30. Spatial distribution of soil geochemistry in geoforensics Alastair Ruffell 1 and Jennifer McKinley 1 Soil geochemistry may be applied in the science of geoforensics in two ways: to establish the provenance of samples and to inform the question of sample variability. Tellus data can assist in answering on a broad scale the provenance question, ‘where may this sample have come from?’ Although the Tellus data are too widely spaced for precisely locating the source of a sample, the spatial variation in geochemistry may exclude areas where a sample of unknown origin came from. Using soil in geoforensic investigations Geoforensics is ‘the application of selected geoscience techniques to criminal (domes- tic, international, terrorist, humanitarian, environmental, fraudulent) investigations of what happened, where and when it occurred and how and why it took place’ (Rufell and McKinley, 2008). Te discipline has been divided into two overlapping areas of research and practice (Pirrie, 2009): trace evidence and search/location. Trace evidence analysis is usually conducted in order to establish the characteristics of samples from (i) a scene or locus, (ii) control or alibi locations (both being known) and (iii) a suspect item of which the origin is unknown and that commonly might be a vehicle, footwear, clothing, tools or suspected fake items. Soil mineralogy and microbiology are used to these ends but are never used in a direct attempt to ‘match’ soil samples. Although each soil is a unique mixture of organic and inorganic materials, there is always the possibility of two or more diferent locations having soils that our current methods of analysis cannot distinguish. For this reason, the forensic pedologist employs the exclusionary principle (Morgan and Bull, 2007). Tis states that the mineral and organic characteristics shown by samples from the scene of crime and the suspect are more similar than any control samples or those in a database, thus excluding all possibilities except that they have the same origin. Trace evidence (for example on footwear, clothing or vehicles) and the scene of crime are sampled at a far more detailed scale than soils and sediments collected in regional soils surveys. Tis precludes use of such regional databases in many forensic scenarios; it is a simple matter of diferences of scale. Nonetheless, for a regional picture of the variation in soil geochemistry, databases 1 Queen’s University Belfast. 387 How to cite this chapter: Rufell, A. and McKinley, J.M., 2016 ‘Spatial distribution of soil geochemistry in geoforensics’ in M.E. Young (ed.), Unearthed: impacts of the Tellus surveys of the north of Ireland. Dublin. Royal Irish Academy. DOI:10.3318/ 978-1-908996-88-6.ch30