Title: Statistical Assessment of Contaminated Land: Some Implications of the Mean Value Test (Technical Bulletin 12) 
Resource Type: document --> technical publication --> methodology description 
Country: United Kingdom 
Year: 2006 
Author 1/Producer: CL:AIRE 
Other Authors/Producers: Masi, Paulo., Morgan, Philip., (Environmental Simulations International) 
Author / Producer Type: Professional / trade / industry associations, institutes or networks 
Publisher: CL:AIRE 
Report / download web link (=direct link): http://www.claire.co.uk/pdf_usr/tb12_stats_final.pdf  
Format (e.g. PDF): PDF 
Size: (e.g. 20mb) 400 
EUGRIS Keyword(s): Contaminated land-->Contaminants-->PAH
Contaminated land-->Risk assessment-->Models
Contaminated land-->Risk assessment-->Tools and procedures
Contaminated land-->stats, registers, inventories etc
Short description: This bulletin provides a discussion on the 'Mean Value Test' presented in Contaminated Land Report 7 (CLR7) and suggests alternative techniques to reduce the risk of underestimating the true 95% Upper Confidence Limit of the sample mean. 
Long description: Statistical methods are commonly used to guide decision-making in many regulatory contexts. For the assessment of potentially contaminated land, it is common practice to use the ‘Mean Value Test’ approach defined in Appendix A of Contaminated Land Report 7 (DEFRA and Environment Agency, 2002). This defines the estimation of the 95% Upper Confidence Limit of the mean soil concentration of a contaminant (95%UCL, also referred to as US95) and its use as the appropriate value to be compared with the relevant soil guideline value (SGV) or site-specific assessment criterion (SSAC). This 95%UCL is meant to provide a reasonably conservative estimate of whether the measured concentration is acceptable, considering the uncertainty and variability associated with site investigations. However, when applied to real environmental datasets, the ‘Mean Value Test’ can actually prove to be a non-conservative choice that may wrongly categorise a potentially contaminated site as ‘clean’. This bulletin illustrates how such a situation could arise, highlights the implications and introduces alternative appropriate methods to derive the 95%UCL of the mean soil concentration. 
Link to Organisation(s): CL:AIRE (Contaminated Land: Applications in the Real Environments)
Submitted By: Mr John Henstock WhoDoesWhat?      Last update: 15/02/2007