Per- and poly-fluoroalkyl substances (PFAS) are highly persistent anthropogenic compounds that have been used extensively in consumer products, manufacturing processes and in aqueous film forming foams (AFFF). With over 3,000 different chemicals within the class, their presence in the environment is ubiquitous throughout all environmental media, particularly in the cases of perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and perfluorohexane sulfonate (PFHxS). The regulatory status of PFAS is rapidly developing across the globe, with Australia leading the way in remediation and risk assessment technologies. Human health and ecological risk assessments for PFAS present new challenges due to the unique physicochemical properties of these compounds. Our relative uncertainty regarding the toxicity of PFAS has resulted in low (i.e., conservative) screening values that, in turn, have the potential to result in anxiety in communities surrounding sites contaminated by PFAS. Therefore, there are many considerations and lessons learned from projects underway in Australia that can help to guide upcoming projects in Canada and the U.S. as the focus on PFAS-contaminated sites expands.

PFAS science is not yet where it needs to be for engineers and scientists to provide answers/solutions to stakeholders with a high level of certainty. Decisions tend to be therefore based on a more precautionary approach. This can be both frustrating and stressful for all parties. With new information becoming available as research and government agencies continue to study and understand PFAS, some of it may help, while some of it may further complicate what has been said or done; especially when non-federal stakeholders propose trigger values with limited scientific background to justify them.

The current limitations significantly impact how to best communicate risks and proposed next steps to a broad audience while maintaining trust and credibility. For example, the decision for on-going sampling is based on the risk tolerance of the client, possibly influenced by other stakeholders and media perception. For well-researched chemicals, detectable concentrations below applicable or relevant and appropriate requirements (ARARs) would not identify the need for on-going sampling; however, given the limited scientific information available for PFAS, the presence of detectable concentrations can trigger continued sampling and delineation, even below ARARs.

This presentation will highlight lessons-learned from real projects challenges that have included: (1) complex sampling; (2) evolving analytical techniques; (3) development of new ARARs; (4) the identification of new off-site sources of PFAS; (5) communicating the new PFAS information to stakeholders, including residents and government officials; and, (6) responding to client requests (socio/political/scientific).

In summer 2014, Public Services and Procurement Canada (PSPC) successfully completed the demolition of the ten-storey Sir John Carling Building and incorporated a sustainable waste management approach by crushing and using the concrete from the former structure for fill at the site. The next spring, a white residue was observed flowing from a storm sewer that originated from the site and discharged into Dow’s Lake, part of the Rideau Canal System, a UNESCO Heritage site located in Ottawa, Ontario. Environment and Climate Change Canada, as well as the Ministry of the Environment and Climate Change (Ontario), became involved based on the mysterious discharge to fish bearing waters. PSPC responded quickly and assessed the quality of the storm water and found elevated levels of phenols in the discharge. Services were retained to complete a forensic phenol assessment to identify the potential phenol source(s), develop a conceptual site model and identify potential remedial/risk management options.

This presentation will focus on the approach used to identify the source of the phenols, the remediation/risk management options considered and ultimately selected. We will also present the lessons learned during this project from planning the building demolition, contractor oversight, environmental assessment programs and limitation with various analytical methods inherent to a forensics assessment of phenolic compounds.

1,4-Dixoane is a common co-contaminant with chlorinated solvents, but is not readily remediated via similar treatment approaches (e.g., sorption, reductive dechlorination). However, 1,4-Dioxane can be co-metabolically biodegraded in the presence of alkane gases and oxygen. At Vandenberg Air Force Base in California, historical use of chlorinated solvents resulted in 1,4-dioxane in groundwater. Previously, in-situ propane biosparging was implemented and resulted in short-term 1,4-dioxane concentration reductions of up to 99% (as published by others). This work builds on the prior field demonstration to confirm biodegradation as the mechanism for 1,4-dioxane concentration decreases via stable isotope probing (SIP). SIP includes addition of a 13C-enriched compound into the test system to act as a carbon-atom tracer to track the biotransformation of 1,4-dioxane.

This second propane biosparge field demonstration was initiated in December 2015. Operation of the system included sparging a mixture of air and propane (20% of the LEL) at up to 5 standard cubic feet per minute into one sparge point, for 30 minutes every four hours. Bioaugmentation with a propanotrophic culture was conducted, alongside nutrient addition of diammonium phosphate. SIP included use of Bio-Trap® samplers “baited” with isotopically enriched 1,4-dioxane.

After two months of operation, 1,4-dioxane concentrations decreased approximately 45 to 83 percent at monitoring locations in the test area. The SIP results confirmed the biodegradation mechanism associated with 1,4-dioxane groundwater concentration decreases. The co-metabolic biotransformation of 13C-enriched 1,4-dioxane is expected to result in generation of carbon dioxide which was measured as 13C-enriched dissolved inorganic carbon. Additionally, evaluation of microbial biomass indicated incorporation of 13C into the cellular phospholipids. Because significant carbon uptake into microbial biomass is not commonly associated with co-metabolism, the 13C-enriched biomass values observed here may be attributed to uptake of the mineralization intermediates or the carbon dioxide end product, rather than the 1,4-dioxane directly. The success of the propane biosparge demonstrations and confirmation of the biodegradation mechanism via SIP has led to the full-scale implementation planning of a propane biosparge treatment system at Vandenberg Air Force Base. This full-scale system is expected to be among the first of its kind.

Use of aqueous film forming foam (AFFF) in the military, aviation, oil and gas, and a myriad of other industries from the 1970’s until recently has resulted in impacts to soil and groundwater in many locations. AFFF contains per- and polyfluoroalkyl substances (PFAS), which have been identified as compounds of interest and are considered emerging contaminants. Recent studies indicate that these compounds are relatively common in association not only with fire training areas, as would be expected, but in proximity to aviation hangars, municipal fire stations, wastewater treatment plants, landfills, and aircraft or rail crash sites.

The widespread usage and occurrence also has the potential to impact Brownfields and province-led clean-up projects. Increasing regulatory scrutiny and public awareness has resulted in numerous jurisdictions issuing screening levels, guidance levels, or in rare cases, mandated clean-up standards in soil or groundwater. In Canada, there are human-health based screening levels for PFOA (0.85 mg/Kg) and PFOS (2.1 mg/Kg) which are similar to values in some bordering states such as Alaska, New Hampshire, and Minnesota. Given risk-based guidance values established for water, states such as Michigan and Alaska have adopted soil-screening levels for groundwater protection which are orders of magnitude lower (0.0017 to 0.075 mg/Kg). As such, as the regulations continue to be established, groundwater protection could drive soil values in Canada even lower.

Some of these groundwater-protection values are extremely low and result in almost universal exceedances where samples are collected at facilities where AFFF was used. Because these compounds have only recently been discovered, the overall understanding of their nature and extent is limited, especially when compared to our knowledge of the behaviour of petroleum constituents, chlorinated solvents and metals. However, the state of knowledge is growing as more sites are investigated.

Construction projects frequently involve soil removals, demolition of fire stations, hangars, and associated buildings where AFFF was used, runway extension and replacement, and demolition or construction of wastewater treatment facilities. These projects involve large-scale earthworks and often some form of construction dewatering to enable construction of foundations and drain systems below the static water table. Additionally, construction projects often include stormwater management addressing large quantities of surface water. Handling these potentially-impacted media under emerging regulatory programs is an increasing challenge.

Given the likelihood of encountering PFAS-impacted soil, surface water or groundwater, having a complete understanding of the conceptual site model (CSM) is critical in the early planning stages of construction projects. The CSM must consider the storage, usage and release of AFFF through time, as well as the fate and transport characteristics of PFAS. Considering the CSM in pre-design and planning activities could allow project teams to incorporate design elements which could reduce treatment or disposal of impacted materials. Recent literature indicates PFAS presence in concrete from fire training areas and fire station building materials, requiring careful scrutiny of disposal practices for construction debris.

This presentation will discuss PFAS sources, CSM issues affecting mobility and occurrence, and disposal, treatment, and management options for this emerging group of contaminants.