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-21- <br />• • <br />Alluvial Valley Floor - Findings (cont'd) <br />Based on the above discussion, the Division finds that the proposed.,Qperations <br />will not materially damage the quantity and quality of water in the surface and <br />underground water systems that supply the alluvial valley floor or portions of the <br />alluvial valley floor. <br />3. The mining operations have already disturbed much of the a1l.uvial valley floor <br />under permit No. 77-442, with construction of the overland conveyor and loadout <br />facility. No additional disturbance of this area is planned. The essential <br />hydrologic functions of those areas which will remain undisturbed will be preserved. <br />The applicant will be required to restore the essential hydrologic functions on the <br />entire alluvial valley floor where disturbance has occurred. There are no "grand- <br />fathering"provisions for restoring the essential hydrologic functions on an alluvial <br />valley floor. <br />The applicant identified subirrigation and flood irrigation as the essential hydrologic <br />functions of the AVF. In the past, the Highline Canal, which is immediately upslope <br />of the AVF, has been the source of water for irrigating a portion of the AVF. No <br />irrigation presently takes place in the site area. subirrigation is controlled by <br />the water level in the adjacent Colorado River. <br />Reclamation and restoration of the essential hydrologic functions will involve <br />removing all facilities, regrading to the approximate original river terrace <br />topography, replacing topsoil and revegetating. A flood irrigation system will be <br />reestablished and the system will be connected to the Righline Canal. This will <br />provide for restoration of the essential hydrologic function of flood irrigation. <br />The reclamation procedure should also restore the essential hydrologic function of <br />subirrigation. Quantity and quality of water is largely regulated by the Colorado <br />River. Any quality changes resulting from the surface operations will be of short <br />duration due to the close proximity of the Colorado River and the extensive underfloor <br />associated with this relatively large surface water flow system. In addition, if a <br />ground water problem is detected by the monitoring program, mitigation measures will <br />be undertaken prior to reclamation of the site. <br />Powderhorn Coal Company will monitor shallow ground water levels at 3 piezometers and <br />at one well near the unit train loadout facility. Water levels will be taken monthlg, <br />and water quality samples will be collected on a quarterly basis from the well. The <br />well is located near the coal storage pile to monitor the effects of leaching of <br />the coal storage pile. <br />Rapid/Cottonwood Creek Area <br />Four distinct areas were examined for identification of alluvial valley floors in <br />the vicinity of Rapid Creek and Cottonwood Creek. These areas were Cottonwood <br />Creek, Rapid Creek, minor ephemeral streams and the Colorado River adjacent to .the <br />Rapid Creek and Cottonwood Creeks watersheds. None of these areas are covered by <br />the "grandfathering" exemption. <br />The Cottonwood Creek valley does not meet the geomorphic characteristics of an <br />alluvial valley floor. The valley is narrow, and any fill material does not meet <br />the AVF size criteria. <br />Valley fill deposits located along Rapid Creek have been interpreted as a mudfZow <br />fan deposit which has been modified and reoworked by Rapid Creek to form three <br />terrace levels. The upper terraces (T2 and T3) are irrigated or have been irrigated <br />Y Y.I I~ <br />