An analysis of PAH soil contamination in south east England: A case study leading to an evidence-based portfolio and process route map

Abstract

Through the regulatory planning process, UK local government has detailed information on contaminants for most of their development (predominantly brownfield) sites, dating back to 2000. The soil data collected includes information on polycyclic aromatic hydrocarbons, PAH, a group of potentially carcinogenic chemicals. This paper describes how an evidence-based portfolio of PAH contamination has been generated from this site measured dataset and developed into a process route map to facilitate PAH data analyses in other regions. The PAH data, site history and borehole information were extracted from 1990 to 2019 records of 120 brownfield sites in Elmbridge Borough, a suburban region southwest of London. The data were interrogated using spatial and depth analysis, diagnostic ratios and chemical composition analysis. Elevated PAH concentrations were predominantly found within Made Ground and indicated that the major source was anthropogenic deposition. The results from the diagnostic ratios indicated a pyrogenic, non-traffic related source for 90% of the samples. Statistical analysis showed low median concentration values with a few high outliers for all PAHs studied. Most soil samples had a similar PAH composition, irrespective of site history or soil sample description. This PAH composition was found on residential sites, where the likely source was coal-based burning. The data thus suggested a coal-based source for most of the PAH contamination in the study area. The results for PAH contamintation on brownfield sites in suburban Surrey were similar to a UK study for a UK coal-based industrial area. The PAH concentrations found were significantly higher than those reported in other international studies, however this was partly due to different sampling techniques. A process route map is proposed which incorporates both the analytical processes and the evidence-based portfolio of key findings. This route map is portable to different regions and consequently can be used as a platform for the analysis of PAH data to inform developers and regulators of potential sources and distribution in a region.