The Incremental Sampling Methodology (ISM) document describes the principles and the approaches needed to ensure representative, reproducible, and defensible data during soil sampling. ISM involves planning, sample collection, and laboratory processing and analysis to provide a representative sample with results that more accurately reflect the mean concentration of the area of interest than discrete samples. The ISM document provides you the key principles regarding sampling and sampling error and how ISM reduces those errors so that you can have more confidence in your sampling results.
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An updated ITRC guidance (ISM-2) was developed and posted in the fall of 2020. The ISM-2 Update Team clarified inappropriate or inconsistent information in ISM-1 is as seen in the attached statement. Please review this document before downloading the ISM-1 PDF.
ISM is increasingly being used in the environmental field for sampling contaminants in soil. Proponents have found that the sampling density afforded by collecting many increments, together with the disciplined processing and subsampling of the combined increments, in most cases yields more consistent and reproducible results than those obtained by more traditional (i.e., discrete) sampling approaches.
In 2009, ITRC established a technical team to evaluate ISM for sampling soils at hazardous waste sites and potentially contaminated properties. The ISM Team convened national experts in fields such as toxicology, risk assessment, statistics, and soil sampling. This 2012 guidance analyzes ISM performance, identifies considerations for unique laboratory processes and procedures, evaluates the suitability of ISM to various contamination scenarios and contaminant categories, and identifies the strengths and weaknesses of ISM.