2.6.2 Composite Sampling

A discussion of composite sampling goals and sample collection techniques may seem out of context in a description of ISM principles. However, as is noted in Section 8.2, there is a general misunderstanding that ISM is simply a new term for what many may already be familiar with as composite sampling. Therefore, some background on composite sampling from existing federal guidance is provided here together with potential beneficial and common misuses of this sampling strategy.

A number of guidance documents generated by USEPA and other organizations address the compositing of soil and other environmental media (USEPA 1985, 1986, 1989a, 1995b, 1996a, 1996b, 2002d, 2002e; Gerlach and Nocerino 2003). These documents provide many details for how to use compositing for different project purposes; however, important details on how to collect and process composite samples are generally not discussed in great detail in the existing USEPA guidance. A composite sample is defined by USEPA as a sample created by combining several distinct increments (Gerlach and Nocerino 2003). USEPA guidance frequently acknowledges that sampling error far outweighs analytical error and that soil sample "homogenization" is critical (USEPA 1995b). However, specific guidance for how to achieve relatively even distribution of contaminants throughout the sample via field and laboratory subsampling and processing procedures is not provided. An exception is the RCRA Waste Sampling Technical Guidance (USEPA 2002e). This document explains Gy theory and discusses various applications of composite sampling. USEPA guidance describes several compositing designs, each with a different purpose. One of those purposes is determining the mean over a DU.