2012-05-30_REPORT - C1980007 (8)

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831 - 032.793 May 2012 Fall 2011 Subsidence and Geologic Field Observations Box Canyon, Apache Rocks, and South of Divide Mining Areas 4.1 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 originally included three historic standpipe piezometers (P -1 on the dam crest, P -2 on the dam crest, and PZ -3a south of the spillway and west of the nested piezometers), four boring locations each with three nested piezometers (PZ -06 -01 through PZ- 06 -12), two inclinometer locations (one on the dam INC -4, and one in the landslide area south of the dam which was damaged and is no longer there noted below, INC -5), 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 spring 2010, monitoring and reporting responsibilities for the piezometers and inclinometers on Monument Dam were turned over to the Minnesota Canal and Reservoir Company per their agreement with MCC and the Colorado Division of Water Resources. Nonetheless, Monument Dam piezometer and inclinometer data through fall 2011 is included in this report as Appendix B. Note that INC -5 (Inclinometer 5) was sheared off at 7 feet in May 2009 with no subsequent information collected. This location also included PZ -08 -13 (a vibrating wire piezometer located in the same borehole). Inclinometer 4 (INC -4) is the only other inclinometer associated with the dam at this time. MCC retained monitoring and reporting responsibilities for the land survey stations. Information collected from each of these monitoring locations is also provided in Appendix B. Additional details regarding the Minnesota Reservoir Robotic Total Station (RTS) surveys can be found in the Spring 2011 Report. The Minnesota Reservoir RTS surveys 12 monuments on the dam (6000 series) and 26 monuments on the hillside (Borrow Area) south of Minnesota Creek Road (7000 series). A summary of the survey data is recorded in Table 1 of Appendix B. The table represents a comparison of the Easting, Northing and Elevation displacement from spring 2011 through fall 2011. The differences in Easting, Northing and Elevation displacement (if any) through this time Wright Water Engineers, Inc. Page 26