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features within the rock sequence , such as joints and faults . <br /> r � <br /> Topographic -features such as extensive (compared to mine <br /> depth) abrupt slope changes also affect angle of draw . <br /> The angle of draw has been measured in rocks <br /> similar to those in Coal 13asin as 120 to 200 . It is <br /> believed that an average of 150 would include the worst <br /> case situation , therefore , the horizontal distance from <br /> the rib lines of the mine pan,.l to the edge of disturbance <br /> would be : <br /> x ' = h tan 15° cos ` 9 <br /> x ' = horizontal projection of the limit of draw <br /> corrected for topographic slope <br /> h = vertical depth from coal to the surface <br /> A = the angle of slope taken from the horizontal <br /> Depth from the surface to the B Bed ranges <br /> from 2200 feet to 2800 feet throughout most of the planned <br /> mining area during the five year permit period . Therefore , <br /> subsidence could occur on the surface from 600 to 750 feet <br /> from the vertical extension of the edge of the coal to be <br /> mined . <br /> In summary , this analysis of worst case <br /> surface subsidence concludes that the maximum vertical <br /> disturbance above the Coal Basin underground workings <br /> would be 13 . 2 feet . The analysis also concludes that a <br /> 150 worst case angle of draw could result in horizontal <br /> subsidence occurring on the surface from 600 to 750 feet <br /> U from the vertical extension of the edge of the mined coal . <br /> (See Appendix IV—F-3 for further discussion on the angle of draw) . <br /> 28 <br />