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RULE 2 PERMITS <br />Flood Irrigation and Agricultural Activities <br />Section 2.04.3 contains a description and map of agricultural activities in the permit and adjacent area. <br />The Premining and Postmining Land Use Map (Map 17) shows that the historic pre -mining land use of <br />the area has been generally undeveloped rangeland. Exceptions to undeveloped range land in the permit <br />area include the presence of equipment staging areas, small structures, reservoirs, roads, and stream <br />crossings. However, documentation exists indicating several small parcels along the West Fork of Jubb <br />Creek, totaling approximately 24 acres, were historically used for hay production. No evidence of any <br />irrigation for these parcels was found. <br />Historically, there has not been a developed water supply for agricultural activities in the potentially - <br />affected drainages. In addition, based on field investigations, there is no evidence of historical flood <br />irrigation in the Collom permit expansion area. <br />Subirrigation <br />Depths to groundwater in the valley fill materials in the Collom Mine Expansion area have been recorded <br />as between 9 feet below ground surface (bgs) along West Fork Jubb Creek (near a small pond), to greater <br />than 47 feet bgs within Little Collom Gulch. Further information on groundwater occurrence is provided <br />in Section 2.04.7. <br />The effects of the mass -wasting event of 1983-1984 downcut the valley fill throughout this area as much <br />as 20 to 30 feet below the former surface in some locations. The resulting lowering of the valley fill <br />groundwater table was noted by Tetra Tech as having caused drying of former wetlands and colonization <br />of the land by upland plant species. Remaining wetlands in the valley bottoms are generally associated <br />with springs and seeps issuing from perched water in bedrock along the valley wall. Examination of non - <br />wetland soil profiles next to drainages revealed very few soils with mottles, shallow rooting depth, or <br />other characteristics indicative of subirrigation. <br />Suitability for Flood Irrigation <br />Since 1974, Colowyo and other private and governmental groups have collected samples of water flows <br />and water quality in the area. Water of sufficient quality and quantity for seasonal flood irrigation does <br />exist in some areas (WMC 2005). However, the cost to develop such an irrigation system would be <br />prohibitive given the remote location and limited area available for irrigation (Dames and Moore 1980, <br />Walsh 1984). New irrigation projects are very rare in local agricultural practice, and would incorporate <br />sprinkler irrigation rather than inefficient flood irrigation. <br />Conclusion <br />Tetra Tech's 2005 report presented the following findings regarding the presence of alluvial valley floors <br />in the Collom permit expansion area: <br />Alluvial materials are present in the valley bottoms of the Collom Gulch, Little Collom Gulch, <br />and Jubb Creek drainages, but the materials are intermixed with significant fractions of colluvium <br />and sheetwash from adjacent slopes. <br />Based on depth to groundwater, subirrigation within these valley bottoms is very limited. <br />Active erosion in the stream channels is causing further incision, lowering of the groundwater <br />table, and reduced flood frequency, reducing the ability of the valley bottoms to support any <br />agricultural use other than rangeland. <br />Collom — Rule 2, Page 129 Revision Date: 1/6/17 <br />Revision No.: TR -109 <br />