2013-10-17_PERMIT FILE - C1982056A (4)

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flow, sediment load, and sediment characteristics will all influence the advent or extent of damage that may require repair. Predicted Impacts - Fish Creek It is anticipated that Fish Creek will respond similarly to the response observed in Foidel Creek, which overlies the 7 -, 8 -, and 9 -Right Panels. The response observed is for a pool to form in the subsidence trough for the respective panel. The extent of the pool will be dictated by the bank height. Typically, the subsidence trough lessens in magnitude as you move from the centerline of the panel until it reaches zero at the angle of draw limit. As was evidenced in the EMD, i.e., no head - cutting at gateroads, the formation of the pool decreases erosional potential within the subsided segment of the stream. The pre and postmining gradients of Fish Creek are presented on Table 4 of Exhibit 7e -3. With the formation of the pools over Panels 13 -Right through 16- Right, TC is not projecting any erosional problems in the stream channel, using the historic flow data for Fish Creek, and the visual observations along Foidel Creek which overlaid Panels 7- through 9- Right. These observations did not detect any erosional problems caused by TC's mining operations. The pre and postmining gradients of Fish Creek are presented on Table 4 of Exhibit 7e -6, Twentymile Coal Company, AVF Subsidence Study, Final Report. With the formation of the pools over Panels 17 -Right and 18- Right, TC is not projecting any erosional problems in the stream channel, using the historic flow data for Fish Creek, and the visual observations along Fish Creek which overlaid Panels 13- through 14- Right. These observations did not detect any erosional problems caused by TC's mining operations. A potential outcome from creation of the small pools is an increase in water temperature during the summer months. A look at the historic data for the months of June through September indicates that the segment of Fish Creek to be subsided during this five -year term already exhibits elevated temperatures during this period. The historic data is presented in Table 71 , Period of Record Average Temperatures, dated June through September. Stations 16 and 302 are upstream of the subsided area and will not be impacted by the proposed mining in the Northern Mining District. As reflected in the data, these stations record the coolest temperatures during the period of intent, although both stations reflect temperatures of greater then 18° Celsius during July. Station 1002 is located over Panel 13 -Right and will be the only station impacted by the mining activities. As noted on Table 71, average water temperature range from 16.3 to 19.1° C during June through August, and 14.2° C during September. The temperatures during June through August are not conducive for maintaining a Cold- water fishery. Likewise, the water temperatures for Stations 27A and 1003 reflect higher temperatures than Station 1002. This would be considered normal given their location on lower Fish Creek Again, the temperatures are not conducive for maintaining a cold -water fishery. Given historic flow declines in the creek during the summer months, no significant impacts are anticipated to result from the undermining and subsiding of the various segments of Fish Creek. Likewise, the TDS concentrations are low enough at this point to believe that there will be no impacts to TDS concentrations in these pools. TC is planning to recirculate underground water so that discharge to Fish Creek is not increased over the historic level during the NMD permit year. Therefore, there should be no quality impact to the streams due to the continued mining in the Northern Mining Districts. The exception to this is the short-term impact associated with dewatering the reservoir in the WMD. This is discussed in TR 99 -32. Mining of the WMD will result in undermining and subsidence of areas underlying the Fish Creek channel over portions of Panels 12 -, 13 -, 14 -, and 15 -Left. Given that TC has previously undermined and subsided Panels 12- through 19 -Right in the NMD with no adverse effect on the Fish Creek channel, it is reasonable to anticipate that the proposed mining in the WMD will have similar effects on the overlying segment of the Fish Creek channel. Actual Impacts — Fish Creek TC has subsided segments of Fish Creek over longwall Panels 12- through 19- Right. As documented by the Semi- Annual Subsidence Reports for the period 2001 through 2008, subsidence did not result in any measurable loss of flow or significant ponding in Fish Creek. Minor ponding was observed, particularly where the existing Fish Creek culverts pass under the Union Pacific Railroad Spur, however, this minor ponding did not result in any significant observed erosion or water quality impacts. TR 13 -82 2.05 -163 02/28/13