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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 />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 />presently takes place in the site area. <br />Subirrigation is controlled by the water level in the adjacent Colorado River and is not affected <br />by the reclamation plan. No actions are necessary to reestablish subirrigation. The reclamation <br />procedure will restore the essential hydrologic function of subirrigation. Quantity and quality of <br />water is largely regulated by the Colorado River. Any quality changes resulting from the surface <br />operations will be of short duration due to the close proximity of the Colorado River and the <br />extensive underflow associated with this relatively large surface water flow system. In addition, <br />if a groundwater problem is detected by the monitoring program, mitigation measures will be <br />undertaken prior to reclamation of the site. <br />A flood irrigation system had apparently been abandoned at some point prior to loadout site <br />development in 1977, and areas designated as historically flood irrigated in and adjacent to the <br />permit area, have not been flood irrigated since that time. The quantity of water available from <br />the Highline canal for flood irrigation is 4 A-F per acre and is limited to 14 acres. The original <br />post mining land use for the UTL area was wildlife habitat. The original reclamation plan was to <br />restore the capability of flood irrigation but not necessarily implement flood irrigation. With <br />approval of Permit Revision No. 4, the postmining land use for the loadout area will be changed <br />from wildlife habitat to industrial/commercial. This land use change associated with PR-4 will <br />preclude the Operator's from restoring the capability of flood irrigation inside the UTL loop. <br />Permit Revision No. 4 53 February 3, 2009