2022-11-07_REVISION - C1981041 (2)

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Alluvial Valley Floor—Findings (Facilities Area) Those portions of the permit area within Sections 26, 27, 28, 33 and 34 are exempt from the requirements that prevent an operation from interrupting, discontinuing, or precluding farming, and from affecting the quantity and quality of water supplying the alluvial valley floor(4.24.3(4)). However,this area is not exempt from the requirements for restoring the essential hydrologic functions of the alluvial valley floor, which will be discussed below, in Item 3. All of the non-exempt alluvial valley floor is located outside the permit area within Section 26 and 27. 1. No portion of the non-exempt alluvial valley floor is presently disturbed by the mining operation. A small portion of this area is indicated as being historically flood irrigated on Exhibit 33. There are no plans to disturb any additional land on the alluvial valley floor. Therefore, the proposed coal mining operation will not interrupt, discontinue, or preclude farming on the alluvial valley floor(4.24.3(l)). 2. As previously discussed, a portion of the non-exempt alluvial valley floor was historically flood irrigated. In addition, a portion is subirrigated. The remaining area is potentially flood irrigable. Surface waters which could be and were used to irrigate the non-exempted alluvial valley floor would be diverted from the Highline Canal. Water in the Highline Canal is diverted from the Colorado River approximately one mile upstream of the disturbance. The Highline Canal will not be affected by subsidence or by mine discharges. Therefore, the quantity and quality of surface water which supplies the AVF would not be affected by the proposed operations (4.24.3(3)). Discharge from the Roadside and Cameo Mines will have a minor salt loading effect on the Colorado River. The effect on the water quality from this discharge will be to increase the specific conductance and total dissolved solids about 0.2 percent. This, in turn,would have a minor effect on the water which supplies the subirrigated portion of the AVF, since recharge water from the adjacent Colorado River is the source of alluvial groundwater which subirrigates the AVF. During mining,the sediment control system will temporarily reduce surface flows and will remove sediment loads. Sediment ponds will not remove dissolved solids. Thus, the mine operation will increase salt loads. Reduction in flow will only occur during significant precipitation events and possibly during spring snowmelt. During these events, flows will be reduced for only a period of 24 hours. Even then, the amount of water stored in the sediment ponds is minor compared to the average flow of the Colorado River(3549 cfs). 62