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Mountain Coa! Company 1999 Mnual Hydrology Report West Elk Mine • Introduction Purpose The purpose of this 1999 Annual Hydrology Report (AHR) is to summazize Mountain Coal Company's (MCC) hydrologic monitoring activities at the West Elk Mine; report the results of these monitoring activities; and describe the significance of the data, particulazly with respect to mining activities as they relate to the Probable Hydrologic Consequences predictions. Overview of 1999 Mining Activities Longwall Mining During water year 1999 (WY99), mining was completed in the western halves of Longwall panels 12 and 13 (Map 1). By the end of the water yeaz, the Longwall had advanced to 27 cross-cut in Longwall panel 13. Development Mining Development continued north in the Box Canyon Mains and development of Longwall panel 13A during WY99 (Map 1). Development in the 14 Tailgate and Headgate proceeded cautiously after the 14SEHG fault was encountered. • Hydrologic Characterization of 1999 Water Year Water Year 1999 (WY99) was characterized by below average snowfall at the higher elevations, which resulted in below average streamflows in the North Fork of the Gunnison River and in Minnesota Creek. WY99 precipitation (measured in Paonia) was slightly above the 30-year average yet varied substantially from month to month in comparison to the historic data. February and March precipitation totals were less than 40% of the long-term monthly averages while Apri] and July were 200% and 240% respectively of the long-term monthly averages. Climatological Data To summarize precipitation information for the West Elk Mine, data were used from the Paonia, McClure Pass, and Overland Reservoir monitoring stations. Snow data, as well as overall precipitation for WY99, were compared to long-term averages for these stations to categorize the extent to which the weather deviated from normal. For precipitation data, Climatological Data for Colorado, published by the National Oceanic and Atmospheric Administration were used, and for the snow data, snow station data from the Natural Resources Conservation Service SNOTEL information database were used. Total precipitation measured at the Paonia I SW station for WY99 was 108 percent of normal - defined by the 30-yeaz average (1961-1990). Not counting the wet months of April and July, precipitation during the remaining ten months was at 88 percent of the 30-year average. For WY99, snowpack was only 65 percent of the average at the McClure Pass Station, and 75 • 831-03?.520 Pagel {4}fight !4'ater Engineers