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Elk Creek Mine Subsidence Page 4 February 26, 2003 <br />of the east side slope. Therefore, water entering these open ~ <br />fractures will remain in the Bear Creek drainage. • <br />Predicted maximum Elk Creek Mine horizontal compressive I <br />strains (-E) also occur approximately 90 feet inside Panel #1 where <br />Bear Creek crosses over the south and north ribsides. At these I <br />locations the predicted compressive strains are 262O0µ to l5700µ , <br />respectively, see Table 1 and Table Al in Appendix A. Compressive -- <br />strains of the magnitude of 2O000µ will, in the valley fill I <br />alluvium present at the bottom of the Bear Creek drainage, will <br />probably result in compression ridges to a height of approximately <br />2-ft above the ground surface. These compression ridges will run I <br />roughly perpendicular across Bear Creek. Bear Creek will not be <br />blocked by this relatively minor compression ridge because the <br />overall gradient of Bear Creek is toward the south and approaches I <br />15$, 140-ft in the roughly 990-ft long reach of Bear Creek across <br />Panel #1. <br />Predicted trough subsidence and horizontal surface strains I <br />decrease where Bear Creek crosses panels upstream from Panel #1 <br />because of the increasing thickness of the overburden, as indicated <br />on Table 1. The continuing steep gradient of Bear Creek upstream I <br />across Panel #2 in Panel Group 1 and across Panels #12 through #17 <br />in Panel Group 3 and continuing height of the adjacent side slopes <br />of the Bear Creek drainage progressively increases the favorable •' <br />Bear Creek drainage conditions when subjected to longwall panel <br />mining in the Elk Creek Mine. <br />The NCB (1975) reported that surface subsidence over longwall ' <br />panels in virgin ground is normally only 90$ of subsidence measured <br />over longwall panels extracted in previously subsided ground. ' <br />Virgin ground locations around the ribsides of planned southerly <br />Elk Creek Mine longwall panels are indicated in the subsidence <br />calculation tables in Appendix A by a "V" in the "Side-Location" <br />column. Plate 2 for Panel Group 1 and Plate 12 for Panel Group 3 <br />contain a purple lines labeled "Mining Limits in Other Seams" that <br />indicates the parts of Elk Creek Mine that has been previously <br />undermined and is probably subsided ground. All of planned Panels I <br />#1 and #2 of Panel Group 1 and Panels #17, #18 and #19 of Panel <br />Group 3 will be longwall mined over abandoned room and pillar <br />workings in the "C" and "B" Seams and were probably previously ' <br />subsided. Part of planned Panel #3 in Panel Group 1 and Panels #15 <br />and #16 in Panel Group 3 will be longwall mined over abandoned room <br />and pillar workings in the "C" and "B" Seams and those areas were ' <br />probably previously subsided. <br />The interburden thicknesses between the "D" Seam Elk Creek <br />Mine and the underlying "B" and "C" Seam mine workings is ' <br />sufficient to prevent either chimney subsidence or stress I <br />concentrations over barrier pillars in the underlying workings from <br />adversely affecting overlying panels in Panel Group 1 and Panel <br />-4- <br />1 <br />