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West Elk Mine <br />Subsidence Survey. Subsidence Monitorine and Subsidence Control Plan - 2.05.6 (6) (a-fl <br />The extraction of the B Seam coal in the Box Canyon pemut azea, the B and E Seams in the <br />Apache Rocks permit area, and the E Seam mining in the South of Divide permit revision area <br />will be completed using longwall mining methods. The resulting disequilibrium due to longwal] <br />mining may result in surface subsidence, dependent on a number of inter-related factors. As stated <br />by Peng in Surface Subsidence Engineering (1992), "When total extraction is used, it produces a <br />lazge void in the coal seam and disturbs the equilibrium conditions of the surrounding rock strata. <br />The rock strata bend downward while the floor heaves. When the excavated azea (gob) expands to a <br />sufficient size, the roof strata will cave. As a result, the overlying strata continue to bend and break <br />until the piles of the fallen rock fragments are sufficiently high to support the overhanging strata. At <br />this time, the overlying strata no longer cave, but bend and rest on the underlying strata. Strata <br />bending hi subsidence develop upwazd until reaching the surface and forming a subsidence basin. <br />The whole overburden strata and the surface subsidence basin will further go through a period of <br />compaction and gradually become stabilized." <br />The purpose of this section is to describe on asite-specific basis, and to quantify to the extent <br />feasible, the various phenomena that are embodied in this definition. This section provides an <br />inventory of structures and renewable resource lands in the current permit azea, which includes the <br />South of Divide permit revision area, as well as a subsidence survey analysis, potential subsidence <br />consequences, and the subsidence monitoring and control plan. Table 42 of this section provides a <br />list of symbols and definitions for commonly used terms associated with subsidence and used <br />frequently in this section. <br />• It is essential to present the meanings of the following terminology relative to <br />understanding this portion of the permit revision text. To further facilitate an <br />understanding of the areas associated with each geographic expression, see Map lA (and <br />Figure 1 of Exhibit 60B and Figure 2 of Exhibit 60C). <br />Apache Rocks Mining Area -The Apache Rocks mining area encompasses all of the longwall <br />mining panels in Sections 26, 27, 28, 29, and 30, T13S, R90W, 6th P.M. See also Map 52. <br />Apache Rocks Minine Area, East and West Panels -The Apache Rocks west panels refer to <br />the three western panels in the Apache Rocks mining area which are located in Sections 28, <br />29, and 30, T13S, R90W, 6th P.M. Both B and E Seam longwall mining are planned in this <br />area. The Apache Rocks east panels refer to the four eastern panels in the Apache Rocks <br />mining area (longwall panels 145E through 17SE), which are located in Sections 26 and 27, <br />and a portion of Section 35 T13S, R90W, 6th P.M. Only B Seam mining is planned in this <br />area. <br />Box CanYOn Minim Area -This area is designated on Map lA and includes longwall panels <br />18NE through 23NE located in portions of Sections 10, 11, 13, 14, 15, 22, 23, and 24 T13S, <br />R90W, 6t° P.M. The Box Canyon permit revision area encompasses the remainder of the Box <br />Canyon lease tract. Only B Seam mining is planned in this area. <br />West Flatiron Minine Area -- This area is designated on Map lA and includes extensions of <br />longwall panels 18A,18, and 19. <br />1.05-93 Revised June 2005 PRIG <br />