[en] Environmental sampling and monitoring of the area downwind of a nuclear power plant is required in the event of an accidental release of radioactive materials. Typically, radiation monitoring teams would be deployed to make instrument measurements at selected offsite locations downwind from the release point. The objective is to (1) locate the plume front, edges, and centerline, (2) make periodic measurements of airborne concentrations of noble gases, radioiodine, and radioactive particulates, and (3) collect samples of soil, vegetation, and water in the ingestion exposure pathway to determine environmental radiation levels. Such observations help to establish an exposure rate pattern useful for protecting the population in the anticipated path of the radioactive plume. Current source term research suggests that only noble gases will be present in all but the most severe accidents. Thus, it is important for environmental monitoring teams to be well-trained in noble gas plume monitoring techniques. Specific techniques for identifying elevated and ground level plumes and for defining plume edges, centerline, and width will be discussed. The dynamics of plume behavior in the environment will also be discussed. The differences between idealized meteorological data in exercise scenarios and real meteorological data will be emphasized. The impact of real meteorological conditions on environmental radiation measurements and the comparison or understanding of measurement results will be described. 14 references