This paper discusses the 2008 Chartered Institute of Environmental Health (CIEH) and CL:AIRE ‘Guidance note on comparing soil contamination data with a critical concentration’. It discusses the different statistical tests and the underlying assumptions within the document with reference to worked examples. We conclude that in contrast to CIEH/CL:AIRE 2008, the t-test can be used for the Environmental Protection Act 1990 Part 2A scenario whatever the distribution of the underlying data set, as long as the dataset is not negatively skewed. The implications of sample size and statistical power are also considered. Collecting a very limited number of samples will mean that the assessor has little chance of rejecting the null hypothesis. In this situation a non-significant result is difficult to interpret and the compliance monitoring is largely a pointless exercise.