Estimation of sampling uncertainties: implications for regulation of contaminated land

Methods have recently been devised for the estimation of measurement uncertainties due to field sampling. These methods have revealed very large discrepancies between the estimated levels of lead in one area of contaminated land. The precision when sampled by different organisations using the same protocol was +/- 55% (95% confidence). This uncertainty is due entirely to the sampling, rather than the analytical measurement /1/. When sampling organisations used whatever sampling protocol that they considered appropriate, and analysed their own samples, the inter-organisational precision was+/- 72% /2/. The existing criteria for the classification of contaminated land in the UK depend on the use of threshold trigger concentrations. With such large values of measurement uncertainty in the estimated concentration of the contaminant due to field sampling, there is a large probability of the erroneous mis-classification of land. This has legal, financial and possible health implications from both the unnecessary remediation of 'uncontaminated' land and the erroneous acceptance as uncontaminated of land that is in fact contaminated. Further studies of a variety of contaminated sites with a range of contaminants are required to clarify the typical contributions to the measurement uncertainty of both the sampling and analytical procedures. New classification criteria for contaminated land are required that allow for not just the estimated concentration of the contaminant, but also the overall measurement uncertainty in its estimation.