3.3.10 Decision Units for Very Large Areas

The investigation of hundreds or even thousands of acres of land for potential contamination can be logistically and financially challenging. DU designation should be based on the CSM. Areas of suspected heavy contamination should be investigated separately from areas of different historical use, and soil types and other factors should also be considered when distinguishing separate areas. Nevertheless, some areas for which a decision will be made may be so large that it would require an enormous number of individual DUs for complete coverage at an appropriate and useful scale. In these cases, sampling each DU may not be economically feasible. Sampling only a fraction of the area as SUs and extrapolating those results to make a decision regarding the DU will undoubtedly be attractive from a cost and logistical standpoint. However, this approach introduces additional uncertainty into the evaluation that may or may not be acceptable in achieving site objectives. Tradeoffs between economic feasibility and management of uncertainty must be considered when developing DUs for very large areas (see Sections 4 and 7). However, recall that decision mechanisms involving extrapolation are not acceptable to regulators in some states.