Laserfiche WebLink
flow, sediment load, and sediment characteristics will all influence the advent or extent of damage that may <br /> require repair. <br /> 4 ,-- Predicted Impacts - Fish Creek It is anticipated that Fish Creek will respond similarly to the response observed <br /> in Foidel Creek, which overlies the 7 -, 8 -, and 9 -Right Panels. The response observed is for a pool to form in <br /> the subsidence trough for the respective panel. The extent of the pool will be dictated by the bank height. <br /> Typically, the subsidence trough lessens in magnitude as you move from the centerline of the panel until it <br /> reaches zero at the angle of draw limit. As was evidenced in the EMD, i.e., no head - cutting at gateroads, the <br /> formation of the pool decreases erosional potential within the subsided segment of the stream. <br /> The pre and postmining gradients of Fish Creek are presented on Table 4 of Exhibit 7e -3. With the formation of <br /> the pools over Panels 13 -Right through 16- Right, TCC is not projecting any erosional problems in the stream <br /> channel, using the historic flow data for Fish Creek, and the visual observations along Foidel Creek which <br /> overlaid Panels 7- through 9- Right. These observations did not detect any erosional problems caused by TCC's <br /> mining operations. <br /> The pre and postmining gradients of Fish Creek are presented on Table 4 of Exhibit 7e -6, Twentymile Coal <br /> Company, AVF Subsidence Study, Final Report. With the formation of the pools over Panels 17 -Right and 18- <br /> Right, TCC is not projecting any erosional problems in the stream channel, using the historic flow data for Fish <br /> Creek, and the visual observations along Fish Creek which overlaid Panels 13- through 14- Right. These <br /> observations did not detect any erosional problems caused by TCC's mining operations. <br /> A potential outcome from creation of the small pools is an increase in water temperature during the summer <br /> months. A look at the historic data for the months of June through September indicates that the segment of Fish <br /> Creek to be subsided during this five -year term already exhibits elevated temperatures during this period. The <br /> historic data is presented in Table 71, Period of Record Average Temperatures, dated June through September. <br /> • Stations 16 and 302 are upstream of the subsided area and will not be impacted by the proposed mining in the <br /> Northern Mining District. As reflected in the data, these stations record the coolest temperatures during the <br /> period of intent, although both stations reflect temperatures of greater then 18° Celsius during July. Station <br /> 1002 is located over Panel 13 -Right and will be the only station impacted by the mining activities. As noted on <br /> Table 71, average water temperature range from 16.3 to 19.1° C during June through August, and 14.2° C <br /> during September. The temperatures during June through August are not conducive form maintaining a cold- <br /> water fishery. Likewise, the water temperatures for Stations 27A and 1003 reflect higher temperatures than <br /> Station 1002. This would be considered normal given their location on lower Fish Creek <br /> Again, the temperatures are not conducive for maintaining a cold -water fishery. Given historic flow declines in <br /> the creek during the summer months, no significant impacts are anticipated to result from the undermining and <br /> subsiding of the various segments of Fish Creek. Likewise, the TDS concentrations are low enough at this point <br /> to believe that there will be no impacts to TDS concentrations in these pools. TCC is planning to recirculate <br /> underground water so that discharge to Fish Creek is not increased over the historic level during the NMD <br /> permit year. Therefore, there should be no quality impact to the streams due to the continued mining in the <br /> Northern Mining Districts. The exception to this is the short-term impact associated with dewatering the <br /> reservoir in the WMD. This is discussed in TR 99 -32. <br /> Mining of the WMD will result in undermining and subsidence of areas underlying the Fish Creek channel over <br /> Panels 12 -, 13 -, and 14 -Left. Given that TCC has previously undermined and subsided Panels 12- through 19- <br /> Right in the NMD with no adverse effect on the Fish Creek channel, it is reasonable to anticipate that the <br /> proposed mining in the WMD will have similar effects on the overlying segment of the Fish Creek channel. <br /> Actual Impacts — Fish Creek TCC has subsided segments of Fish Creek over longwall Panels 12- through 19- <br /> Right. As documented by the Semi - Annual Subsidence Reports for the period 2001 through 2008, subsidence <br /> did not result in any measurable loss of flow or significant ponding in Fish Creek. Minor ponding was <br /> observed, particularly where the existing Fish Creek culverts pass under the Union Pacific Railroad Spur, <br /> however, this minor ponding did not result in any significant observed erosion or water quality impacts. <br /> PRO9 -08 2.05 -163 04/29/09 <br />