discovered around the world, including at potentially thousands of waste disposal facilities, this low-cost, effective, and environmentally sustainable approach is specifically engineered and well-positioned to tackle the challenge. | WA

Ryan Moore, CHMM, is a REGENESIS PFAS Program Manager, focused on collaborating with environmental professionals and the industry at large in communicating effective, proven approaches to manage sites where PFAS contaminants exceed regulatory standards. Ryan has managed the use of PlumeStop®, Colloidal Activated Carbon™, available exclusively through REGENESIS, to treat PFAS and other organic pollutants since its inception in 2014. Ryan can be reached at (219) 286-4838 or e-mail [email protected].

1. Doherty AT, Schlosser KEA. Sources of PFAS Impacts to New Hampshire Groundwater. Presented at: Northeast Waste Management Officials’ Association Webinar Series; July 29, 2020; New Hampshire Department of Environmental Services.
2. Nearly 60 closed landfills in 41 counties have PFAS contamination in groundwater that exceeds the state’s health value. Minnesota Pollution Control Agency. Published March 18, 2021. Accessed February 28, 2022. www.pca.state.mn.us/news/nearly-60-closed-landfills-pfas-contamination-groundwater-exceeds-state-health-values
3. Waste Site Cleanup State Funded PFAS Sampling Efforts | Florida Department of Environmental Protection. Accessed March 7, 2022. https://floridadep.gov/waste/waste-cleanup/content/waste-site-cleanup-state-funded-pfas-sampling-efforts
4. Michigan PFAS Sites. Accessed March 1, 2022. https://gis-egle.hub.arcgis.com/datasets/michigan-pfas-sites-1/explore?location=44.578950,-86.388492,7.00
5. McMahon PB, Tokranov AK, Bexfield LM, et al. Perfluoroalkyl and Polyfluoroalkyl Substances in Groundwater Used as a Source of Drinking Water in the Eastern United States. Environ Sci Technol. 2022;56(4):2279-2288. doi:10.1021/acs.est.1c04795
6. US EPA O. ICYMI: On his Journey to Justice, EPA Administrator Michael S. Regan Toured Historically Marginalized Communities in the American South, Highlighted Benefits of Bipartisan Infrastructure Law. Published November 22, 2021. Accessed March 7, 2022. www.epa.gov/newsreleases/icymi-his-journey-justice-epa-administrator-michael-s-regan-toured-historically
7. Brown T PE. PFAS Treatment through Destruction and a Case Study on High Energy Electron Beam Treatment. Presented at: Global Waste Management Symposium; February 2022. Accessed March 3, 2022. www.dropbox.com/sh/fpnq9v0yqswlnsz/AAA6c7vyN95vrOhmS5J0Fvp7a/Session%202_Track%20C?dl=0&preview=Brown_PFAS+Treatment+Through+Destruction+and+a+Case+Study+on+High+Energy+Electron+Beam+Treatment.pdf&subfolder_nav_tracking=1
8. U.S. EPA. Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites, EPA/9200.4-17P. Published online 1999:41.
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11. Adamson DT. Developing a Framework for Monitored Natural Attenuation at PFAS Sites ER21-5198. SERDP ESTCP Environmental Research Programs. Accessed December 15, 2021. www.serdp-estcp.org/Program-Areas/Environmental-Restoration/ER21-5198/ER21-5198
12. ITRC (Interstate Technology & Regulatory Council). Enhanced Attenuation: Chlorinated Organics. EACO-1. Washington, D.C.: Interstate Technology & Regulatory Council, Enhanced Attenuation: Chlorinated Organics Team. www.itrcweb.org. Published online 2008.
13. Patents. REGENESIS Remediation Solutions. Accessed March 7, 2022. https://regenesis.com/en/patents/
14. Moore R. Treating PFAS at Camp Grayling. The Military Engineer. 2022;(737):52-53.
15.McGregor R. In Situ treatment of PFAS-impacted groundwater using colloidal activated Carbon. Remediation Journal. 2018;28(3):33-41. doi:10.1002/rem.21558
16. McGregor R. Six pilot-scale studies evaluating the in situ treatment of PFAS in groundwater. Remediation Journal. 2020;30(3):39-50. doi:https://doi.org/10.1002/rem.21653
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18. PlumeShield – Guaranteed Long-Term Elimination of PFAS Risk. REGENESIS Remediation Solutions. Accessed March 7, 2022. https://regenesis.com/fr/plumeshield-pfas-risk-warranty/