The elements of ISM that control data variability are incorporated into (a) the field collection of soil samples and (b) laboratory processing and subsampling procedures.
Incremental sampling methodology (ISM) is a structured composite sampling and processing protocol having specific elements designed to reduce data variability and increase sample representativeness for a specified volume of soil under investigation. Variability in measured contaminant concentrations between discrete soil samples is due primarily to the particulate nature of soil and heterogeneity in the distribution of contaminants. The elements of ISM that control data variability are incorporated into (a) the field collection of soil samples and (b) laboratory processing and subsampling procedures. ISM is designed to obtain a single aliquot for analysis that has all constituents in the same proportion as an explicitly defined area/ volume of soil. Properly executed, the methodology provides reasonably unbiased, reproducible estimates of the mean concentration of analytes in the specified volume of soil.
In 2009, the ITRC convened the ISM Team to prepare this guidance document, which focuses on soil sampling. ISM addresses all the sources of sampling error in a systematic fashion (Gy 1998, Smith 2006). Other approaches to soil sampling have not emphasized reducing sampling error as much as ISM. Because this methodology requires change from traditional approaches, the ISM Team found it necessary to go into detail about the theory as well as the application of incremental sampling. The team found this to be a valuable exercise and it should be valuable to the reader as well. Because a good deal of new terminology is introduced by ISM, the reader is directed to the glossary in Appendix E. Section 1.8 also illustrates some key terms used in this document.
The ISM Team recommends that, as with any well-conceived sampling approach or plan, all members of the investigation project team (e.g., consultants, regulators, geologist, analytical chemists, risk assessors and toxicologists) be involved in the entire ISM development process.