2009-02-10_PERMIT FILE - C1981022 (5)

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Semis: - 2.04.7 spruce/subalpine fir and Douglas fir forest interspersed with mountain meadow at the higher • elevations, and mixed shrub and pinon-juniper dominating the steep lower slopes. The surface hydrologic environment in the immediate mine area is a direct reflection of site topography, the locally semi-arid climate, and site geology. The North Fork of the Gunnison River is the major drainage in the area flowing from northeast to southwest along the margins of the Grand Mesa monocline to the north and the West Elk Mountain uplift to the south. Tributary drainages on either side of the North Fork Valley are relatively steep and deeply incised. Topography in the mine permit and adjacent areas is graphically illustrated by the Regional Geology/Hydrology Map, (Map 2.04-M2). The semi-arid climate limits overall precipitation and there is significant variation in precipitation between the lowland valley areas to the west (approximately 5 inches per year) and the high mountain peaks to the east (approximately 20 inches per year). Average annual precipitation in the immediate mine vicinity is approximately 16.9 inches per year. Because it is relatively dry, most of the precipitation which does occur infiltrates quickly into the relatively coarse, unconsolidated surface materials and is rapidly lost to evaporation and transpiration. Very little runoff occurs except during spring snowmek and major thunderstorm events, and what little runoff does occur results in brief, high flow velocities in the smaller drainages due to the steep terrain. Downstream flows in the North Fork can also vary significantly during irrigation season due to significant irrigation withdrawals. The only drainages which have a perennial flow pattern are those with relatively large watershed areas and numerous tributaries, while many of the smaller ephemeral drainages flow rarely, if at all. High flow velocities are often accompanied by relatively high sediment loads. The intermittent high- velocity flows limit sediment deposition in the upper drainage reaches but result in significant sediment deposition in lower valley areas to the west where flow gradients flatten. The steep valley • sideslopes and extensive exposures of to* cliffs, which dominate the area, contribute to significant deposits of large, blocky colluvial material on the lower valley slopes and in most area drainages. Potentially Affected Surface Water Drainages and Drainage Characteristics - Potentially affected surface drainages include the North Fork of the Gunnison River, as the primary receiving drainage, and the following small perennial, intermittent, and ephemeral tributaries, listed in sequence from east to west: • Thompson Creek (intermittent) • Baniine Canyon (ephemeral) • Hoopla Gulch (ephemeral) • Hawk's Nest Creek (ephemeral) • C Gulch (ephemeral) • B-Gulch (ephemeral) • A-Gulch (ephemeral) • Coal Gulch (ephemeral) • Unnamed Drainage (ephemeral) • Sanbom Creek (ephemeral) • Elk Creek (intermittent) • West Valley Drainage (ephemeral) • West Valley2 Drainage (ephemeral) • Bear Creek (ephemeral) • Hubbard Creek (perennial) These drainages are shown on the Surface Water Hydrology Map, (Map 2.04-M6), and described in the following sections. PR04 2.04-53 Revised August 2000