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1 002451 SIMULATED EFFECTS OF ANTICIPATED COAL MINING ON DISSOLVED SOLIDS IN SELECTED TRIBUTARIES OF THE YAMPA RIVER, NORTHWESTERN COLORADO By Randolph S. Parker and J. Michael Norris ABSTRACT Identifying cumulative effects of mining on dissolved solids downstream from multiple coal-mining operations is particularly important in western basins. The problem of identifying cumulative effects is evident in the Trout Creek drainage, a tributary to the Yampa River in northwestern Colorado, where a number of mines are active and expansions planned. As an evaluation tool, a model was developed and calibrated for the Trout Creek drainage and a reach of the Yampa River main stem. In the model a series of nodes on the stream network is used to sum water quantity and quality through the network. The model is operated on a monthly time step and was based on data from water years 1976 to 1981. Out- put is mean monthly discharge, dissolved-solids concentration, and dissolved- solids load. Observed data are needed to initiate the model and for model calibration. Some data were extrapolated from records of nearby streamflow- gaging stations. Some nodes within the stream network were inputs from anticipated m~n~ng and were inactive during calibration. After calibration, these nodes were used to input water discharge at a given dissolved-solids concentration to reflect various future mine configurations. INTRODUCTION The demand for energy in this Nation has fostered increased needs for coal. In response to this demand, one area of increased coal-mining activity is the Yampa River basin in northwestern Colorado. Many coal mines are now active in the basin, and many of the mining companies have proposed expansion of active coal mines or have identified sites for new mines. The Yampa River basin is hydrologically typical of many coal regions in Colorado. Much of the streamflow of the main stem of the Yampa River is derived from high-altitude mountain snowpacks. The geology of these high- altitude areas is very different from the geology of the coal areas in the basin. The basic rock types in the high-altitude areas are igneous and meta- morphic and result in streamflow with low dissolved-solids concentration. Coal mines are located in sedimentary-rock areas which may yield higher dissolved solids.