4. STATISTICAL SAMPLING DESIGNS FOR ISM

This section summarizes results of simulation studies used to evaluate the performance of ISM in estimating the mean under various conditions. Conclusions from these studies are discussed, and recommendations for ISM sampling based on this evaluation are presented in Figure 4-1. The recommendations for ISM sampling design, number of increments, and number of replicates as shown in Figure 4-1 come from the simulation studies discussed in this section and presented in more detail in Appendix A.

As mentioned in Section 3, a variety of sampling designs should be considered during systematic planning. To determine which will fully meet the project objectives most efficiently, it is necessary to have some idea of how many samples will be required as part of the design. Figure 4-1 provides guidance on the number of increments and replicates to collect within a DU if incremental sampling is selected as a sampling strategy. Within each DU, the pattern for spatial collection of the increments is not specified in this figure but is discussed in Section 4.3. Methods for estimating the mean concentration present at the site based on incremental samples (as depicted in the ovals in this figure) are also not presented in this figure but are discussed in detail in Section 4.2.

After data are collected and reviewed, it is important to revisit the outcomes of the systematic planning process to ensure that the data meet the project objectives. The guidance offered in Figure 4-1 is meant as general guidance for the number of replicates and increments necessary to achieve particular objectives. These recommendations are likely to provide sufficient information to meet most basic objectives relating to comparison of an estimated mean or UCL for the mean to a decision threshold. However, the project team must consider whether or not the project objectives have been fully satisfied by the data collected. If the data are not satisfactory for decision making, further consideration and revision of the systematic planning process and outcomes are necessary.