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However, this area is not exempt from the requirements for restoring the essential hydrologic functions <br />of the alluvial valley floor, which will be discussed below, in Item 3. <br />All of the non - exempt alluvial valley floor is located outside the permit area within Section 26 and 27. <br />1. No portion of the non - exempt alluvial valley floor is presently disturbed by the mining operation. <br />A small portion of this area is indicated as being historically flood irrigated on Exhibit 33. There <br />are no plans to disturb any additional land on the alluvial valley floor. Therefore, the proposed <br />coal mining operation will not interrupt, discontinue, or preclude farming on the alluvial valley <br />floor (4.24.3(1)). <br />2. As previously discussed, a portion of the non - exempt alluvial valley floor was historically flood <br />irrigated. In addition, a portion is subirrigated. The remaining area is potentially flood irrigable. <br />Surface waters which could be and were used to irrigate the non - exempted alluvial valley floor <br />would be diverted from the Highline Canal. Water in the Highline Canal is diverted from the <br />Colorado River approximately one mile upstream of the disturbance. The Highline Canal will <br />not be affected by subsidence or by mine discharges. Therefore, the quantity and quality of <br />surface water which supplies the AVF would not be affected by the proposed operations <br />(4.24.3(3)). <br />Discharge from the Roadside and Cameo Mines will have a minor salt loading effect on the <br />Colorado River. The affect on the water quality from this discharge will be to increase the <br />specific conductance and total dissolved solids about 0.2 percent. This, in turn, would have a <br />minor effect on the water which supplies the subirrigated portion of the AVF, since recharge <br />water from the adjacent Colorado River is the source of alluvial groundwater which subirrigates <br />the AVF. <br />During mining, the sediment control system will temporarily reduce surface flows and will <br />remove sediment loads. Sediment ponds will not remove dissolved solids. Thus, the mine <br />operation will increase salt loads. Reduction in flow will only occur during significant <br />precipitation events and possibly during spring snowmelt. During these events, flows will be <br />reduced for only a period of 24 hours. Even then, the amount of water stored in the sediment <br />ponds is minor compared to the average flow of the Colorado River (3549 cfs). <br />All effects from the mining operation will be short- termed. With reclamation and removal of the <br />sediment control system, these effects would be mitigated. Based on the above discussion, the <br />Division finds that the proposed operations will not materially damage the quantity and quality <br />of water in the surface and underground water systems that supply the alluvial valley floor or <br />portions of the alluvial valley floor (4.24.3(3)). <br />3. The mining operations had already disturbed much of the alluvial valley floor within the permit <br />area prior to August 3, 1977, with construction of the overland conveyor and loadout facility. <br />No additional disturbance of this area is planned. The essential hydrologic functions of those <br />areas which will remain undisturbed will be preserved. <br />The permittee identified subirrigation and flood irrigation as the essential hydrologic functions of <br />the AVF. In the past, the Highline Canal, which is immediately upslope of the AVF, has been <br />the source of water for irrigating a portion of the AVF. As described below, no irrigation <br />Permit Revision No. 5 53 July 10, 2012 <br />