Role of laboratory sampling devices and laboratory subsampling methods in representative sampling strategies

Sampling is the act of selecting items from a specified population in order to estimate the parameters of that population (e.g., selecting soil samples to characterize the properties at an environmental site). Sampling occurs at various levels and times throughout an environmental site characterization process. Typically, initial (primary) sampling occurs in the field while subsequent stages of sample size reduction (subsampling) occur until the final laboratory analysis stage. At each step in the measurement process, from planning, site selection. sample collection, sample preparation, through sample analysis, errors can occur that propagate, leading to uncertainty associated with the final result upon which decisions will ultimately be made. The goal of all sampling efforts should be to select samples that are representative of the population (i.e., site) in question. General guidelines, with supporting background and theory, for obtaining representative subsamples for the laboratory analysis of particulate materials using "correct" sampling practices and "correct" sampling devices are presented ("correct" as defined by Gy sampling theory; see Pitard, 1993). Considerations are given to: the constitution and the degree of heterogeneity of the material being sampled, the methods used for sample collection (including what proper tools to use), what it is that the sample is supposed to represent, the mass of the sample needed to be representative, and the bounds of what "representative" actually means.