Stipendiatstillinger til NGI (2017-2021)

The use of firefighting foams containing fluorinated "forever chemicals" at airports and military bases have resulted in emissions to soil causing groundwater contamination and further spreading of these chemicals in the environment. "Forever chemicals" are persistent, bio accumulative, mobile and of great concern for human health and the environment. This work confirms that increasing amount of large precipitation events, due to climate change, will increase spreading of "forever chemicals" in the environment. However, there are several important variables which determine the rate and amount of these chemicals being leached, how long they will be in soils and if they are a potential long term source of contamination. "Forever chemical" are a human made organic group of chemicals with over 5 000 per- and polyfluorinated alkyl substances (PFAS). They are of great concern in the scientific community, among the environmental policy makers and stakeholders around the world. The concern is due to high environmental persistency and ubiquitous environmental presence. Despite the ubiquitous presence of PFAS in the environment, fate and transport in soil is not well understood. The comprehensive understanding of PFAS is complex due to unique chemical properties of PFAS which include; heat resistance, water, dirt and oil repellence, resistance to chemical, biological and physical degradation processes. PFAS present specific challenges due to their molecular structures combining a hydrophobic tail with a charged head group giving them strong surfactant properties. The properties which makes PFAS valuable for their use, give high environmental persistency, mobility and high potential for bioaccumulation, biomagnification and toxicity to organisms making PFAS a great cause for environmental concern. The use of PFAS in aqueous film-forming foams (AFFF) started in the 1960's and resulted in superior firefighting abilities. This work investigated the importance of infiltration of water into the soil and the effect different rates and amounts of water have on the downward movement on PFAS in the soil. The amount of water in the soil, called porewater, varies in the soil depending on how much water that infiltrates into the soil. This creates varying amount of air voids in the soil and this varying amount of water and air voids in the soil has been seen to influence the transport PFAS in the soil. Through column studies and field work, infiltration of water in sandy soil for several infiltration scenarios have been investigated. Column studies simulating natural infiltration of snow melting and fall precipitation gave insight in infiltration rates influence on spread of PFAS. Testing soil washing in the field gave insight in transport of PFAS and showed promising results as a remediation method. The results show that the rate of water infiltration and the amount of water infiltrating influence the transport of each PFAS differently, depending of the chemical properties and soil and site properties. Molecular size and water solubility of PFAS vary and influence transport in soil as water infiltrate. However, PFAS influence and lower the surface tension of water and therefore also the contaminated porewater which is of importance for the fate and transport of PFAS, especially at high enough concentrations to significantly lower the surface tension of the porewater. The results show that properties of the soil, like organic content and size of the soil particles influence the transport of these chemicals due to sorption and desorption mechanisms. The historic use of firefighting with foam and water at an AFFF contaminated site also influence the fate and transport of PFAS from source zone. Not only because the amount of AFFF added, but because AFFF contain other organic components. Results show that dissolved organic matter in the AFFF is high and that the total organic carbon (TOC) in the soil increase after AFFF has been added.The results show that to determine the most sustainable and environmental acceptable clean up action for an AFFF source zone, the site investigation must include soil characterization including all organic matters, both natural and added by the AFFF, soil grain size distribution, a hydrological description of the site including precipitation and infiltration investigations and water transport in the soil to the groundwater in addition to a historic use of the site for firefighting training. The fate and transport of PFAS at an AFFF site which has continuously been used for firefighting training will be very different than a location with only one firefighting foam event. The natural and artificial weathering of the AFFF PFAS contaminated soil site is of great importance for the fate and transport of PFAS in the soil

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