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E.rftibit 4e-3, subsidence varies from 0 to 50 inches over this panel. It is not anticipated that this will cause significant <br />changes to the creek's profile and resultant erosion should not be a concern. With the type of subsidence that occurs, <br />i.e. trough-shaped, ponding would be the most likely process to occur; this would merely increase the amount of <br />• riparian habitat along the creek. <br />Prior to full-extraction mining under the creek, a channel survey will be completed to enhance the information used <br />in the preparation of the probable hydrologic consequence section of this application. <br />TCC has subsided a segment of Foidel Creek during the mining of panel 9 Right. As predicted, a small pool of less <br />than 1 acre has developed in this reach of Foidel Creek. During the subsiding of the creek overlying panel 9 Right, <br />flow in the creek was disrupted for approximately 8 hours. The inspection of Foidel Creek showed that the <br />Twentymile Sandstone outcrop intercepted the creek. At one location a crack was noted and is postulated that <br />surface flow in Foidel Creek was disrupted due to surface water entering the fractured sandstone. This disruption <br />of flow was verified by visual observation of flow upstream and downstream of Panel 9 Right. It was noted that <br />flow in Foidel Creek entering the 9 Right Panel was not exiting the subsided area over the panel. Again, this was <br />observed for approximately 8 hours, and based upon the flow monitoring work it took approximately 66 days for <br />the inflow and outflow from the 9 Right Panel to equilibrate. This data is presented on Table 72, Foidel Creek <br />Subsidence Flow Monitoring. <br />A visual observation conducted during March 1997 revealed that the stream bed is sealed and inflow and outflow <br />are approximately equal. The pool remains in place with no visual evidence of sinkholes or deep-seated cracks <br />acting as conduits moving water out of the creek. The semi-annual subsidence report contains the pre- and <br />postmining channel profiles. <br />Additionally, TCC has completed mining of the 8 Right Panel and no disruption of flow was observed in Foidel <br />Creek. The difference in the subsided area over the two panels is the Twentymile Sandstone outcrop occurring in <br />and adjacent to Foidel Creek over the 9 Right Panel. The outcrop is not visible over the 8 Right Panel, rather the <br />• stream bed is comprised of fine grained sediments. This type of environment appears to effectively seal and <br />diminish the potential for the water in the creek to enter the underlying deeper sandstone unit. <br /> <br />APPRG~J~D JUiJ 2 g 2000 <br />PR 99-OS 2.05-181.7 05/25/00 <br />