2015-10-06_PERMIT FILE - C1981019A (2)

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RULE 2 PERMITS The flooding and mass -wasting event of 1983-1984 downcut the valley fill as much as 20 to 30 feet below the former surface in some locations. The resulting lowering of the valley fill groundwater table was noted by Tetra Tech as having caused drying of former wetlands and colonization by upland plant species. Remaining wetlands are generally associated with springs and seeps issuing from perched water in bedrock along the valley wall. Examination of non -wetland soil profiles next to drainages revealed very few soils with mottles, shallow rooting depth, or other characteristics indicative of subirrigation. Suitability for Flood Irrigation Since 1974, Colowyo and other private and governmental groups have collected samples of water flows and water quality in the area. Water of sufficient quality and quantity for seasonal flood irrigation does exist in some areas (WMC 2005). However, the cost to develop such an irrigation system would be prohibitive given the remote location and limited area available for irrigation (Dames and Moore 1980, Walsh 1984). New irrigation projects are very rare in local agricultural practice, and would incorporate sprinkler irrigation rather than inefficient flood irrigation. Conclusion Tetra Tech's 2005 report presented the following findings regarding the presence of alluvial valley floors in the Collom permit expansion area: • Alluvial materials are present in the valley bottoms of the Collom Gulch, Little Collom Gulch, and Jubb Creek drainages, but the materials are intermixed with significant fractions of colluvium and sheetwash from adjacent slopes. • Based on depth to groundwater, subirrigation within these valley bottoms is very limited. • Active erosion in the stream channels is causing further incision, lowering of the groundwater table, and reduced flood frequency, reducing the ability of the valley bottoms to support any agricultural use other than rangeland. • Local and regional agricultural economics are prohibitive to developing irrigation projects within these valley bottoms, and such practices are in decline locally, especially on such a small scale as would be required by the narrow and fragmented nature of irrigable bottomlands within the subject drainages. The narrow width and fragmented nature of the minimal flat land, depth to ground water, and impracticality of economically irrigating or mechanically farming the valley bottoms within Collom Gulch, Little Collom Gulch, and West Fork of Jubb Creek indicate that those drainages do not qualify as alluvial valley floors. The same conclusions may be reached for the area of proposed disturbance for construction of the Collom Haul Road in the vicinity of the Gossard Loadout Facility (Map 25E Sheet 5 of 10): Alluvial materials are present in the valley bottom of the Gossard Loadout complex, and lower reaches of the Lower Wilson drainage, but the materials are intermixed with significant fractions of colluvium and sheetwash from adjacent slopes and the mass wasting event experienced in 1983-1984. Based on an average depth to groundwater of approximately 21 feet for the existing alluvial groundwater well know as "Gossard Well" (2009 Annual Reclamation Report) since 1983, subirrigation within this valley bottom is very limited. Monitoring well MW -95-02, located in the area hydrologically above the proposed road corridor portrays similar depth to water Collom— Rule 2, Page 146 Revision Date: 6/15/15 Revision No.: TR -106