At Bromma Stockholm Airport, fire drills have previously been performed at a location outside the current airport confinements. Fire drills were performed with extinguisher foams containing toxic perfluorooctanesulfonic acid (PFOS), which have polluted the site. Harmful effects of PFOS include but are not limited to damages to the endocrine system. The contaminant is relatively soluble and can be transported by water. The aim of this thesis was to model groundwater flows and PFOS transport in the area. In order to build the model, data was gathered from databases, literature studies and field investigations. The field investigations included geophysical measurements. The model was built in the software Visual MODFLOW Classic. It was used to increase knowledge of hydrogeological conditions in the area, predict the fate of PFOS leaching from the site and suggest preventative measures for preventing the spread. The model results showed that the contaminant is transported towards the current airport area by means of groundwater at a slow rate and with low concentrations. Additionally, high concentrations of PFOS will remain in soil and groundwater at the study area for several hundreds of years, according to model results. Preventative measures should therefore be focused on minimizing risks to frequent visitors to the site, which is currently used as a golf course.