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9. Please define edge offset. The analysis provided indicates that edge offset <br />was estimated using SDPS guidelines based on panel width and depth of <br />workings. <br />10. No indication of panel width was provided in the subsidence analysis in <br />Exhibit 24. Please provide panel width and indicate the vertical projection of <br />the mined area used in the analysis in Figures 1 and 2. <br />11. No estimate of angle of draw was noted in Exhibit 24. If the complement <br />angle to the angle of influence can be assumed to be the angle of draw, <br />(23.8 degrees) at 450 feet in depth, the projection of measureable <br />subsidence would project outward 198 feet from the vertical projection of the <br />edge of the workings at the surface. If a 300 foot square pillar is used to <br />protect gas wells, and the well is centered in the 300 foot square, 198 feet <br />would intercept the gas well casing in the subsurface from all sides <br />assuming mining and subsidence on all sided of the protective square pillar. <br />In fact, if mining was to occur on all sides, no portion of the surface would be <br />spared from subsidence for the gas wells. This protective pillar area does <br />not appear to be large enough to protect gas wells from possible casing <br />rupture or other damage. Please review Exhibit 24 with regard to <br />subsidence control for the gas wells. <br />12. In permit text narrative, define the term "pillar retreat line" and show in a <br />figure or cross-section how this "line" relates to surface features when used <br />in the context of a subsidence control plan. <br />13. The paved road mitigation plan states visual monitoring should be <br />performed on the roads weekly beginning when retreat operations are within <br />a 40 degree vertical offset angle." The Division understands that no retreat <br />mining will occur from mining in the Allen seam in Section 13, 14, 23, and 24 <br />of T33S R68W. This would preclude subsidence of Highway 12, the <br />Purgatoire River, and any structures or residences in the described area. <br />Please explain and/or correct the subsidence control plan as necessary. <br />14. Subsidence survey, mitigation, and control plan information is found in two <br />locations within the revised materials; on pages 2.05-90g to 2.05-93 and in <br />Exhibit 24 (revised1/12/11). Please consider consolidating this information <br />in one location in the permit application. <br />15. Permit text narrative on page 2.05-90g states that structures are shown on <br />Map 20 sheets 1-3 and Maps 11 and 12. Please indicate where a listing of <br />all the structures and renewable resources is located along with a brief <br />description of each. [Rule 2.05.6(6)(a)(ii)] . <br />16. With regard to mining proposed under TR-56, please state what structures if <br />any, will be undermined and/or affected by subsidence. Permit text narrative