SUMMARY

Purpose of the Study

Immobilisation of PFAS in soil is now considered a viable and cost-effective remediation approach. This approach uses sorbents to reduce the leaching of PFAS into ground water and surface water reducing the risk to human health and the environment. It is particularly suitable for managing large soil volumes containing relatively low PFAS levels, where other thermal and washing techniques are not viable from a cost or capacity viewpoint.

Although the PFAS chemicals are rendered ‘immobile’ by this process, they still remain in the soil and so proving the long-term stability of the process is critical for giving peace of mind to future generations that the PFAS will not re-leach.

The question of long-term robustness is particularly relevant where treated soil is to be reused on site as part of a circular economy approach which not only reduced costs, but also enables us to beneficially reuse otherwise healthy soil as a resource, avoiding unsustainable landfill disposal.

Methodology

Independent data from Europe, USA and Australia will be presented that shows the stability of immobilised soils across a wide range of environmental conditions including pH, competing ions, freeze/thaw, wet/dry and repeated leaching events. A number of techniques for simulating long-term stability will be explored including the likes of the DIN, USEPA LEAF, MEP and TCLP-based methods.

Field-scale data from independent projects in Europe (2) and the USA (1) that have been monitored for up to 5 years will be presented as evidence of ‘real-time’ data from the field to validate lab-scale simulations. Bioavailability data showing reduced uptake of PFAS into plants and earthworms will also be summarised.

Summary of Findings/Results

The presentation of independent data from various projects around the world will put a case forward that immobilisation is generally a very robust technique across a wide range of environmental conditions, as evidenced by both lab-scale simulations and some field demonstrations after 5 years of monitoring. Future considerations for developing better methods for testing the robustness of the immobilization solution will be discussed.

Conclusion/Take Home Message

The long-term stability of PFAS immobilisation in soil is a critical question for all project stakeholders including regulators and the community. The independent data presented here from several global projects will show that the process is generally very robust across a wide range of environmental conditions using a range of sorbents. Some thoughts on how we can better simulate long-term stability will also be thrown up for debate.

Significance/Contributions of the Study

Immobilisation is now considered a viable and cost-effective option for the management of PFAS contaminated soils. Long-term stability is the number one question that remains critical to regulators to ensure peace of mind for future generations. Because we can only simulate what happens over decades or centuries, the data being produced by current test methods is critical to answering the question; “How Long is Long Enough?”.