Laserfiche WebLink
Mr. Kent Gorham <br />April 25, 2011 <br />Page 4 <br />NECC Response: Edge offset is defined as the horizontal distance between the <br />inflection point (the transition point between zones under tension and compression) on <br />the surface and the edge of the mined-out panel. This information is also included in <br />Exhibit 24. <br />10. No indication of panel width was provided in the subsidence analysis in Exhibit 24. <br />Please provide panel width and indicate the vertical projection of the mined area used in <br />the analysis in Figures 1 and 2. <br />NECC Response: Figures 1 and 2 of Exhibit 24 have been modified to indicate the <br />panel width and vertical projection of the mined area. <br />11. No estimate of angle of draw was noted in Exhibit 24. If the complement angle to the <br />angle of influence can be assumed to be the angle of draw, (23.8 degrees) at 450 feet in <br />depth, the projection of measureable subsidence would project outward 198 feet from the <br />vertical projection of the edge of the workings at the surface. If a 300 foot square pillar is <br />used to protect gas wells, and the well is centered in the 300 foot square, 198 feet would <br />intercept the gas well casing in the subsurface from all sides assuming mining and <br />subsidence on all sides of the protective square pillar. In fact, if mining was to occur on <br />all sides, no portion of the surface would be spared from subsidence for the gas wells. <br />This protective pillar area does not appear to be large enough to protect gas wells from <br />possible casing rupture or other damage. Please review Exhibit 24 with regard to <br />subsidence control for the gas wells. <br />NECC Response: Exhibit 24 has been modified to include a detailed discussion of the <br />gas well pillars. <br />12. In permit text narrative, define the term "pillar retreat line" and show in a figure or cross- <br />section how this "line" relates to surface features when used in the context of a <br />subsidence control plan. <br />NECC Response: The pillar retreat line is defined and illustrated in the subsidence <br />control plan Exhibit 24. <br />13. The paved road mitigation plan states "visual monitoring should be performed on the <br />roads weekly beginning when retreat operations are within a 40 degree vertical offset <br />angle." The Division understands that no retreat mining will occur from mining in the <br />Allen Seam in Section 13, 14, 23, and 24 of T33S R68W. This would preclude <br />subsidence of Highway 12, the Purgatoire River, and any structures or residences in the <br />described area. Please explain and/or correct the subsidence control plan as necessary. <br />NECC Response: No retreat mining is planned under Highway 12, the Purgatoire River or <br />residences. Exhibit 24 has been modified to reflect this. <br />14. Subsidence survey, mitigation, and control plan information is found in two locations <br />within the revised materials; on pages 2.05-90g to 2.05-93 and in Exhibit 24 (revised <br />Agapito Associates, Inc.