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I • • POWDERHORN COAL, COMPANY 1991 ANNUAL HYDROLOGIC REPORT OCTOBER 1, 1990 THROUGH SEPTEMBER 30, 1991 INTRODUCTION Operations continued at Powderhorn's Roadside Mine during the 1991 water year with a production of 210,929 clean tons. The Cameo No. 1 Mine was idle during this period. There were no changes in hydrologic monitoring methods during the year. SURFACE WATER For the fifth year in a row the total flow in the Colorado River was below the normal. The following is flow in the river for the past 6 years as recorded by the USGS at station 09095500 which is located a couple of miles up stream from the mines: Water Year Total Acre-feet 1934-1991 2,821,000 1986 4,156,000* 1987 2,596,000 1988 2,154,000 1989 1,859,000 1990 1,643,000 1991 2,174,000 $ of 1934-1991 Ave. 100 147 92$ 76~ 66$ 58~ 77~ *Previously reported in error as 9,156,000 back to the 1987 AHR. Approximately 1.39 million tons of dissolved solids flowed past this USGS station during the 1991 water year. This figure was calculated using the monthly mass average conductance of 675 umhos/cm and a conductance/TDS ratio of 1.43 calculated for the river in an earlier AHR. Measured flows in Cottonwood Creek and Rapid Creek were generally lower than normal. Tables 591-1 through 591-4 show the average daily flow for periods when recorders were in place and operating. The flows in the flumes at locations SWGS-O1 and SWGS-02 were below the recording level of the recorders most of the summer. The flows at location SWGS-03 were higher than the previous two years and were closer to normal flow. Correlation between the upper flumes, 002 and 003, and their combined flow at the lower flume, 001, is nearly impossible. The City of Palisade can control the flows relative to the needs of their domestic water supply system and irrigation water is removed at various locations depending upon the call for water.