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XVII. Operations on Alluvial Valley Floors 1. Unconsolidated streamlaid deposits holding streams have been identified within the proposed permit and adjacent areas, and are shown on Map 4a, Mine No. 3 Hydrology. As shown on the map, three areas are acknowledged by the applicant as meeting the geomorphic criteria of alluvial valley floors. These areas are: 11 the flood plain of fish Creek; 21 the flood plain of Middle Creek downstream from U.S.G.S. Gaging Station 09243700; and, 3) the flood plain of Foidel Creek downstream from U.S.G.S. Gaging Station 09243900. The flood plain of Fish Creek does not lie within the boundary of the proposed permit area and would not be affected by the proposed mining and reclamation operations as described in this application. Therefore, this area will not be considered further. Areas of unconsolidated streamlaid deposits along Foidel Creek and Middle Creek that are located geographically adjacent to surface facilities areas and proposed mining and reclamation operations could potentially be affected. The applicant's discussion of probable hydrologic consequences indicates that discharge from the mine detention basins is expected to increase the dissolved salt load of streams draining the permit area. Since water from the Foidel Creek and Middle Creek stream/alluvial systems drains to the lower reach of Trout Creek, these three areas must be considered in the alluvial valley floor determination. 2. Alluvial Valley Floor Determination Map No. 8 of the permit application shows that flood irrigation exists within and adjacent to Specifically, the Lieske, Connel and Homestead derive their water from Trout, Middle and Foid~ currently used, or have been historically used floodplains. the capability for the permit area. Ditch systems, which ~1 Creeks, are to irrigate these In order to evaluate the potential for subirrigation within the proposed permit and adjacent area, the applicant conducted a study on subirrigation capability in the floodplains of Foidel and Middle Creeks. Based on this study, the applicant found that subirrigation does not occur along lower Foidel or Middle Creek. The study was conducted in October, 1980. The Division does not feel that the study is representative of the entire growing season. Therefore, the results of this study reported in the permit application are not sufficient for the Division to conclude that subirrigation does not occur during a major portion of the growing season. Based on available information, the unconsolidated streamlaid deposits of Lower Foidel, Middle and Trout Creeks are found to be alluvial valley floors because of the current or historical existence of flood irrigation and the presumed capability of these areas to support subirrigation during a portion of the growing season. -36-