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as mining progresses throughout the remainder of the impacted Northern Mining District panels. • Fish Creek Fish Creek flows in a generally northerly direction through the Northern Mining District. The overburden depth varies from 1,000 feet to 1,400 feet through the panels. The location of the creek is shown on Map 23B, Structures and Renewable Resources. The projected impacts to the creek aze presented in Exhibit 7e-6, Twentymile Coal Company, AVF Subsidence Study, Final Report, prepared by Sub Terra, Inc. As noted in the exhibit, subsidence varies from 0 to 67 inches over the panels. Based upon the data presented in Exhibit 7e-6, the maximum increase in the stream gradient is 1.1%. It is not anticipated this will cause significant changes to the creek's profile and resultant erosion should not be a concern. TCC has experienced similaz changes in gradient in the EMD and NMD without resultant erosional problems in either Fish, Foidel or Middle creeks. The same type of subsidence features will occur along Fish Creek, i.e. trough-shaped, ponding will occur over the panels. The ponds mitigate any change in gradient as the velocity of the water diminishes as it passes through the ponded areas. The extent of ponding, i.e. flooding of AVF, is presented in Exhibit 7e-6. As stated in the exhibit approximately 7.3 acres will be flooded by the mining of panels 17 Right and 18 Right.. Prior to full extraction under the creek, a channel survey will be completed to enhance the information used in the preparation of the probable hydrologic consequences section of this application. Fish Creek Alluvial Valley Floor The Fish Creek alluvial valley floor will be undermined and subsided during the mining of panels 17 Right and 18 • Right. The subsidence for the AVF will mirror that projected for the creek. The impacts anticipated for the valley floor would be pooling of water in the subsidence troughs created in panels 17 Right and 18 Right Presently, there are no irrigation headgates located within the panels. This demonstrates that flood irrigation of these bottom lands is not practical and that any enhancement of vegetative growth results from subirrigation. The subsiding of the valley floor will increase the potential for subirrigation to occur. This results from the establishment of the flow point out of the trough at the gateroad. This controls the elevation of the water in the stream in relation to the area of the subsidence trough. As can be visualized, this leads to increasing the area of potential subirrigation. In addition to the ponding that will result from subsiding the AVF, there will be areas within the AVF where the water level will be immediately below the surface, i.e. saturated soil conditions. The impacts of this will be limited due to the fact that the majority of the AVF will be flooded. The overall impact may be a change in vegetation, water tolerant species taking over areas of saturated soils. This will only serve to increase the size of the riparian area, which is not considered a negative impact. I• PR 03-06 2.05-181.10 0/07/03