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 behaviour 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 reveals many 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, Golder started to characterize and address the PFAS impacts associated with the historical and current firefighting training facilities.
During the site characterization work, Golder 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.
Golder 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 this FTA as the main source of contamination.
Fixing the problem calls for many different skill sets
To address the main sources of PFAS at the site and reduce environmental liability, Golder 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 remediation of the dump site.
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.
Evaluated options to deal with soil and sediment included excavation with off-site disposal, excavation and pre-treatment/stabilization before off-site disposal, 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 granular activated carbon or ion-exchange resins as well as ex-situ on-site treatment with PerfluorAd or RemBind®, and foam fractionation.
Golder 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. Golder also developed recommendations for improving infrastructure and operating procedures at the FTA to minimize future contamination from firefighting training operations.
To address the impacts associated with the dump site, Golder developed technical specifications and design drawings for the excavation of soil and debris along the steep embankment near the river shore. The tender-ready technical specifications were based on the results of soil analytical testing and a detailed site inspection to determine the types of materials located in the dump, the extent of the dump, an approximation of the volume of material located in the dump as well as access and potential health and safety issues.
Golder’s support also included an investigation to identify the approximate age of the materials present in the dump site to support determination of responsibility. The client administered the tender process using Golder’s deliverables and then retained Golder for the supervision and monitoring of the remediation work.
Success factors on this project 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. Following this, the Golder team is now completing the remediation design for the FTA and bench-testing options for the remediation of PFAS-impacted soil and groundwater in the area surrounding the FTA.