2001-07-16_GENERAL DOCUMENTS - C1980007

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intermountain diversion and reservoir system will not be approved until an appropriate subsidence control plan is submitted and approved. One of the locations for alluvial deposits within the life-of-mine permit area is a 90-acre tract of land on the Dry Fork, immediately above Minnesota Reservoir. These alluvial deposits range from 100 to 300 feet in width. The valley floor above the reservoir widens and there is a definite break in slope from the steep sides confining the valley floor. Numerous beaver ponds and willow thickets occupy the valley floor in this location, and grazing is limited to isolated locations along the margins of the valley. The soils in this location are primarily deep clays. The Haplaquoll soil predominates. It is associated with beaver activity and commonly exhibits mottled conditions in subsurface horizons. The alluvial origin of this material is plausible because of the beaver activity and downstream channel blockage from a landslide and from Minnesota Reservoir dam which was placed at the blockage point. Normally the soil is saturated with water at or near the surface. Because of absence of the good aeration, organic matter content is high. The applicant states that the valley floor in this reach of the Dry Fork would be incapable of supporting agricultural activities without proper drainage. Approximately 20 percent of the total alluvial fill deposits above Minnesota Reservoir have an artificially high water table as a result of backwater conditions from the reservoir pool. This area could not be drained adequately without removing the reservoir. Even with adequate drainage on the remaining 72 acres, the agricultural development would be restricted to grasses and pasture because of the high elevations and short growing season. Furthermore, the beaver ponds and willow thickets are an important factor in the general ecological picture, since they help regulate stream flow, provide water for domestic animals and wildlife, and provide wildlife cover. A letter from the Delta Soil Conservation District dated February 17, 1981 indicates that agronomic development in this 90-acre tract is doubtful. During the periods 1950-62, 1964-70, 1972-1974, and 1977, water yields from the Deep Creek diversion canal were greater than releases from Minnesota Reservoir. During water years 1978, 1979, and 1990, all water passing through the Deep Creek Ditch into Minnesota Reservoir was released from the reservoir. Assuming no seepage and transmission losses, contributions of Deep Creek Ditch flow releases from Minnesota Reservoir ranged from only 13.5 percent to 25.4 percent between 1978 and 1980. It is assumed that seepage and transmission losses in the diversion canal result in a Deep Creek Ditch yield of less than 80 percent. The applicant has stated that the records of water yield from Minnesota Reservoir are not reliable and that there is no way to develop a meaningful comparison between the Deep Creek Ditch yield and the Minnesota Reservoir yield. As a result, it is difficult to assess the quantity and frequency of "natural" water supporting alluvial functions in the 90-acre tract immediately above Minnesota Reservoir. It is conceivable that the 61