Rationale and approach\ud Soil geochemical data available from the BGS G-BASE (Geochemical Baseline Survey of the Environment) project has indicated that As (arsenic) and Ni (nickel) may be naturally elevated above their respective SGV’s (soil guideline values) for residential land use over large areas of England. This does not imply that soil in these areas pose a significant risk to human health, but that considerable effort may be needed in undertaking risk assessments to determine whether there is the possibility of significant harm. To further their understanding of this potential problem, ODPM commissioned the British Geological Survey to generate maps covering the two growth areas (Milton Keynes/ South Midlands and London-Stansted-Cambridge), highlighting the likelihood of naturally elevated soil As and Ni concentrations exceeding their respective SGV’s.\ud The assessment of baseline soil geochemistry presented in this report was based upon:\ud 1. Soil geochemical data for As and Ni from the BGS G-BASE project\ud 2. BGS 1:50,000 scale parent material (parent material) maps of the study region\ud 3. Geochemical data from other published sources (including the Wolfson Geochemical Atlas and National Soil Inventory)\ud We adopted a three-stage approach to classifying the parent material polygons into the likelihood of the soil developed from them exceeding the SGV’s for As and Ni; the three likelihood classes are: unlikely, moderate likelihood and strong likelihood. The first stage relates to those parent material types for which soil geochemical data are available. The second stage concerns those areas where soil geochemical data is not available for parent material types within the study region, but such data exists immediately outwith the study region. Hence, we have used these data as a proxy to classify the parent material types in the study region. Third, for areas where no BGS soil geochemical data exists within or outwith the region, we have used representations of geochemical data from the Wolfson geochemical atlas to classify these parent material types.\ud The outputs from the study were three GIS layers depicting:\ud 1. the confidence we have in our predictions of likelihood for exceeding the SGV’s\ud 2. the likelihood (unlikely, moderate, strong) of exceeding the As SGV for residential land use (20 mg/kg)\ud 3. the likelihood (unlikely, moderate, strong) of exceeding the Ni SGV for residential land use (50 mg/kg)\ud Confidence and likelihood predictions\ud We have a high level of confidence in our prediction of the likelihood of exceeding the SGV’s for As and Ni for around three-quarters of the total land area. For around half the total land area there is a moderate likelihood that the As SGV for residential land use will be exceeded. More importantly, there are a series of parent material types covering around 15% of the total land area generally in the north and west of the study region over which soils have a strong likelihood of exceeding the 20 mg/kg As SGV for residential land use. Considerable funding may be required in undertaking site-specific risk assessments in these areas prior to residential development. For 40% of the total land area, generally over the central and western areas of the study region, there is a moderate likelihood that the Ni SGV for residential land use will be exceeded. Where there is no data available for unique parent material polygons that cover only small parts of the growth areas, they were classified ‘no data’. If these occur in areas considered important in terms of future development, it would be relatively inexpensive to establish the likelihood of the soil exceeding the SGV’s for As and Ni by undertaking a limited amount of further soil sampling and analysis
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