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002835 Paper presented at: Conference on Water for Energy Development, Engineering Foundation, Asilomar Conference Grounds, Pacific Grove, California, December 5-10, 1976 SURFACE-WATER QUALITY IN THE YAMPA RIVER BASIN, COLORADO AND WYOMING--AN AREA OF ACCELERATED COAL DEVELOPMENT Dennis A. Wentz and Timothy Doak Steele U.S. Geological Survey Lakewood, Colorado ABSTRACT Coal production in the Yampa River basin of Colorado and Wyoming is ex- pected to exceed 20 million tons (18 million tonnes) annually by 1990. In- creased coal production and related development could increase withdrawals of surface water, which currently (1976) supplies the bulk of water used in the basin. t Analyses have been carried out to determine ambient surface-water qual- ity in the basin prior to accelerated coal-resource development. Regional temperature patterns, sediment yields, and relations between specific con- ductance and concentrations of major inorganic chemical constituents have been determined from available historical data. Time-trend analyses of his- storical stream temperatures at the mouths of the two main subbasins show no discernible changes since 1951. Over the same period, there has been a 14- percent increase in dissolved-solids concentration in one subbasin, although no change has occurred in the other. . The historical data were complemented by a reconnaissance of 82 stream sites in the Yampa River basin during low-flow conditions in August and Sep- tember 1975. At three sites, trace elements in water and in bottom sediments were found at anomalously high concentrations (concentrations that were high- er than ambient levels determined for the basin). Iron and manganese concen- trations exceeded current drinking water standards recommended by the U.S. Public Health Service (1962) at 40 sites in the basin; high concentrations of nitrogen, phosphorous, and organic carbon were found at six sites. Diversity indices for benthic macro invertebrates provide no concrete evidence for addi- tional anomalous sites in the basin. - A quarterly sampling program has been established at 30 of the 82 recon- naissance sites in order to assess seasonal variability. In addition, an on- going sediment-sampling program will provide information on areal sediment yields. These and other data will be used, along with various modeling tech- niques, to evaluate ambient water-quality conditions and to assess projected impacts on water resources of alternative coal-resource development plans in the basin. . 1