Methods used in the Tellus geochemical mapping of Northern Ireland

The Geological Survey of Northern Ireland (GSNI) and the British Geological Survey (BGS) have completed geochemical surveys of Northern Ireland in three phases of sampling and analysis. Sampling and quality control were undertaken according to the G-BASE protocol of BGS, as follows: • Stream sediment and stream waters surveys in 1994-96 (2,908 sites in the west) and in 2004-06 (2,966 sites in the east). The sampling distribution averaged one site per 2.4 km2. • Soil sampling surveys of rural areas and of selected urban areas in 2004-06. 6,862 sites were sampled at an average of one site per 2 km2. Two samples were collected at each site, from depths of 5-20 cm and 35-50 cm. • Soil sampling of the urban areas of Belfast and Londonderry, at 1,315 sites at a distribution of four sites per km2. Analyses were undertaken by laboratories (including BGS), selected by open tender, for a range of inorganic compounds and trace elements, as follows: • Stream sediment and shallow soil samples were analysed by X-ray fluorescence (XRF) spectrometry. • Shallow and deep soil samples were analysed by inductively coupled plasma (ICP) spectrometry. • Deep soil samples were analysed for selected elements by fire-assay; • Stream water samples were analysed by ICP and ion-chromatography. One quarter of the urban soil samples (one site per km2) were analysed for a range of semivolatile organic carbons (SVOCs). Digital databases and images of the results have been produced.