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(4.24.2(1)). <br />The essential hydrologic functions of the Rapid Creek alluvial valley floor are those geologic, <br />hydrologic, topographic, and soil characteristics that give the area the ability to support flood <br />irrigated agricultural activities. Since no mining activities would take place within the AVF, the <br />geologic, topographic, and soil characteristics of the AVF would be unaffected. Rapid Creek <br />and Cottonwood Creeks would be undermined under a limited extraction plan and mining would <br />not effect the surface water system that supplies the alluvial valley floor. <br />Colorado River Alluvial Valley Floor - Findings <br />The proposed surface coal mining operations would not interrupt, discontinue or preclude <br />farming on an alluvial valley floor that is irrigated or naturally subirrigated. <br />The area designated as alluvial valley floor lies outside of the permit area, downstream from the <br />proposed operations. As a result, there would be no surface disturbance within the AVF, and the <br />area would not be undermined. No irrigation occurs along this stretch of the river where the <br />permit area is located except for undeveloped rangelands which are not significant to farming <br />(4.24.3(1) and 2.06.8(5)(a)(i)). <br />The proposed surface coal mining operations would not materially damage the quantity or <br />quality of water in surface and undergroundwater systems that supply those alluvial valley floors <br />or portions of alluvial valley floors (4.24.3(3) and 2.06.8(5)(a)(ii)). <br />Water for flood irrigated agricultural activities is obtained from two sources. The upper terrace <br />areas at the mouth of Rapid Creek are irrigated by flow from the Rapid Creek system. As <br />discussed above, mining would not affect either water quality or quantity in the Rapid <br />Creek/Cottonwood Creek stream system. <br />Agricultural activities on the lower terraces and floodplain area are flood irrigated with water <br />derived from the Colorado River. Some of the lower areas may be marginally subirrigated by <br />alluvial groundwater. The proposed operation would not affect the quantity of flow in the <br />Colorado River stream/alluvial aquifer system. Disposal of coal refuse material in an adjacent <br />area, and the discharge of mine water from underground workings could affect water quality. <br />The Division has assessed the possible affects of these activities and has not identified any <br />significant change in water quality. <br />Surface coal mining and reclamation operations would be conducted to preserve, throughout the <br />mining and reclamation process, the essential hydrologic functions of the alluvial valley floors <br />(4.24.2(1)). <br />The essential hydrologic functions of the Colorado River alluvial valley floor are those geologic, <br />hydrologic, topographic, and soil characteristics that give the area the ability to support flood <br />irrigated agricultural activities. Subirrigation is a marginal function that is limited to a few of the <br />lower areas which are also capable of flood irrigation. Since no mining activities would take <br />place within the alluvial valley floor, the geologic, topographic, and soil characteristics of the <br />alluvial valley floor would be unaffected. Mining activities are expected to have no effect on the <br />Rapid Creek/Cottonwood Creek hydrologic system. Water quality in the Colorado River <br />Permit Revision No. 4 56 February 3, 2009