2009-11-13_REPORT - C1980007 - Laserfiche WebLink

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Spring 2009 Subsidence and Geologic Field Observations Box Canyon, Apache Rocks, and South of Divide Mining Areas • subsidence monitoring report with specific survey data summarized in Appendix B and shown on Map B -1. MCC has been collecting data from numerous monitoring locations in and around Minnesota Reservoir and Monument Dam for the last several years. A general discussion of the data collected to date is provided in Section 3.2 with the specific data provided in Appendix C. Lastly, Section 3.3 of this report presents pre- and post- mining survey data from several locations over B -seam Longwall Panel 25. Data specific to these surveys are presented in Appendix D. 3.1 E1 Panel Subsidence Monitoring Grid The West Elk Mine has historically extracted coal mainly from the B -seam of the Mesaverde Formation. Beginning in 2009, extraction of coal from the E -seam (i.e., a unit approximately 300 feet above the B -seam) is occurring in the SOD mining area. As part of the ongoing data collection and monitoring programs required under its permit, an E -seam subsidence monitoring • grid was proposed, developed and constructed. This grid is located above E -seam Longwall Panel 1 (El) and is comprised of 120 points in one longitudinal and two transverse monument lines relative to the panel orientation (see Map 2 and also Map B -1 of Appendix B). The two transverse traverses extend beyond the gate road of Longwall Panel E1 both to the north and south. The southern end of these traverses extends to approximately the middle of Longwall Panel E2 (at least 700 feet outside the edge of the panel). Appendix B of this report includes a tabular summary of the May 2009 survey descriptor, northing coordinate, easting coordinate, and elevation at each of the 120 observation points and compares this information to pre- mining surveys of the same locations conducted in the fall of 2008 and the fall of 2007. This tabular comparison includes a column which represents the relative elevation difference between the May 2009 and October 2008 surveys. Please note that 2008 construction activities along the access roads over the E1 panel resulted in the destruction of twelve survey monuments. All but two of these monuments have been subsequently reset and resurveyed as represented in Appendix B. As expected, the baseline elevations for these reset • monuments have changed. Both of the baseline surveys (i.e., 2007 and 2008) were conducted 831 - 032.791 Wright Water Engineers, Inc. Page 11 November 2009