The generation of excess soil and/or water during environmental investigations at contaminated sites is inevitable. Although each jurisdiction in Canada provides policies and regulations for waste disposal, there is an absence of federal and provincial regulatory frameworks for the disposal of waste containing PFAS. Despite significant global attention for PFAS as persistent organic pollutants, these contaminants have not been categorized as hazardous materials in Canada as of yet, and subsequently they are not treated as such.

In the absence of regulations for PFAS solid waste, some waste generators may choose incineration (as a destructive approach) and some may prefer on-site encapsulation in an engineered facility (with or without stabilization/solidification). Incineration is a cost prohibitive method, particularly for large volumes of waste. Stabilization/solidification is a more cost-effective approach than incineration, but the cost of purchasing the binding agent and building an engineered soil treatment facility is still considerable.

Currently, transferring excess soil or other sources of solid waste containing PFAS, including exhausted granular activated carbon generated by water treatment systems, to landfills is the preferred option for the majority of federal custodians, as it is the least expensive approach to manage PFAS solid waste.

Waste facility acceptance of solid waste containing PFAS is a commercial decision, but lack of knowledge about the fate and transport of PFAS in landfills as well as the absence of an environmental regulatory approval process, may cause potential environmental liability for waste generators if the leachate is reused or released without an appropriate PFAS analysis.

It is crucial that waste generators determine the types and concentrations of PFAS in the waste to understand the potential risk of PFAS in leachate which may pose risks to human health and environmental receptors of concern. Current regulations across the globe imply that it is the waste generators’ responsibilities to sufficiently characterize the PFAS waste, to reflect the nature of the waste and the associated risk to the waste receiver.

The main objective of this presentation is to summarize current understanding of PFAS fate and transformation in Canadian landfills and review available regulations in other jurisdictions internationally. This presentation will summarize recommended considerations (in a few other countries) for PFAS solid waste owners, prior to transporting the PFAS wastes to landfills. In the absence of PFAS disposal regulations, it is recommended to evaluate conditions of landfills, where receiving the PFAS solid waste, such as landfill siting and lining design, landfill operation, and leachate management and monitoring systems. Details of each condition will be discussed and examples from Australia and United States’ regulations will be deliberated.

Matt Pourabadehei, SNC Lavalin Environment and Geosciences
Matt Pourabadehei is an environmental engineer with over nine years of experience in the assessment and remediation of contaminated sites. His area of expertise is in phased environmental site assessments, remedial option analysis (contaminated soil and groundwater), and remediation of PFAS-impacted soil/sediment. Matt also has international experience in hydraulic/hydrology, sediment control and surface water quality management. He is a technical expert in PFAS projects and has been involved in various federal projects across the country (ON, BC, NT).

Poly- and perfluoroalkyl substances (PFAS) are a group of organo-fluorine compounds, which have received significant attention due to their extreme resistance to biotic and abiotic degradation, potential for bioaccumulation, and toxic properties. Due to the health risk of PFAS at concentrations in the parts per trillion (ppt) range in water and parts per billion (ppb) range in solid matrices, destructive approaches in remedial options for PFAS-contaminated sites are becoming more attractive. Amongst a few destructive approaches available for remediation of PFAS-impacted materials, thermal treatment techniques are more studied and developed.

The focus of this review is on perfluoroalkyl substances, in particular perfluoroalkyl acids (PFAA), and their thermal desorption mechanism from solid matrices (e.g., soil, sediment, wastewater sludge and exhausted granular activated carbon). The main objectives of this review are: i) to highlight the current understanding of thermal treatment capabilities to desorb certain regulated PFAA compounds from solid phase; and, ii) shed light on less understood mineralization mechanism of residual organo-fluorine compounds in fugitive gases generated during the thermal treatment process.

As published in the scientific literature, thermal desorption and mineralization of certain short chained and long chained PFAA have been recently investigated. Temperature and retention time are the main operational parameters that can drastically affect the desorption and mineralization processes. These parameters could also potentially affect the transport mechanisms of certain PFAA compounds from solid phase to gas phase in the contaminated material under treatment.

Although the minimum required temperature for desorption of certain PFAA compounds from solid phase has been documented recently, a range of feasible and cost-effective retention times for thermal treatment of solid impacted media is still not well understood. The correlation between the PFAA carbon chain length and their volatilization rate is also not well documented. A few studies implied that, in general, long-chained PFAA are more reluctant to desorb from solid media matrix compared to short-chained PFAA.

Despite a wide range of research on the minimum temperature to initiate the desorption process for certain PFAA compounds with different results, the majority of the scientists agree that perfluorooctane sulfonate/sulfonic acids (PFOS) and perfluoro-octanoate/octanoic acids (PFOA) can be desorbed from a solid matrix when they are exposed to a minimum of 350ºC - 400ºC for a sufficient retention time.

Although PFAA removal from solid media can be up to 99.9% during a thermal treatment with temperature ranging from 400ºC to 950ºC, results of all bench-scale and pilot test studies concluded that desorbed PFAA are not fully mineralized in the gas phase. A few studies demonstrated that residual organo-fluorine compounds, generated during a high temperature thermal treatment, are present in fugitive emissions and that they will only be mineralized if they are exposed to >1,000ºC in a thermal oxidizer. Therefore, fate and transport of volatile PFAA in gas phase generated during a thermal treatment process needs additional investigations to be better understood.

Mature water treatment techniques for removing PFAS currently use adsorption media such as activated carbon and ion-exchange resins. The operational challenge with using sorption methods lies in the media’s ability to effectively capture the target contaminant(s), all while limiting the frequency of media replacement or regeneration. This challenge is compounded by the complexity of a mixed contamination related to petroleum hydrocarbons, in addition to PFAS, which activated carbon and resin do not necessarily treat. A treatment train must be used to remove PFAS and other contaminants that are present.

For most PFAS-contaminated sites, high levels of soil contamination are often observed and originate from the mode of contamination, as there were FPAS losses on the surface during emergency response team practices for fire extinguishing exercises that use fire fighting foams, a major source of FPAS in the environment. In a comprehensive intervention approach, soil treatment must be considered at the same time as surface and groundwater treatment to reduce the environmental liability of an impacted site.

The project undertaken in fall 2019 began by comparing the performance of the various media available on the market to better understand the physical-chemical phenomena, the levels of PFAS removal and saturation. This exercise helped in selecting the best performing media. This was done using contaminated groundwater and soil from a Canadian military base.

The project then looked at where improvements could be made to increase overall treatment efficiency by optimizing the treatment carbon and resin provide through treatment sequences. Methods combining electrochemistry, liquid/liquid phase transfer, and petroleum hydrocarbon adsorption were therefore tested.

Soil treatment tests were conducted using washing methods. In conjunction with the overall method, the washing water was treated using the water treatment train that was developed during the project. This way, it is possible to treat ex situ soil on location and then reuse it as backfill material. The water treatment system treats both surface and groundwater, as well as soil-washing water.

The project was developed by considering the current regulatory situation in Canada. However, given that existing guide values need to be reviewed, the performance objectives of the tested solutions have been to exceed the current values so that the technological solution that is developed can meet future requirements. The projects continues in the winter and spring of 2020 in order to obtain water and soil treatment solution that is ready for field testing in summer 2020.

Stéphane Venne, Expertise Manager, Research, Development and Engineering Department, Sanexen Environmental Services Inc.
Stéphane Venne has been an expertise manager in the Research, Development and Engineering Department at Sanexen Environmental Services Inc. since April 2019. He graduated with a degree in chemical engineering from Laurentian University and is currently completing his master’s degree in environmental engineering at Carleton University and Polytechnique Montréal, for which he was received several grants. He is also a member of Professional Engineers Ontario as an engineering intern.

Stéphane has considerable knowledge of membrane filtration and advanced oxidation techniques. At Sanexen, he is currently focusing on developing robust and effective treatments chains to address soil and water contaminated with poly- and perfluoroalkyl substances and emerging contaminants.