Widespread use of poly- and perfluoroalkyl substances (PFAS) globally has raised concerns about potential legacy environmental contamination and subsequent impacts on human health. PFAS compounds are persistent and bioaccumulative, and their toxicity and long-range transportation of PFAS compounds has meant that they are ubiquitous in the environment and been detected globally in several sample types. Research in Ireland has indicated the presence of PFASs in a variety of media, including surface water. The main objective of this work was to characterise risks by sampling surface water from 20 sites along the River Liffey, between a tributary to the sea. It was found that concentrations of up to 2 µg/L of individual PFAS compounds were detected along the river. To interpolate the nature and distribution of PFAS compounds and identify potential links to upgradient sources, a 4-step hierarchical process was used. 1. Geographical proximity - The River Liffey flows through the centre of Dublin, Ireland and is known to have legacy contamination. Known primary and secondary sources of PFASs in the catchment of the river Liffey include civil (airports and fire stations), anthropogenic (wastewater treatment facilities and waste facilities) and industrial pressures (chemical manufacturing plants, paper processing facilities and industries with emissions licences). 2. Chemical footprint - Individual compounds have unique properties and different combinations are used by industries for specific purposes. By identifying unique compounds and distinguishable compound rations, a specific diffuse PFAS source can be inferred. 3. Dimensional calculation – A solute transport model was employed to predict the spatio-temporal fate of PFAS and infer proximity to industrial sources. 4. Dimensional modelling and cluster analysis was employed to refine the source identification. With the data obtained, the occurrence of different PFAS substances was linked to potential civil, anthropogenic and industrial sources in the River Liffey catchment.