Urban soils geochemistry and GIS-aided interpretation : a case study from Stoke-on-Trent

The systematic geochemical mapping of urban soils has been undertaken by the British Geological Survey (BGS) Geochemical Surveys of Urban Environments (GSUE) project since 1992 and to date 21 urban centres have been sampled. The city of Stoke-on-Trent was chosen for a review of GSUE methods as the area contained sufficient sample numbers (approximately 750) and additional information such as geology and land use to allow an assessment of sampling techniques, data presentation and the applicability of geochemical data to wider environmental problems. Separate chapters in this report address: • The presentation of urban geochemical data, both within the urban area and in relation to rural geochemical data • The possible controls on soil geochemistry and distributions of chemical elements in the area • The application of geochemical data to risk-based human exposure and groundwater vulnerability assessments in relation to chemical elements in urban soils The results demonstrate that the geochemistry of soils in Stoke-on-Trent primarily reflects that of the soil parent material. In areas underlain directly by natural bedrock and drift deposits, these play an influential role in soil chemistry, despite the increased incidence of diffuse pollution in urban compared to rural areas. In contrast, element distributions in soils developed over made ground show that this substrate has a major, often detrimental effect on soil quality. However, it should be noted that much of the waste material used as fill (prior to modern regulatory systems) in Stoke-on-Trent is very base-rich providing buffering against acid soil conditions. Therefore, the mobility of many potential harmful metal and other trace elements is likely to be restricted in the neutral to alkaline soils of the area than may otherwise be the case in ‘natural’ soils. This study has generated a series of recommendations to inform future geochemical surveying strategies ranging from the inclusion of additional analyses, to the application of the data for further risk assessment studies.