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Section 3: Site investigation techniques |
Environmental Geology Research, Department of Geology, Imperial College, London SW7 2BP, UK
The measurement process in environmental studies on contaminated land comprises sampling and analysis with the objective of estimating the values of the analyte concentrations. The estimated mean concentration has a real variation but also a variation due to errors originating from sampling and analysis. Inter-organizational trials, in the form of collaborative trials and proficiency testing, is a well established methodology for the estimation of the analytical uncertainty. However, such trials applied to sampling are in a very early stage of development. The objectives of inter-organisational sampling trials are to reveal discrepancies due to sampling at a particular site, to estimate measurement uncertainty on the estimates of mean metal concentrations at the site and ultimately to improve reproducibility of the participants' results. The very first pilot sampling trial was conducted on a smelter-contaminated site in Derbyshire. The results showed the feasibility of conducting sampling trials and also that errors originating from sampling tend to be much greater than the analytical errors. A second inter-organizational sampling trial was conducted on Hounslow Heath, West London, which is an old landfill site with different contamination characteristics. The results from both trials have shown large discrepancies in estimates of mean metal concentrations in soils by factors up to 2.5 times. The role of heterogeneity of the distribution of the contaminants is a limiting factor when conducting such trials and their usefulness in measuring uncertainty of metal concentration at a particular site has been demonstrated.
