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Water Replacement Plan 12 /27 /63 Page Three Streams All but major streams in the area are of intermittent or ephemeral character. The monitoring information is contained within the specific basin data, The description of each stream is contained within that specific basin information. For more information on the surface hydrology of the area, please see Section 2.04.7 of the Orchard Valley Mine Underground Mining and Reclamation Permit. GROUNDWATER HYDROLOGY The three categories of potential aquifers within the area are: 1. North Fork of the Gunnison River alluvium and its associated terrace deposits. 2. Localized shallow alluvial areas in drainage basins. 3. Groundwater in the Mesa Verde formation. The most important alluvium in the mine operation area is that of the North Fork of the Gunnison River, which, at its closest point is approximately twa miles from the mine mouth and 1500 ft, lower in elevation. Significant amounts of sand and gravel alluvium exist along the North Fork of the Gunnison from the mouth of Terror Creek to the confluence of the Gunnison River. Because of its location, the North Fork of the Gunnison River alluvium will be not be impacted by underground mining. For more information, see Section 2.04.7(1)(a) Orchard Valley Mine Underground Mining and Reclamation Permit. Generally, because of the geomorphology of the area, the streams within the area have very shallow alluvium and litt]e groundwater except during periods of stream flow. Each stream alluvium will be described in detail within the specific information. The Orchard Valley Mine is located on an outcrop of the Mesaverde formation, which is a thick series of interbed sandstones and shales which form the middle slopes of the hillside north of the North Fork of the Gunnison River. Strati- graphically, the Mesaverde formation is above the Mancos shale and below the Wasatch formation. Colorado Westmoreland Inc. has undertaken an extensive core hole drilling program in the area for the purpose of developing bedrock ground- water information. Because of the dip of the Mesaverde formation and the collu- vial sources of the springs within the area, it has been determined that the colluvial springs are not part of a deep aquifer system. More information may be found in Section 2.04.7(1)(a) Orchard Valley Mine Underground Mining and Reclama- tion Permit and United States Geological Survey Water Resources, Investigation Report 83-4069.