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HYDROLOGY OF THE PROPOSED PORTAL BENCH • ORCHARD VALLEY MINE COLORADO WESTMORELAND, INC. 1.0 INTRODUCTION Colorado Westmoreland, Inc. proposes opening new portals for their underground coal mining operation located near Paonia, Colorado. The proposed portals will be located on a cut and fill bench in the drainage of East Roatcap Creek. The proposed bench will fill the stream bed and, therefore, a culvert has to be constructed. Additional hydrologic structures will include perimeter and bench ditches and a sedimentation pond. Hydrogeologic investigation indicated that the proposed cut will not reach the depth of saturation in the colluvial and bedrock water bearing strata. However, during entry driving the saturated portion of the "D" coal seam will be reached. This report presents the results of hydrologic studies performed at the proposed construction site. • 2.0 SURFACE WATER HYDROLOGY 2.1 Regional hydrology General surface water hydrology in the region is described in detail in the Colorado Westmoreland, Inc. "Application for Permit for Surface or Underground Mining Activities - Minimum Requirements for Information on Environmental Resources", revised August 1, 1984, Section 2.04.7 Hydrology Description - (2) (a) (b) Surface Water Information, p 43 - 47. 2.2 Regional Climatology Temperature and precipitation data recorded in the period from 1957 to 1974 at Paonia, Colorado indicate the average daily temperature in the area to be 48.9° F. ;The average daily maximum temperature is 64.1° F and the average daily minimum temperature is 33.7° F. Average annual precipitation is 15.49 inches and the average snowfall is 50.7 inches (SCS, 1981). Average annual precipitation at the bench portal site was estimated from the U.S.G.S. map entitled Colorado Average Annual Precipitation 1951- 1980 (U.S.G.S., 1984) as 22 inches. 2.3 Local Drainage System Characteristics and Hydrology • 2.3.1 East Roatcap Creek The project site is located within the East Roatcap Creek drainage basin, a tributary of Roatcap Creek. Roatcap Creek is 1