Identifying the importance of landfills in sequestering PFAS
Submitted by Tetra Tech
Arie Kremen is a civil and environmental engineer with more than 25 years of experience in solid waste engineering and water resources, with an expertise in leachate management and disposal. His academic background is in beneficial reuse of reclaimed wastewater, including biological nutrient recovery. He has worked around the world and in the United States on wastewater and leachate treatment, landfill design and construction, and landfill remediation and closure projects.
Arie is the vice-chair of the Solid Waste Association of North America (SWANA) technical committee on landfill liquids, where he is leading the organization’s effort in building a per- and polyfluoroalkyl substances (PFAS) wiki for the solid waste industry. He also is conducting research to develop a mass balance for estimating the net impact of landfilling on PFAS. As part of his research, Arie is leading a pilot study at a large Michigan landfill to evaluate whether an existing activated carbon system can provide PFAS removal to meet upcoming state regulations. He also is evaluating a groundwater contamination plume for PFAS, emerging contaminants, and 1,4-dioxane at a large New Jersey landfill and assessing if it originates from a closed landfill or other known contaminated sites in the vicinity.
What is PFAS and how is the solid waste industry affected by it?
PFAS are a family of about 4,000 synthetic compounds, developed in the 1940s, and used for surface treatments of clothing, furniture, packaging materials, and in firefighting foams. PFAS are organic compounds with multiple fluorine atoms attached to an alkyl chain, which gives them resilience and desirable surface properties such as heat and stain resistance, water repellence, and chemical resistance. As PFAS-treated products are discarded, PFAS enter the solid waste stream. PFAS-containing products are also disposed of with sanitary and industrial wastewater.
Due to their potential impacts to human health, PFAS are under scrutiny by the public, regulators, and researchers. The principal focus is the effect on groundwater and potable water. Solid waste professionals and practitioners are developing tools and quantifying PFAS content in waste and by-products in coordination with stakeholders and regulators to gauge if and how developing regulations will affect solid waste concerns.
What role does Tetra Tech play with the PFAS issue?
Tetra Tech Solid Waste Solutions practice closely collaborates across the company’s operations involved with PFAS in environmental media. For example, my team works with those that focus on remediation and wastewater, which are also dealing with PFAS in other environmental media.
As projects progress from investigation to design, other teams within Tetra Tech become involved with specialized experience, providing permitting support, and GIS and certified quality auditor services. For example, we are currently investigating PFAS and other emerging contaminants possibly emanating from an unlined landfill. The landfill is contiguous with a lined landfill for which we have designed, permitted, and are constructing a major landfill expansion.
How do landfills interact with PFAS compounds?
Solid waste facilities are not generators of PFAS; rather they landfill wastes, some of which contain PFAS. Some of the PFAS are becoming mobile and can leave the landfill through leachate, with landfill gas, or surface runoff. Leachate is created when rain percolates through the wastebody and then dislodges dissolved and suspended materials. Modern landfills employ baseliner containment and environmental controls to reduce the number of contaminants—including PFAS—from escaping, but PFAS can leach from older, unlined landfills into the subsurface and reach groundwater.
Overall, research indicates that landfills retain more PFAS than they are releasing. Building on my research experience on reactive and multi-phase transport in wastewater irrigated soils, I recently developed a mass balance of PFAS in landfills by aggregating published research results. The data I compiled show that approximately 70 percent of the PFAS discarded in landfills are retained. In other words, they are not released to the environment with leachate, landfill gas, or fugitive emissions.
What are the pathways by which PFAS leaves the landfill?
The overwhelming majority of PFAS leaving the landfill environment are contained within leachate. Leachate may be treated on-site or discharged to the sewer for co-treatment with sanitary wastewater; however, PFAS are resistant to most biological and chemical processes. Some physicochemical treatment processes can remove PFAS, such as through reverse osmosis and adsorption.
While some sanitary, industrial, and leachate wastewaters are low in PFAS, others can contain high concentrations, depending primarily on the contributing industry and consumer habits. PFAS content can vary over time, and it is important to obtain representative, site-specific data rather than relying on published data from other facilities.
PFAS also are being detected in landfill gas (LFG) and have been shown to accumulate on the ground in areas downwind of landfills. While PFAS concentrations in LFG are low, long exposure can result in detectable accumulations. Exposure can be the result of fugitive emissions or from the fact that temperatures and residence times in LFG flares are often insufficient to destroy PFAS. Effective landfill design, LFG collection systems, and adequate cover—especially final covers incorporating synthetic geomembranes—can efficiently control fugitive emissions.
Can landfills help contain PFAS compounds?
My research shows that landfills are an important part of any national solution to the PFAS issue. My forthcoming paper, “MSW Landfills Appear to Be Net Sinks for Per- and Polyfluoroalkyl Substances (PFAS),” uses available data to prepare a mass balance for estimating the net impact of landfilling on PFAS. Results indicate that landfilling has a net positive effect by sequestering PFAS.
Solid waste and wastewater are interconnected through leachate management and landfilling of biosolids produced during wastewater treatment. Besides waste, biosolids—residuals from wastewater treatment—are the second greatest contributors of PFAS to landfills. About 40 percent of the PFAS in landfills originates from biosolids, but only about 20 percent of the biosolids are landfilled. The balance is land-applied—60 percent—and incinerated—20 percent. An increasing number of jurisdictions are limiting land application to reduce the amount of PFAS that can enter the food chain through plant uptake and potable water via groundwater. With relatively few waste incinerators across the nation, increasingly larger amounts of biosolids will be landfilled. Extrapolating from the available data, about half of the additional PFAS may leach from the biosolids, while the other half will remain bound within the landfill. While the mass of PFAS escaping the landfill will increase, landfills will continue to retain more PFAS than being landfilled.
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