2010-05-03_REPORT - C1980007 (9)

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Fall 2009 Subsidence and Geologic Field Observations Box Canyon, Apache Rocks, and South of Divide Mining Areas is 2009 for each monument. The differences in height and displacement (if any) through this time period was calculated. Those differences that were within one standard deviation were considered negligible and a difference of zero was input into the table. Monuments with a displacement greater than 0.5 feet were considered to have incurred "significant" movement. In the fall of 2009, considerable complications with software and radio communications, and back-sight and monument damage caused by wildlife and livestock interfered with data collection. In October, the survey instrumentation was removed for maintenance. The instrumentation was returned in December but communication complications persisted resulting in no data recorded for November through December 2009. As reported in the 2009 Spring Subsidence Report, from December 2008 to June 2009, there was no significant movement measured on the dam. From June to October, data showed irregularities inconsistent with hypothetical movement of monuments (i.e. a decrease in height and then a dramatic increase in height is improbable). The June to October time period coincides with the • introduction of livestock in the area. Livestock have been observed moving monuments and misdirecting the back-sights. The changes from December 2008 to October 2009 for the majority of the Monument Dam monuments was a slight increase in height and for the majority of the Borrow Area monuments was a slight decrease in height. Considering that most of the changes in both height and longitudinal displacement for the monuments is minor (f 0-3 inches), it is assumed that the minor measured changes are a product of interference and are considered "insignificant" movement. Those monuments with greater than 3 inches change will be field verified after ground conditions clear and dry this spring. Based on visual observations, little to no change has been observed on Monument Dam and Borrow Area (see Monument Dam Inspection Reports in Appendix Q. Lastly, MCC has an obligation to conduct aerial photographic surveys of the landslides located north and south of Minnesota Reservoir using July 2004 photographs as a baseline reference. Appendix D of this report includes the July 2004 baseline photograph (Map D-1), as well as a photograph of the same area taken in September 2008 (Map D-2) and June 2009 (Map D-3). A comparison of the photographs shows there to be relatively little change except in the area south 831-032.791 Wright Water Engineers, Inc. Page 13 April 2010