2 and 3 scores cluster shown in figure 3A . With the exception of the Riverton Reclamation Project, Tulare Lake Bed Area, and Salton Sea Area, all study areas have irrigated soils developed on upper Cretaceous marine sediments. Once constructed, the classification model can be used to determine the selenium-producing potential of areas with unknown or poorly known selenium concentrations in water samples. Data from Wyoming and Utah were selected because of the diverse geologic environments represented in these areas and the documented presence of selenium in surface-water samples. More than 80 percent of the samples with low selenium concentrations were correctly classified into groups 2 or 3.
Numerous circumstances contribute to the lack of selenium data for water samples.
Stewart Lake is the Middle Green River Basin, Utah, study area. The following publications contain additional information on the occurrence of selenium in irrigation drainwater and the geochemical and statistical tools used to identify and predict the occurrence of selenium-producing landscapes. Help in using USGS pages.