When the retrospective power of a set of samples is below the required design objectives, double sampling can raise it. Insufficient retrospective power can occur for a number of reasons, most commonly because:
- The spatial variability in residual radioactivity concentrations is larger than anticipated.
- Samples were lost, did not pass analytical QA/QC, or were otherwise unavailable for inclusion in the analysis.
For more information on the MARSSIM process, visit MARSSIM on EPA.gov.