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Fall 2017 Subsidence and Geologic Field Observations <br />South of Divide and Dry Fork Mining Areas <br />2.0 GENERAL SUBSIDENCE OBSERVATION AND REPORTING <br />Based on field observations from 1996 to fall 2017, the effects of longwall mining above the West <br />Elk Mine have been less than initially projected as reported in Exhibit 60 (Dunrud, 1998 rev.) and <br />60E (Wright Water Engineers, Inc. [WWE], 2012). Rockfalls and/or landslides have generally <br />been observed only sporadically in the Box Canyon mining area since 2006 where the steep, upper <br />reaches of Sylvester Gulch and Box Canyon abut the large geographic feature known as West <br />Flatiron. In the flatter and more rounded topography of the Apache Rocks, SOD, and Dry Fork <br />mining areas, the rockfall and landslide potential is much smaller. However, subsidence -related <br />tension cracks have occurred in these mining areas, particularly above the active longwall mining <br />face. <br />E -seam longwall mining in the SOD mining area was initiated on Panel E1 in December 2008 <br />beginning at the east end and progressing westward. All mining in the SOD mining area is planned <br />to progress from the east end of the panels toward the west. As of the time of our fall 2017 field <br />visit (October 6), mining was complete in E -seam Longwall Panels E1, E2, E3, E4, E5, and E6. <br />Mining of Longwall Panel E7 was initiated in early August 2017 and was approximately 20% <br />complete as of the time of our fall 2017 field visit. <br />Beginning with the Spring 2011 Subsidence Report, an effort was made to reduce the size of the <br />semi-annual subsidence reports by eliminating much of the regularly included background and <br />historical information (e.g., subsidence projections). For this reason, specific details associated <br />with subsidence projections and field recognition of subsidence and non -subsidence features were <br />eliminated. Since that time, readers have been directed to Sections 1.0 and 2.0, respectively, of <br />the Spring 2011 Subsidence Report and to Exhibits 60 and 60E of the West Elk Mine permit for <br />this information. <br />Also, in keeping with the goal of a reduction in report size, future reports will focus on the <br />identification and discussion of those observations that reflect an obvious change in the conditions <br />overlying the active portion of the mine and on documenting baseline conditions in areas that have <br />yet to be mined. For this reason, observations from our fall 2017 field visit were focused on areas <br />above E -seam Longwall Panels E5, E6, and E7 in the SOD and Dry Fork mining areas. <br />831-032.799 Wright Water Engineers, Inc. Page 5 <br />February 2018 <br />