Traditional remediation methods often rely on pumping and treating groundwater over long periods, which is both costly and technically complex. Researchers at the Swedish Geotechnical Institute therefore wanted to investigate the effectiveness of an activated carbon barrier.
In 2023, a 70-metre-long subsurface barrier was installed across a contaminated groundwater plume at a fire-training site near Örnsköldsvik Airport. The barrier contained colloidal activated carbon, a finely milled adsorbent material that binds PFAS. As contaminated groundwater passes through the barrier, PFAS is retained by the activated carbon rather than continuing towards lakes, watercourses and drinking water sources.
The researchers monitored the site for two years, carrying out monthly groundwater sampling from more than 50 groundwater observation wells.
“We observed a strong effect from the barrier from the outset, but what happened subsequently was that the effect continued to increase throughout the two years of monitoring. Because the geology at this site is common in many parts of Sweden, this is a method that could potentially be applied at several other locations in the future,” says Robert Earon, hydrogeologist at the Swedish Geotechnical Institute (SGI).
Concentrations reduced to drinking water quality levels
The results show that, inside the barrier, PFAS levels fell by more than 99.9%, dropping from over 100,000 nanograms per litre to as little as 1 nanogram per litre.
These concentrations are comparable with levels currently accepted for drinking water in Sweden. Further downstream, concentrations also declined substantially. In surface water, reductions of approximately 97-98% were recorded by the end of 2025.
The study also showed that the barrier retained more than the PFAS compounds typically included in routine analyses. It also captured non-target precursors, chemical compounds that can be transformed into PFAS.
Before the barrier was installed, the researchers carried out a comprehensive characterisation of the site's geology and groundwater flow conditions. This included hydraulic testing, groundwater measurements and digital groundwater modelling to determine where the treatment would have the greatest impact. This proved to be crucial to the outcome.
Can limit the spread of PFAS
One question still remains: how long will the barrier continue to effectively reduce the spread of PFAS? Because the PFAS source remains in the upgradient source zone, the effectiveness of the activated carbon will eventually decline, although this process may take decades for some of the most problematic PFAS compounds. Continued monitoring will therefore be required to assess the long-term performance of the barrier.
“We have observed exceptionally high treatment efficiency over a two-year period, and there are no indications that this performance will not continue over a much longer timeframe. However, we naturally need to understand how long. What we do know is that the barrier works under field conditions and that full-scale barrier remediation can be an effective method for limiting the spread of PFAS in natural groundwater systems,” says Robert Earon.
The project is funded through the Swedish Government's appropriation 1:4, Remediation and Restoration of Contaminated Areas. It forms part of SGI's government assignment on research and knowledge development relating to PFAS-contaminated sites.
Scientific article:
Earon, R., S. Sahlin, M. Pettersson, et al. 2026. “In Situ Treatment of Target and Precursor PFAS in a Groundwater Plume Using a Permeable Barrier of Colloidal Activated Carbon.” Remediation 36: e70079. https://doi.org/10.1002/rem.70079.
