2022-11-07_REVISION - C1981041 (2)

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All effects from the mining operation will be short-termed. With reclamation and removal of the sediment control system,these effects would be mitigated. Based on the above discussion, the Division finds that the proposed operations will not materially damage the quantity and quality of water in the surface and underground water systems that supply the alluvial valley floor or portions of the alluvial valley floor(4.24.3(3)). The mining operations had already disturbed much of the alluvial valley floor within the permit area prior to August 3, 1977, with construction of the overland conveyor and loadout facility. No additional disturbance of this area is planned. The essential hydrologic functions of those areas which will remain undisturbed will be preserved. 3. The permittee identified subirrigation and flood irrigation as the essential hydrologic functions of the AVF. In the past, the Highline Canal, which is immediately upslope of the AVF, has been the source of water for irrigating a portion of the AVF. As described below,no irrigation presently takes place in the site area. Subirrigation is controlled by the water level in the adjacent Colorado River and is not affected by the reclamation plan. No actions are necessary to reestablish subirrigation. The reclamation procedure will restore the essential hydrologic function of subirrigation. Quantity and quality of water is largely regulated by the Colorado River. Any quality changes resulting from the surface operations will be of short duration due to the close proximity of the Colorado River and the extensive underflow associated with this relatively large surface water flow system. In addition, if a groundwater problem is detected by the monitoring program, mitigation measures will be undertaken prior to reclamation of the site. A flood irrigation system had apparently been abandoned at some point prior to loadout site development in 1977, and areas designated as historically flood irrigated in and adjacent to the permit area, have not been flood irrigated since that time. The quantity of water available from the Highline canal for flood irrigation is 4 A-F per acre and is limited to 14 acres. The original post mining land use for the UTL area was wildlife habitat. The original reclamation plan was to restore the capability of flood irrigation but not necessarily implement flood irrigation. With approval of Permit Revision No. 4, the postmining land use for the loadout area was changed from wildlife habitat to industrial/commercial. This land use change associated with PR-4 will preclude the Operator's from restoring the capability of flood irrigation inside the UTL loop. Exhibit 33 of the permit application package shows the acreage at the UTL area identified as "historically flood irrigated". With PR-4 approval SCC submitted new exhibits for insertion into the permit application package. Exhibit 33-1, Irrigated Fields 10-14-76 and Exhibit 33-2, Potentially Irrigated Fields 11-16-94 show the irrigated fields prior to, and after loadout site development. Based on 63