Laserfiche WebLink
_58_ <br />CWI proposes to control subsidence within these renewable resource lands by <br />limiting the extraction of coal beneath these potentially impacted surficial <br />aquifers. In areas of the renewable resource lands separated from the "D" <br />seam by less than 600 feet, extraction will be limited to seven 20-foot wide <br />mains developed on 120' by 80' centers, resulting in permanently retained 100' <br />by 60' pillars. Pillar stability calculations project Ashwin/Wilson safety <br />factoring in excess of 2.0 for pillars of that size at 600' of overburden <br />depth. Further, in areas of the renewable resource lands separated from the <br />"D" seam by between 600' and 800' of overburden, permanent 60' x 60' pillars, <br />with Ashwin/Wilson safety factoring in excess of 1.5, will be retained. In <br />both of these areas, mining will be limited to development without retreat <br />extraction. <br />With the exception of the ruins depicted as Structure No. 27, the inventoried <br />buildings will be protected by the retention of solid coal pillars of 300' <br />radius beneath each of the potentially affected buildings. <br />CWI 's strain projections anticipate potential, repairable damage (non-material <br />damage) to the two existing water pipelines, the Steven's Gulch Road, assorted <br />trails, ponds, and springs within the permit area. In each case, a preferred <br />repair methodology has been presented within the Subsidence Repair Handbook <br />portion of the permit application N olume 3). <br />Calculations have been included to demonstrate that adequate water storage <br />exists in the Pitkin Mesa Pipeline water distribution system to assure <br />adequate water supplies in the event of asubsidence-related disruption to the <br />pipeline. The company does not propose to mine pillars beneath the Pitkin <br />Mesa Pipeline during the 5-year permit term. Only development mining of main <br />entries would occur under the pipeline and the Stevens Gulch Road within the <br />Stevens Gulch buffer zone and no subsidence is projected. CWI will be <br />required to elaborate upon plans to detect, locate, and repair pipeline <br />ruptures, prior to receiving approval for any pillar extraction or panel <br />development beneath the pipeline, <br />Subsidence Monitoring Program <br />CWI proposes a subsidence monitoring program with three components; visual <br />inspection, wide-spaced grid subsidence monumentation, and closely-spaced <br />high-resolution subsidence monuments. The visual inspection phase consists of <br />a walk-over of the ground surface above mined areas on a semi-annual <br />frequency. In future permit periods, when renewable resource lands and <br />structures may be undermined, pre- and postanining inspections of structures <br />will be incorporated. The applicant also commits to daily inspection of the <br />Steven's Gulch road, in order to protect the public. <br />Monitoring stations No. 1 through No. 27 comprise a wide-spaced monument grid <br />on approximately 1300' centers east-west and 2600' centers north-south. These <br />monuments provide general observations regarding the magnitude of vertical <br />subsidence occurrences. Additional wide-spaced monuments No. 70 through No. <br />87 will be installed above proposed mine workings adjoining the old east <br />portals. Monuments No. 90, 92 & 93 have been installed above the proposed <br />underground workings adjoining the new West Portals. <br />