Pilot-scale trials show: PFAS can be stopped before reaching groundwater
Photo: SGI/Robert Earon
The spread of PFAS from contaminated soil to groundwater can be reduced by more than 99 per cent. This is shown by pilot-scale trials conducted by the Swedish Geotechnical Institute (SGI) in heavily PFAS-contaminated soil and groundwater at fire training areas near airports. In one of the tri-als, PFAS-contaminated water passed through an activated carbon barrier. PFAS levels were reduced by 99.99 per cent, to levels comparable with the current limit value for PFAS in drinking water.
PFAS can spread from a contaminated site through the soil and into groundwater. In Sweden, several municipalities have taken groundwater sources out of use or installed costly treatment equipment because of PFAS in drinking water. PFAS contamination can pose risks to human health and the environment. These substances break down very slowly in nature and can spread from soil to groundwater and onwards to drinking water, lakes and watercourses.
Activated carbon reduces the spread
SGI has tested and evaluated remediation methods for reducing the spread of PFAS. The projects have been carried out over four years as part of a governmental assignment on research and increased knowledge of PFAS-contaminated sites. The work covers four remediation methods: soil washing, stabilisation using activated carbon, thermal treatment (heat treatment) and air sparging.
In the trials, stabilisation using activated carbon has proved highly effective at reducing the spread of PFAS to and within groundwater. The method involves mixing activated carbon into the soil or using it in a barrier through which contaminated groundwater passes. The activated carbon binds PFAS, retaining the substances and preventing them from being transported with the groundwater.
Immediate effect
In one trial, activated carbon was mixed into PFAS-contaminated soil above the water table. PFAS levels in the soil water were reduced by more than 99.98 per cent. The effect was almost immediate, showing that the spread from a contaminated source area can be stopped within a short period of time.
In another pilot-scale trial, an activated carbon barrier was installed downstream of a fire training area in Örnsköldsvik. As the contaminated groundwater passed through the barrier, PFAS bound to the activated carbon. After approximately a year and a half, PFAS levels in the water leaving the barrier had fallen by 99.99 per cent, to levels comparable with the current limit value for PFAS in drinking water.
“Stabilisation using activated carbon is a method that can already be used to effectively reduce the spread of PFAS in groundwater. The method does not break down PFAS, but it can greatly reduce their spread. This is an important step towards protecting groundwater, the environment and human health,” says Michael Pettersson, a researcher in environmental chemistry and project lead at SGI.
The method depends on the site
Soil washing is also a promising method for treating PFAS-contaminated soil, particularly sandy and gravelly soils. SGI’s trials show that washing with water can achieve a removal efficiency of around 90 per cent. When water is combined with air and surfactants, the removal efficiency can increase to around 97 per cent. The method involves excavating the soil, separating it into different particle sizes and washing it so that a large proportion of the PFAS contamination can be separated out. The most highly contaminated soil, wash water and foam then need to be handled safely.
“There is no single method that works everywhere. The choice of method must be based on the conditions at the site, the types of PFAS present and the risk that needs to be managed,” says Michael Pettersson.
Thermal treatment (heat treatment) can be effective at removing PFAS from soil, provided that the temperature is sufficiently high and the treatment time sufficiently long. At the same time, the results show that PFAS are not always completely broken down and that residues need to be carefully managed. Air sparging was assessed as having limited benefits as a remediation method.
‘Start using the methods’
“The results of the pilot-scale trials show that there are methods that can effectively stop the spread of PFAS to groundwater. We recommend that proven methods should be applied where they are suitable, while their effects are monitored over time. The risk of waiting is that PFAS will continue to spread. This could make remediation more complicated and costly in the future. It could also result in contamination reaching new and previously unaffected areas,” says Mikael Stark, Head of the Department of Soil and Water Environment at SGI.
The next step is to monitor how the methods perform over time and to put the results to practical use. In the report, SGI points out that work on PFAS-contaminated sites needs to focus more on reducing spread and risks, rather than solely on the concentrations that remain in the soil. This could make it possible to use a wider range of remediation methods and accelerate work on PFAS-contaminated sites.
About the Government assignment
The projects were carried out between 2022 and 2026 as part of a governmental assignment with the goal of researching remediation methods of and increasing knowledge relating to PFAS-contaminated sites. The work was funded through Government appropriation 1:4, Remediation and restoration of contaminated sites.
The assignment has focused on developing, testing and evaluating remediation methods for PFAS-contaminated soil and groundwater and on translating research findings into knowledge that can be put into practice by government agencies and other stakeholders. The overall aim is to help increase the pace of remediation so that more contaminated sites can be addressed. The assignment has been carried out in collaboration with the Geological Survey of Sweden (SGU), the Swedish Environmental Protection Agency, academia and other government agencies.
The results show that there are remediation techniques that can be used to effectively reduce PFAS levels in soil and the spread of PFAS to groundwater. The choice of method must be based on the conditions at the site, the types of PFAS present and the risk that needs to be managed.
In July 2026, the Swedish Government decided to extend and further develop the assignment for the period 2026–2030. SGI will continue its work on research and knowledge sharing relating to site investigation, assessment and remediation. The assignment will also include suitable pilot projects at state-owned contaminated sites.
