A highly concentrated foaming liquid containing Per- and Polyfluoroalkyl Substances (PFAS) was accidentally released into an ephemeral creek after entering a stormwater drain. Our client received in succession a clean-up notice, an environmental evaluation notice and an environmental protection order from the environmental regulator. Because of our extensive characterisation and forensics experience, we were engaged as an environmental consultant.
After initial emergency clean-up activities were completed, our team conducted a staged, multi-media assessment of the area to determine the presence and extent of elevated PFAS concentrations in the groundwater, surface water and sediments, and in biota tissues collected in the local surface water system. Multivariate statistical data visualization techniques were used with the data to refine the conceptual site model and differentiate between any detected PFAS originating from sources other than the spill being investigated.
Working with the analytical data attributed to the spill event, these analyses were then used to conduct a Tier 1 Human Health and Ecological Risk Assessment (HHERA) which identified that the elevated PFAS concentrations represented a potential environmental risk and that further characterization and remedial activities were warranted, and also that the limits of the investigation should be expanded to include nearby catchments and in a marine park downstream.
We collected supplemental samples to conduct a Tier II HHERA. This assessment demonstrated that the risk to human health from exposure to the contaminated soil, surface water and biota was low and acceptable by virtue of the limited public access and a lack of complete pathways. However, further evaluation was required to determine the ecological risk that was assessed as unacceptable and therefore further removal of the secondary sources was warranted.
Staged soil clean-up and validation activities removed the soil and sediments that had PFAS concentrations above background levels, accounting for leachability and the risk of mobilization. Part of the excavation was next to a 5m-high retaining wall, so our team designed a detailed geotechnical assessment and monitored stability through daily surveying of settlement, excavating in small sections, and ensuring appropriate compaction of backfill.
An in-situ investigation was performed to determine the leachable PFAS concentrations from a potentially impacted concrete stormwater culvert under a main road – the removal of which would be a significant civil works undertaking. This investigation facilitated agreement that this culvert posed limited risk and could remain.
Our investigation report and Tier II HHERA were reviewed by an auditor, presented to the regulator, and formally accepted as fulfilling the regulatory notices. In addition to this successful achievement of compliance, through the HHERA, the ability to differentiate PFAS origins and the leachability testing we were able to reduce the scale and complexity of the remedial activities ultimately undertaken.
* This work was performed by Golder professionals who joined WSP in an acquisition completed in 2021.