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Incremental Sampling Methodology
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The ITRC Incremental Sampling Methodology (ISM) Team was created in 2009 to develop guidance for the appropriate implementation of incremental sampling for a wide range of sampling objectives, analytes, and circumstances.
Incremental sampling is a structured sampling protocol that reduces data variability and increases sample representativeness. US EPA Method 8330B for explosive compounds recommends the use of ISM in both field sample collection and laboratory subsampling to address the aforementioned problems. However, the specific protocols developed for 8330B are not necessarily directly transferable to other soil investigations having different sampling objectives or analytes of interest.
The objective of incremental sampling is to obtain a single sample for analysis that has an analyte concentration representative of the decision unit. ISM improves the reliability and defensibility of sampling data by reducing variability when compared to conventional discrete sampling strategies. The data distribution for ISM replicate samples tends to be normally distributed, as contrasted to the positively skewed distribution seen with discrete samples. Fewer nondetect results can be expected using ISM, thus mitigating problems caused by using censored data sets and lessening the chance of missing significant contamination. In addition, levels of statistical confidence and decision uncertainty that would require a large number of discrete analyses can often be obtained with a few incremental samples.
The foremost product of the ISM Team was the development of a formal ITRC technical and regulatory guidance document “Incremental Sampling Methodology (ISM-1)”. The document provides users with a practical working knowledge of the concepts and principles of the methodology, emphasize the critical importance of clearly articulated sampling objectives, and provide a sound basis for adapting ISM to meet project goals and site-specific objectives. The guidance document helps avoid misapplication of the approach, correct some common misperceptions, and address regulatory concerns.
The ISM Team developed a website for its work products, which will also serve as a central repository for related literature and references. The team also compiled a list of ISM potential advantages and pitfalls, including case studies illustrating both good examples and “lessons learned.” Cost information will be included when available. Internet-based training based on the technical and regulatory document has also been developed.