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Subsidence cracks occurring across a stream channel could cause the disruption of the stream. However, because <br />of the presence of thick, fine-grained sediments in the stream bed of the study area, the process of sealing the <br />cracks would be fast and no significant impacts on the flow are expected. <br />The occurrence of the subsidence cracks on the surface may not necessarily result in direct inflow into the mine <br />when a surface water body was disrupted. Studies by various authors such as Orchard (1969, 1975) in Great <br />Britain, Williamson (1978) in Australia, and Hydro-Geo Consultants, Inc. in West Virginia (1991) and Ohio <br />(1988), indicated that the subsidence cracks are limited in depth by the development of compressive stresses <br />replacing the tensile stresses that cause surface fracturing. The depth of surface subsidence cracks due to tensile <br />stress does not typically exceed 50 feet. Development of this type of crack would be limited in the unconsolidated <br />sediments of the Foidel and Middle Creek alluviums, which are to 30 feet thick near the confluence of these two <br />streams. The presence of up to 600 feet of marine shales between the ground surface and the mined coal will also <br />limit the impacts of subsidence. <br />TCC has done considerable subsidence monitoring work at the Fish Creek AVF study area, area immediately <br />downstream of RCR N27 culvert in Fish Creek in the WMD, to determine if subsidence would impact the creek and <br />its valley Floor. One component of the work focused on making visual observations of Fish Creek to determine if <br />any cracking was occurring in the creeks' channel. The channel included sections of both sediment and exposed <br />bedrock. The visual observations, which included those made by representatives of the DMG, indicated that no <br />cracking of the channel occurred during longwall mining. <br />Predicted Impacts -Fish Creek It is anticipated that Fish Creek will respond similarly to the response <br />observed in Foidel Creek, which overlies the 7, 8, and 9 Right panels. The response observed is for a pool <br />to form in the subsidence trough for the respective panel. The extent of the pool will be dictated by the <br />r bank height. Typically, the subsidence trough lessens in magnitude as you move from the centerline of <br />the panel until it reaches zero at the angle of draw limit. As was evidenced in the EMD, i.e., no head <br />cutting at gateroads, the formation of the pool decreases erosional potential within the subsided segment <br />of the stream. <br />The pre and post mining gradients of Fish Creek is presented on Table 4 of Exhibit 7e-3. With the formation of the <br />pools over panels ] 3 Right through ] 6 Right, TCC is no[ projecting any erosional problems in the stream channel <br />using the historic Flow data for Fish Creek, and the visual observations along Foidel Creek which overlaid Panels 7 <br />through 9 Right. These observations did not detect any erosional problems caused by TCC's mining operation <br />A potential outcome from creation of the small pools is an increase in water temperature during [he summer <br />months. A look at the historic data for the months of January 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 January 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 period <br />of intent, although both stations reflect temperatures of greater then 19 ° Celsius during July. Station 1002 is <br />located over panel 13 Right and will be the only station impacted by the mining activities. As noted on Table 71, <br />average water temperature range from 16.5° C to 19.2 ° C during June through August and 14.5 ° C during <br />September. The temperatures during January through August are not conducive form maintaining acold-water <br />fishery. Likewise, the water temperatures for Stations 27A 1003 reflect higher temperatures than Station 1002. <br />This would be considered normal given their location on lower Fish Creek. Again, the temperatures are not <br />.conducive for maintaining scold-water fishery. Given the historic warming of the creek during [he summer <br />months, no significant impacts are anticipated to result from the undermining and subsiding of the various <br />segments of Fish Creek. Likewise, [he TDS <br />APPROVES •Il1N 2 ° 2000 <br />PR 99-OS 2.05-164 03/28/00 <br />