As the extensive scope of the PFAS groundwater contamination problem at landfills becomes clearer, solutions to prevent human and environmental exposures to ‘forever chemicals’ will need to be focused on sustainability.
By Maureen Dooley
PFAS (per- and polyfluoroalkyl substances) have been found in groundwater at nearly all landfill sites, with concentrations exceeding state-specific action levels at most of them. Specifically, in Minnesota, PFAS have been detected in groundwater at 97 percent of 101 closed landfills, while 58 percent exceeded drinking water guidance values set by the Minnesota Department of Health.
In New York, more than three-quarters of the landfills tested as part of the state’s Inactive Landfill Initiative Program were contaminated with perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) above the ten parts-per-trillion (ppt) drinking water standard. New York has also followed up with a sampling program to assess whether PFAS contaminants detected in landfills are present in downgradient private or public supply wells, finding 9 percent of the drinking water wells impacted by PFOA and PFOS are above the ten ppt standard.
PFAS has also been detected above the state action levels at most landfills sampled in numerous other states that have instituted sampling programs, including New Hampshire, Michigan, Florida, and California.
These findings make it clear that PFAS-contaminated groundwater is an issue that will need to be confronted at most solid waste disposal facilities, whether these facilities are active or closed or if they have employed leachate controls.
Like other groundwater contamination problems historically facing landfills, engineered solutions for PFAS will mainly be governed by the location where they are applied. At all locations, the massive scale of the PFAS problem demands economically/environmentally sustainable solutions to protect downstream communities and environmental receptors.
In this light, sustainability-focused treatment approaches are reviewed for the three primary locations of a PFAS plume:
1. The source area—comprising raw landfill leachate and highly impacted groundwater
2. The groundwater contaminant plume body—characterized by low contaminant concentrations
3. The drinking water zone—e.g., impacting private or public water wells
Treatment Zone: Source Area (Leachate/High Contaminant Concentrations)
Treatment Goal: Sustainably Reduce Contaminant Mass Loading into Plume, Including PFAS
Leachate, a wastewater complex containing large amounts of organic materials, ammonianitrogen, heavy metals, and other contaminants, including PFAS, is the source of groundwater contamination at most landfills. Native groundwater becomes impacted by leachate migrating away from unlined landfills or escaping through gaps in a lined landfill’s leachate containment/treatment system.
In the source area, the treatment goal is to substantially reduce PFAS and other contaminants feeding a groundwater plume. Reducing contaminant mass at the source to inhibit further plume development is an essential component of groundwater cleanup strategies used across all industries. Emerging approaches that can destroy the extremely stable carbon-fluorine bonds in PFAS while also sustainably addressing the massive non-PFAS contaminant load will likely be favored over other approaches.
PFAS in Leachate
PFAS comprise only a tiny fraction of the total contaminant load in landfill leachate. A typical leachate sample may contain PFAS concentrations in the single parts per billion compared to total chemical loads in the hundreds to thousands of parts per million range. This difference roughly compares to one second passing over a timeframe spanning multiple days to weeks.
Treating leachate for PFAS using traditional methods like pump and treat is often not desirable since sorbent media like granular activated carbon (GAC) or ion exchange resins (IER) used in pump and treat systems are quickly overwhelmed by the other organic contaminants, greatly diminishing PFAS treatment effectiveness. Additionally, the process generates tons of PFAS—laden waste material which must be disposed of or incinerated, creating the potential to recycle the contaminants back into the environment via potential future landfill leachate releases to groundwater or air releases of PFAS caused by incomplete combustion.
Thermal decomposition technologies like Supercritical Water Oxidation (SCWO) or Hydrothermal Alkaline Treatment (HALT) rely on creating extreme temperature/pressure conditions to achieve a supercritical state for water, which occurs at temperatures above 700 degrees Fahrenheit and pressures exceeding 3,000 pounds per square inch. This technology essentially “pressure cooks” the liquid, providing the energy needed to break the highly stable carbon-fluorine chemical bonds in PFAS.
Due to the high energy inputs and associated costs with hydrothermal destruction, an emerging sustainable approach focuses on reducing the waste stream treated by them. A technology known as surface active foam fractionation (SAFF) has recently been deployed at landfills to reduce the volume of PFAS waste material from leachate. The method concentrates PFAS by bubbling air through a series of tanks filled with leachate/contaminated water by pumping. PFAS attach to the air bubbles and rise along with them to the air/water interface near the top of each tank, becoming concentrated at each stage sequentially. The result is a highly concentrated PFAS waste product that can be treated by SCWO, HALT, electro-chemical oxidation, or other energy-intensive approaches more economically than without SAFF treatment.
Treatment Zone: Groundwater Contaminant Plume Body (Low Concentrations)
Treatment Goal: Sustainably Reduce Downgradient PFAS Exposure Risk
PFAS are exceptionally persistent and mobile, forming much more extensive plumes than other groundwater contaminants. Because PFAS plumes are so extensive, they are also highly diffuse. Groundwater samples from these plumes often show PFAS in the parts per trillion range throughout most of a plume’s volume. These characteristics, combined with the low detection limits that laboratories use to identify PFAS, can sometimes make it difficult to find the end of a PFAS plume. There is little mystery as to why these chemicals are found in so many drinking water systems and private wells.
Sustainability, especially when treating the body of a PFAS plume, must be at the forefront of remedial decision-making. Given the vast nature of PFAS plumes, which can often extend for thousands of feet and even miles beyond a landfill facility’s property, the treatment goal in the plume body needs to be tightly focused on preventing downstream PFAS exposures. Doing more, such as restoring a PFAS plume to drinking water standards, is neither practical nor feasible.
Energy-consuming mechanical systems pumping millions of gallons of water aboveground are not sustainable for PFAS plume treatment. Consider that a typical downhole pump in a well 30 feet deep can generate more than 10,000 lbs. of carbon dioxide into the atmosphere each year. Stopping PFAS plume migration would typically require multiple such wells pumping for decades or longer, resulting in huge monetary costs to society and considerable damage to the atmosphere.
Alternatively, plume treatments that take advantage of groundwater’s natural movement to treat contaminants are favored for sustainability and overall effectiveness. The sustainable plume treatment approach creates a passive below ground filtering system that removes PFAS and other contaminants from groundwater. Colloidal Activated Carbon (CAC), a proprietary, ink-like material comprised of blood-cell-sized activated carbon particles and an environmentally safe dispersing agent, is injected directly into the groundwater. CAC coats aquifer materials, forming permeable sorptive barriers that filter out PFAS as groundwater passes through them.
Installed CAC treatments are a fraction of the cost as compared to other PFAS treatment approaches. More importantly, they produce no greenhouse gas emissions or disposal wastes, do not consume energy or generate noise pollution, require minimal infrastructure (i.e., only the performance monitoring wells), and have no post-installation maintenance. CAC treatments have received favorable Green and Sustainable Remediation (GSR) ratings from regulatory agencies in the U.S. and Europe.
CAC permeable barriers are engineered to provide decades of effective PFAS treatment with performance warranty options available for qualifying sites. The PFAS treatment approach is now being used at more than 30 sites globally, with numerous case studies and scientific publications attesting to its effectiveness.
Treatment Zone: Drinking Water
Treatment Goal: Immediately Remove PFAS to Safe Drinking Water Levels
The drinking water zone refers to groundwater within the pumping radius of a private or public supply well. Once PFAS contaminants have entered a water well, the situation changes from risk reduction to emergency response. Sustainability concerns must necessarily take a back seat. If a private well is confirmed to be impacted, state environmental agencies and health departments will typically provide bottled water until a more permanent, point-of-exposure-treatment (POET) system is installed on the private water service or public service is extended to the residence. These should be installed by a professional water treatment specialist familiar with PFAS treatment. Many under-the-sink and water pitcher filter systems have been proven to be ineffective against eliminating PFAS.
If a public water supply well is impacted by PFAS above applicable standards, the water utility’s treatment options are minimal currently. Attaching aboveground PFAS filtering systems to the pumping wells using GAC, IER, or membrane filters (i.e., pump and treat) is the most used approach. Water providers may also assess drilling new water supply wells in clean areas of the aquifer, if feasible. Purchasing clean water from a nearby utility has also been a remedy. Each of these alternatives is associated with millions of dollars in costs which are passed on to the customers. Some U.S. municipalities are suing PFAS manufacturers for damages. Certainly, treating PFAS before these exposures and damages occur is the best practice.
A Sustainable, PFAS-Free Future
The full extent of PFAS in the environment and associated health risks continues to surprise and alarm. With more evidence added daily, PFAS already represents one of the biggest environmental challenges of our day. In time, the international push to remove PFAS from manufacturing will help reduce our exposure to these chemicals.
Meanwhile, landfills are among the many facilities confronted with addressing PFAS contamination in groundwater. Some of these problems will be large and complex, requiring sustainable, low-cost, and effective solutions focused on preventing further environmental and human PFAS exposures downstream.| WA
Maureen Dooley is Vice President – Industrial Sector at REGENESIS®. She can be reached at [email protected].