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POMDERHORN COAL COMPANY • 1987 ANNUAL HYDROLOGIC REPORT OCTOBER 1, 1986 THROUGH SEPTEMBER 30, 1987 INTRODUCTION This year's annual hydrologic report covers the 1987 water year, October 1, 1986 through September 30, 1987. The information submitted for October 1, 1986 through December 31, 1986 which was in the 1986 Annual Hydrologic Report has been repeated in this report to make the year complete. The mine inflows studies in this report were taken in October and November 1987. The Roadside and Cameo Mines went into temporary cessation in October 1986 and continued in that status through the end of the water year. Whether or not active mining will resume in 1988 has not been determined. Revisions to the hydrologic monitoring schedule were made by TR-04 in November 1986 and additional revisions were requested in the permit renewal application submitted June 30, 1987. The permit renewal was approved in January 1988. SURFACE MATER MONITORING The results of monitoring on the Colorado River during the 1987 water year are • shown on data, pages SB-1 and SB-2. The flows shown on the Upper Colorado River were taken from the daily average flows recorded by the USGS at Station 955. The following is the total flow at Station 955 for the last four years: Mater Year Total Acre-Feet 84 5,521,000 85 4,304,000 86 4 9:156,000 87 2,596,000 1933-1978 Ave. 2,752,000 The 1987 flow was 94% of the average flow but only 47-62% of the previous three year's flows. Using the USGS monthly average conductivity and flows for the year, a mass average conductivity of 737 ~anhos/cm was calculated. Approximately 1.82 million tons of TDS were carried past the USGS Station 955 in 1987. The flow monitoring continued on Rapid and Cottonwood Creeks but at a reduced rate. Lower Rapid Creek, SWSG-01, monitoring is required continuously year round when not frozen. Upper Rapid Creek, SWGS-03, .and Cottonwood Creek, SWGS-02, monitoring is required bimonthly in June through November, Since recorders were still in place on SWGS-02 and 03, monitoring was done continuously, The gaps in information caused by expired clocks and mechanical problems were reduced in 1987. Gaps in previous information make comparison of data difficult. Tables 586-11 and 12 and S87-1 thru 5 contain the data. collected during the water year (there was no data in December 1986). The daily values are an average of 4 • readings six hours apart. The data from these tables is shown graphically on Diagrams 586-5 and 587-1 thru 3. The following is a table of average daily flow for the months when stream flow is most critical for irrigation July - October: