Groundwater Flow and Transport Modelling of PFASs in Åkersberga

Sammanfattning: Per- and polyfluoroalkyl substances (PFASs) are a group of man-made organic chemicals that have been commercially used since the 1950s in many consumer products, including impregnated textiles, impregnated paper, nonstick products (e.g., Teflon), cleaning agents, and in firefighting foams. However, PFASs have in recent years received increasing public attention due to their persistence, bioaccumulative potential, and potentially toxic effects on humans and animals. Firefighting training sites have been identified as one of the most important sources for the spread of PFASs in the environment, due to the use of PFAS-containing firefighting foam of type AFFFs (aqueous film forming foams). This has resulted in contamination of both drinking water and groundwater in several municipalities in Sweden. At the former fire station in Åkersberga, AFFFs were handled and used during the fire-training exercises. WSP Environmental Sweden has performed a preliminary investigation on site and elevated levels of PFASs in both soil and groundwater were observed. Since the property is located next to a railroad track, there is a concern that PFASs will spread through the railroad track towards the nearby Åkers canal. The aim of this master’s thesis has therefore been to map the transport of PFASs in groundwater from this former fire station. A groundwater flow model was first constructed in the software program Visual MODFLOW. The groundwater model was then used as a basis for the construction of a transport model with MODPATH and MT3DMS. The transport of four PFAS homologues was modeled; perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), 6:2 Fluorotelomer sulfonate (6:2 FTS), and perfluoropentanoic acid (PFPeA). The result of the groundwater modelling showed that groundwater from the property flows towards the southwest and then further towards Åkers canal. The approximated velocity of a water molecule varied between 270 m/year and 400 m/year. The transport modelling showed that all four PFAS homologues traveled towards Åkers canal via the railroad track and that the short-chain PFAS homologues (6:2 FTS and PFPeA) traveled longer and faster than the long-chain PFAS homologues (PFOS and PFOA). The approximated velocity of the contaminant plume for the concentration 4.5 ·10−5 mg/L was 0.6 m/year for PFOS, 3 m/year for PFOA, 8 m/year for 6:2 FTS, and 16 m/year for PFPeA.