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REV00707
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REV00707
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Entry Properties
Last modified
8/25/2016 12:58:22 AM
Creation date
11/21/2007 8:47:40 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1982056
IBM Index Class Name
Revision
Doc Date
5/25/2000
Doc Name
FOIDEL CREEK MINE C-82-056 ADEQUACY LETTER NO 3
From
DMG
To
TWENTYMILE COAL CO
Type & Sequence
PR5
Media Type
D
Archive
No
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r <br />• Pane 2 <br />May ~~, 2000 <br />figure assumes Panel 12 Right will be 1000 fee[ wide, assumes the overburden over Panel 12 Right will be 1400 <br />feet thick. and reflects the influence of Panel l3 Right. <br />From TCC's Map 6, "Wadge Seam Stmcture with Cross Sections", Map 9A, "Geologic Cross Section E-E', and <br />Map 23. "Mine Plan", however. it appears that the thickness of the overburden overlying the eastern end of Panel <br />!'? Ri~}±t is !ess L`tan the thicknesses t:sed in the aene:alion of Fiettres 2 and 3. Borehole 9800, located <br />approximately 3300 feet west of the western edge of Panel 12 Right's start room, indicates an overburden depth <br />of 1020 feet (after adjusting for the cross section's 5:1 vertical exaggeration). Moving east from this borehole <br />toward the eastern end of Panel l2 Right, Borehole 40007 indicates an overburden depth of 830 feet, Borehole <br />40095 indicates an overburden depth of 620 feet, and Borehole 40056 indicates an overburden depth of 480 feet. <br />These thinner overbunden values create higher predicted subsidence values than currently provided in TCC's PR- <br />OS application. As Panel 12 Right will be 1000 feet wide, the ratio of the panel's width to the depth of <br />overburden at Borehole 40007 will be 11(1000 feet/830 feet). Using Figure 1 from TCC's Exhibit 4e-3, <br />"Maximum Subsidence vs Width/Depth for the Foidel Creek Mine", and assuming a coal extraction height of 8.5 <br />feet (TCC's Exhibit 7E, page 6), this ratio of ] .2 results in a predicted subsidence of 76.5 inches (75% of 8.5 feet, <br />converted to inches). This predicted subsidence value is greater than the predicted subsidence values of 62 inches <br />and 56 inches depicted in Figures 2 and 3 of TCC's Exhibit 4e-3. <br />An even greater disparity between predicted subsidence values exists when the National Coal Board formula of <br />S(max) =extraction height x (panel width/overburdenheighr) is used. This formula was used by TCC to predict <br />the maximum amount of subsidence in the Western Mining District (WMD) (Exhibit 7, page 7-5). Using this <br />formula, the maximum predicted subsidence for the area near Borehole 40007 would be 8.5 feet x (1000/830), or <br />101 feet. As this value of predicted subsidence is greater than the 8.5-foot extraction height value, it appears that <br />there could be as much as 8.5 feet (102 inches) of subsidence near Borehole 40007. This value of 102 inches of <br />possible subsidence is much greater than the 56 and 62 inches of subsidence depicted in Figures 2 and 3 of <br />TCC's Exhibit 4e-3. <br />We are aware that TCC predicted that at the eastern end of Panel 12 Right, Foidel Creek would experience from <br />zero to fifty inches of subsidence (TCC Exhibit 4e-3, page 6). While this prediction may indicate in some <br />manner the degree of dampening of subsidence by Panel 12 Right's start room, it is not clear whether TCC's <br />prediction of 0-50 inches of subsidence took into account the thinning overburden at the eastern end of the panel. <br />We therefore request the following from TCC: <br />a) Please indicate where in the PR-OS application the Division may find transverse and start room subsidence <br />profiles for the eastern end of Panel 12 Right that reflect the actual overburden thicknesses of between 480 <br />feet, 620 feet, 830 feet, and 1020 feet depicted on Geologic Cross Section E-E'. <br />b) If these profiles do not exist, we request that TCC develop them and submit them to the Division for review <br />and inclusion into TCC's pennit. <br />c) If TCC develops new subsidence profiles for the eastern end of Panel 1 Z Right, the Division also requests <br />that TCC revise the predicted angle of draw for the eastern end of Panel 12 Right, and develop a map similar <br />to Map 3, "Subsidence Associated with Panel 5 and 6" (TCC's Exhibi[ 7B) that depicts in plan view the extent <br />
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