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(1977) contains ground-water reconnaissance and well-inventory information for the Uncompahgre Project (Lower Gunnison Basin Unit). The report also has some water-quality data, including data for arsenic and boron concentrations in ground water. Information about land and water resources, the irrigation system, water quality, and hydrogeology for the Uncompahgre Project is in two BOR reports (1982,1984). Hydrogeologic investigations related to irrigation in the Grand VaI]ey were reported in three BOR reports (1978, 1986a, b). The report from 1978 describes a detailed hydrogeologic investigation of the Reed Wash Basin for the Stage One salinity project. Geo]ogic logs and salt-loading infonnation for the cobble aquifer in the Grand Valley are in a BOR report (1986a). Studies have been done since the early] 980's concerning threatened and endangered fish species in the Upper Colorado River Basin, and part of that work was done in the Grand Valley area. Most of the studies in the Grand Valley area concerned the Colorado River squawfish and the razorback Sucker. Behnke and Benson (1983) and Archer and others (1985) described population, habitat, and reservoir effects on endangered fish in the Upper Colorado River Basin. A study of bony tail chub was described in Kaeding and others (1986), and a study of Colorado squawfish and razorback suckers in a reach of the Colorado River in the Grand Valley was described by Osmundson and Kaeding (1989). Concentrations of trace constituents in Colorado squawfish were described by Krueger (1988). Concentrations of organochlorine pesticides and trace constituents in endangered fish were described in Kurey (]985a, b). Acknowledgments The authors thank the numerous property owners for allowing access to their property for collec- tion of samples. We also thank Jack Cunningham and Kenneth Weston (BOR) for compilation of historical ground-water and aquifer-test data, Roger Fujii (USGS) for selenium-speciation analysis and for his insights concerning selenium geochemistry, David Wo]ny for his interpretation and valuable infonnation on the local geology, and Jeffery Foster (USGS) for assistance with collection of surface- water and ground-water data. The authors also thank Larry Fukui of RUST Geotech, Inc., in Grand Junction, Co]o., for mineralogic analysis, and Dorothy Hahn and Carol Bums for assistance With biota sampling and data compilation. Bioassay tesls on water and bottom sediment were done with the help of the following employees of the U.S. Environmental Protection Agency: Loys Parrish and Bill Schroeder in Denver, Colo., and Mark Smith in Cincinnati, OMo. SOILS AND ALFALFA INVESTIGATIONS An unbalanced, four-level, stratified random sampling design was used to define sources, distribu- tion, and variability of selenium and other trace- constituent concentrations in the soils and associated a1fa]fa among and within geologic units in the Uncompahgre Project area. As part of the soil- sampling scheme, geologic units were mapped and described based on earlier geologic maps and soil- survey maps of the project area (Marshal], ] 959; Williams, ]964; Cline and others, 1967; Tweto and others, 1976; Steven and Hail, 1989). Soils derived from five geologic units were sampled: Upper Cretaceous Dakota Sandstone (Kd); Upper Cretaceous Mancos Shale (Km); Quaternary deposits in ancient terraces and alluvial fans (Qt); Quaternary (Ho]ocene) a1]uvium overlying Mancos Shale (Qm); and Quaternary (recent) flood-plain alluvium deposited by the Uncompahgre River and other streams (Qr). In the Uncompahgre Project area, most of the soils of unit Qm were derived from Mancos Shale. One site was sampled on Quaternary alluvium derived from Dakota Sandstone (Qd). Fifteen townships were included in the study area, and the distribution of soil-sampling sites is shown in figure 6. All soil samples were collected in irrigated areas. Random sections were selected in each township until all geologic units in a township had been selected, in triplicate, for soil and alfalfa sampling (fig. 6). The sample distributions by geologic unit from the randomly selected sections are listed in table I. Township 4 had four sites for the geologic unit Km; geologic unit Qd was sampled only in township] 3 (table I). If a preselected site was unacceptable in the field because of irrigation or absence of alfalfa, a new site was selected in an adjacent section as close as possible to the original site. To assess variability within a section, two samples about 100m apart were collected in ]4 randomly selected sections. 16 Detatted Study 01 Selenium end Other Conelltuenta In Weter, Boftom Sediment, Sott, ARalia, and Biota Aoooclated with IrrlgoUon Drainage In the Uncompahgre Project Area and In the Grand Vattey, Weot-<:antral Colorado, 1991-93