Sampling proficiency test for the estimation of uncertainty in the spatial delineation of contamination

The performance of samplers in their ability to delineate spatially a region of contamination has been assessed by the use of a sampling proficiency test (SPT) on a synthetic reference sampling target (RST). The RST was used to compare the participant's estimate of the extent of contamination with that of the assigned dimensions. These dimensions were defined based on the analyte spiked into the site and verified by the collection of field samples. Nine participants collected soil samples independently using protocols selected on the basis of their own professional judgement. Test portions from these samples were then analysed by the SPT coordinator under repeatability conditions. The resulting concentration measurements were sent to each participant for them to make their own interpretation of the spatial distribution of the contamination above a defined threshold concentration. For each participant the reported spatial extent of contamination was compared with the assigned dimensions of the hot spot to provide a score based on a novel adaptation of the International Harmonised Protocol. The consensus of the participants' spatial delineations that were deemed fit-for-purpose using a cost-effectiveness scoring system were used to estimate the area within which the assigned hot spot was positioned with 95% confidence. The score for this 'consensus' hot spot area was 0.64 when compared with the assigned dimensions, where a score of 0 indicates perfect spatial delineation and a score of less than or equal to3 indicates acceptable performance for this particular investigation.