2016-04-19_REPORT - C1980007 (6)

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Fall 2015 Subsidence and Geologic Field Observations South of Divide and Dry Fork Mininq Areas 4.0 OTHER SUBSIDENCE -RELATED DATA In addition to the semi-annual traverses conducted by WWE above longwall mining areas, MCC has been collecting data from numerous other monitoring locations. For example, regular inspections of USFS roads and stock ponds are performed by MCC personnel. Copies of these inspection forms can be found in Appendix A. MCC also collected substantial information from the vicinity of Minnesota Reservoir and Monument Dam, such as visual inspections, survey data, and annual aerial photo comparisons (Appendices B and C). In addition, MCC monitors USFS water resources in the vicinity of mining (Appendix D). Also included is a map (Appendix E) of the actual extent (as of the date of the map) of the mined E -seam longwall panels within the Maximum Projected Areal Extent of Potential Mineable E -seam as shown on approved Permit Map 51. Within these appendices, note that the term "recent displacement" indicates that the displacement shown is the difference in the measurements recorded in the last two surveys. A general discussion of the Minnesota Reservoir and Monument Dam follows in Section 4.1 with the data provided in Appendix B. An annual aerial photographic comparison of the Minnesota Reservoir/Monument Dam area is conducted each fall to assess movement in the landslides north and south of the reservoir. This discussion and these aerial images are found in Section 4.2 and Appendix C. Section 4.3 discusses the 2015 Water Resources Project Survey Report for the USFS as required in the permit and included as Appendix D. Data and discussions associated with Sections 4.1 and 4.3 are the responsibility of MCC and are provided in this WWE report for convenience. 4.1 Monument Dam/Minnesota Reservoir Monitoring Data Beginning in 2006, numerous monitoring stations were established on Monument Dain and at strategic locations around Minnesota Reservoir as a means to collect baseline information about water levels and potential surface/subsurface movement. Monitoring locations included three historic standpipe piezometers, four boring locations each with three nested piezometers, two inclinometer locations (one on the dam and one in the landslide area south of the dam), and numerous survey mirrors for evaluation of surface movement on and near the dam. Many of these locations have been monitored monthly from July 2006, while others were added to the monitoring 831-032.797 Wright Water Engineers, Inc. Page 23 March 2016