2013-09-27_REPORT - C1980007 (4)

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Spring 2013 Subsidence and Geologic Field Observations South of Divide and Dry Fork Mining Areas (E -Seam) relative to E -seam mining. A memorandum outlining this analysis and conclusion can be found in Appendix B of this report along with Map B -1 showing the 120 survey monuments associated with the subsidence monitoring grid. 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 2.1 with the dam inspection forms and collected data provided in Table 1 of Appendix C. In addition, regular inspections of U.S. Forest Service (USFS) roads and stock ponds are completed by MCC personnel (Appendix D). Ongoing subsidence survey data from the Dry Fork of Minnesota Creek (Dry Fork) channel is shown in Table 1 of Appendix E. In an effort to continue to reduce the size of the report, Appendix E has been condensed to show only the points that have shown subsidence or have been mined under within the last year. All other points have shown no substantial subsidence in eight consecutive quarters and have been removed from the Table. Furthermore, the Lower Cow Camp has shown three consecutive quarters of no substantial subsidence and has similarly been removed from the report. See previous reports for earlier subsidence data. Data and discussions associated with Section 2.1 and Appendices C -E are the responsibility of MCC and provided in this WWE report for convenience. 2.1 Monument Dam /Minnesota Reservoir Monitoring Data Beginning in 2006, numerous monitoring stations were established on Monument Dam and at strategic locations around Minnesota Reservoir as a means to collect baseline information about water levels and potential surface /subsurface movement. Monitoring locations include 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 network during 2007 and 2008. Beginning in the spring 2010, the Minnesota Canal and Reservoir Company took over the monitoring and reporting responsibilities for the piezometers and inclinometers on Monument Dam per their agreement with MCC and the State Engineer's Office. MCC retained monitoring and reporting responsibilities for the land survey stations. Data 831 - 032.795 Wright Water Engineers, Inc. Page 4 September 2013