When cleaning up an environmental problem on a piece of property, it is important to establish the extent of liability, so that the owners can plan the work and set a budget. Often, this is done through determining the scope of the problem, choosing the best remediation methods, and establishing how to know when the work has achieved its aims.
Projects of this type are particularly challenging when it comes to soil, sediment and water impacted by Per- and Polyfluoroalkyl Substances, collectively known as PFAS. A major contributor to this challenge is that scientific information on the behavior and toxicology of PFAS is still progressing even after over a half century of use. Consequently, the treatment of these compounds continues to evolve as well.
One common source for PFAS has been their use in firefighting foams. This means that PFAS impacts are found at many airports around the world, where safety measures have called for frequent practice by firefighting crews – and the result has often been that PFAS-containing materials have impacted nearby soil, water and other environmental media.
Investigation identifies main sources of PFAS impacts
This was the case at an international airport in North America where PFAS were used in multiple areas of the site over the last 50 years. In 2009, WSP* started to characterize and address the PFAS impacts associated with the historical and current firefighting training facilities.
During the site characterization work, WSP* found a complex hydrogeologic setting, with two water bearing units. One was a perched aquifer – a water-bearing unit lying above the water table above a low-permeability layer, or aquitard. This perched aquifer overlies an unconfined aquifer that receives recharge water from areas located upgradient of the site and from the upper water-bearing unit via slow percolation through an aquitard.
WSP* found that PFAS were being carried overland and transported via groundwater towards a river and one of its tributaries. The team also found a former dump site downgradient of the firefighting training area (FTA), on an embankment along the river shore. It contained drums, pails, equipment, and other material for storage of liquid foam concentrate, oil, and lubricants. The waste material extended down about three metres (12 feet) below surface. Using a multiple lines of evidence approach, the investigations identified the main sources of contamination and this helped focusing on the development of the most effective management strategy.
Fixing the problem calls for many different skill sets
To address the main source of PFAS at the site and reduce environmental liability, WSP* carried out a Remedial Investigation/Feasibility Study for PFAS impacts at the FTA and surrounding area, developed technical specifications and construction drawings, and supervised construction for the decommissioning the remediation of the dump site and FTA.
The remediation feasibility study included development, screening, and detailed evaluation of conventional as well as innovative remedial options and assessment of their applicability based on site-specific settings, regulatory framework, and site management objectives.
WSP* estimated costs for each option by taking into consideration all the main work phases including design, permitting and contract administrations, site preparation, execution, site restoration, short- and long-term operation/maintenance, and post-remediation monitoring.
To address the impacts associated with the dump site and for the decommissioning of the FTA, WSP* developed technical specifications and design drawings. The tender-ready technical specifications were based on the results of soil, sediment and water analytical testing and a detailed site inspection to determine the volume of impacted materials in the FTA as well as types and quantities of materials located in the dump site along with potential health and safety issues. WSP*’s mandate also included an investigation to identify the approximate age of the materials present in the dump site to assist with the determination of responsibility. The client administered the tender process using WSP*’s deliverables and then retained WSP* for the supervision and monitoring of the remediation work.
Success factors on the remediation included technical quality and innovation to identify the most effective and sustainable options for addressing PFAS impacts as well as proactively identifying key technical requirements for different site management scenarios.
Addressing the PFAS impacts downgradient
Following the remediation of the PFAS source areas, the WSP* team completed bench- and pilot-testing of the most promising technologies for addressing PFAS in both soil and water downgradient of the FTA to minimize PFAS transport towards water bodies.
Evaluated options to deal with soil and sediment included excavation with off-site disposal, stabilization, soil washing, thermal desorption, ball milling and capping. Options to deal with the PFAS impacted water included in-situ options such as the installation of a permeable reactive barrier or injections of colloidal activated carbon, ex-situ treatment with electro-oxidation, granular activated carbon or ion-exchange resins as well as ex-situ on-site treatment with foam fractionation. To end the PFAS cycle in the environment, specific focus was given to destructive technologies such as ball milling for soil and electro-oxidation for water.
A numerical groundwater flow and PFAS transport model was developed to support the identification of the most promising remedial options and assessment of the treatment schedule.
WSP* is currently monitoring the results of the pilot tests and will use them as input to the full-scale remediation design for the areas of the site downgradient of the FTA.
* This work was performed by WSP* professionals who joined WSP in an acquisition completed in 2021.
