What are the limitations of composite sampling?
Preliminary discrete samples and/or site history details are necessary to demonstrate that the media meets the requirements and to derive adjusted benchmarks. The resulting information on contaminant extremes and variability in the media or biota is reduced upon compositing. Composites may mask hot spots if benchmarks are not adjusted to account for the number of component samples per composite and the known/expected variability. For example, to achieve 91% detection probability of hot spots of 3 ppb with a discrete sample criterion of 1 ppb, the adjusted benchmark for 4 discrete samples per composite is 1.05 ppb, while for 8 discrete samples it is 0.8 ppb. Using an adjusted benchmark of 1.05 ppb with 8 discrete samples per composite would lower the detection probability to 64%. Some of the statistical approaches to deriving the appropriate number of components and adjusted benchmarks are complex and time consuming. Valid methods for adjusting the benchmarks are limited to single conta
