Laserfiche WebLink
The operator has completed strain projections for the structures inventoried on Map 9 -7. Strain <br />projections have also been completed for the Pitkin Mesa and the Bowie No. 1 Mine water <br />supply water pipelines which cross the potential subsidence zone of the life -of -mine area. The <br />Pitkin Mesa pipeline supplies potable water to roughly 160 domestic taps. <br />Subsidence Control Plan <br />The operator has proposed a subsidence control plan to prevent material damage from occurring <br />to the renewable resource lands within Steven's Gulch and East and West Roatcap Creeks. The <br />U.S. Bureau of Land Management Lease C -37210 also bears stipulations addressing these same <br />concerns. <br />The operator proposed to control subsidence within these renewable resource lands by limiting <br />the extraction of coal beneath these potentially impacted surficial aquifers. In areas of the <br />renewable resource lands separated from the D seam by less than 600 feet, extraction was to be <br />limited to seven 20 -foot wide mains developed on 120 -by -80 -foot centers, resulting in <br />permanently retained 100 -by -60 -foot pillars. Pillar stability calculations project Ashwin/Wilson <br />safety factoring in excess of 2.0 for pillars of that size at 600 feet of overburden depth. Further, <br />in areas of the renewable resource lands separated from the D seam by between 600 and 800 feet <br />of overburden, permanent 60 -by -60 -foot pillars, with Ashwin/Wilson safety factoring in excess <br />of 1.5, were to be retained. In both of these areas, mining was limited to development without <br />retreat extraction. Technical Revision No. 17 (TR -17) and Technical Revision No. 19 (TR -19) <br />address mine plan modifications to Panel B and Panel C respectively. These TR's modify the <br />pillar size and spacing scheme described above, while maintaining the required safety factors. <br />Both revisions were approved by the Division. <br />With the exception of the ruins depicted as Structure No. 27, the inventoried buildings have been <br />protected by the retention of solid coal pillars of 300 -foot radius beneath each of the potentially <br />affected buildings. <br />The operator's strain projections anticipate potential, repairable damage (non - material damage) <br />to the two existing water pipelines, the Steven's Gulch Road, assorted trails, ponds, and springs <br />within the permit area. In each case, a preferred repair methodology has been presented within <br />the Subsidence Repair Handbook portion of the permit application (Volume 3). <br />Calculations were included in the permit application to demonstrate that adequate water storage <br />exists in the Pitkin Mesa Pipeline water distribution system to assure adequate water supplies in <br />the event of a subsidence related disruption to the pipeline. The company did not propose to <br />mine pillars beneath the Pitkin Mesa Pipeline. Only development mining of main entries were to <br />occur under the pipeline and the Steven's Gulch Road within the Steven's Gulch buffer zone and <br />no subsidence was projected. BRL submitted a pipeline repair plan, signed by Pitkin Mesa <br />Pipeline Company as a condition of the approval of TR -19. <br />Technical Revision No. 22 modified the coal lease and permit boundary to the west. The revised <br />permit boundary included areas in the Long Draw Drainage. Upper Cabin Spring, water supply <br />for Stucker Mesa Domestic Water Company, is located in the upper reaches of this draw. BRL <br />submitted to the Division a signed copy of a water replacement plan agreement between BRL <br />and Stucker Mesa Domestic Water Company (see permit application, Volume IA, Section <br />2.05.6). <br />Page 35 of 42 <br />