RAAF Townsville PFAS remediation: comprehensive soil and groundwater cleanup
At a glance
GHD successfully led a $10.6M PFAS remediation project at the former fire training area (FFTA) at RAAF Base Townsville, Queensland. This project tackled complex environmental challenges at a live Defence airport, like scheduling the remediation works around the wet season, to minimise further migration of PFAS from the site, to ensure safer, cleaner grounds for future infrastructure development.
The challenge
The primary objective of the project was to remediate the PFAS-impacted soils to minimise the flux of PFAS to offsite receptors via surface water and to groundwater by infiltration. For 18 months – August 2022 to December 2023 — our team addressed the complexities of PFAS remediation and undertaking construction works at a live airport. Working near an active joint user airfield required the Defence exercise activities to be understood and contractually planned prior to works to avoid unnecessary stand-down time and high-quality dust control to avoid stop work notices.
The process was divided into two stages to focus on PFAS-impacted soil remediation through excavation and treatment, aiming to reduce PFAS mass flux offsite and to environmental receptors.
Along with the technical aspects of decreasing PFAS presence, the project included a civil objective to reinstate and improve the ground formation, including main drainage culvert to limit groundwater recharge and improve airfield drainage.
Our response
Our technical knowledge in the field of contaminated environmental services within Defence coupled with our ‘turnkey’ delivery model history, enabled us to provide the approval pathways, technical management, on-site sampling and the relevant technical reporting requirements that a remediation subcontractor could not provide under a single contract.
Our team delivered an extensive drilling program to delineate the PFAS impact, including the review and revision of an existing remediation action plan (RAP) and refining the 3D models; identifying ~7,000 m3 of soil with > 1 mg/kg PFAS containing about 80 kgs of PFAS for remediation. We also conducted treatability trials to assess immobilisation of PFAS soil using powdered activated carbon (PAC). Determining that 1.5% w/w PAC reduced the leachability of PFOS + PFHxS by > 99%.
The PFAS-impacted soil was managed in line with Stockholm Convention and Commonwealth guidance, addressing reinstatement and revegetation of the site. The works also focused on upgrading an existing drainage channel; including soil treatment, installation of an interceptor trench and lining with a synthetic membrane to reduce impact to throughflow water, minimise erosion, and further reduce the flux of PFAS to groundwater from surface water during heavy rainfall events.
The impact
The remediated site has been appropriately compacted to allow for future infrastructure to be built safely within the area, breathing new life to the RAAF Townsville facilities.
The swale drain has been treated with a blended road base with 2-3% PAC to a depth of 0.2- 0.5m and compacted. It has been lined with an anti-cracking impermeable, fibre-reinforced, geosynthetic composite concrete cloth with a compressive strength of 80MPa. This aligned with the objective of minimizing vadose zone runoff and reducing infiltration of contaminated water through the soil profile. The alternative design also provided a more constructable, less erodible and cost-effective solution that will require less long-term maintenance. A substantial additional mass of PFAS was identified and removed.
The project was completed on time, within budget, without lost time, injuries or environmental incidents. Operations at the airport continued uninterrupted during the remediation.