Laserfiche WebLink
Fall 2009 Subsidence and Geologic Field Observations <br />Box Canyon, Apache Rocks, and South of Divide Mining Areas <br />• 0.00475 (or 0.48 percent). This compares to a range of maximum horizontal strain <br />measurements from 2000 which found 0.75 to 1.5 feet across a crack area totaling 320 feet (or <br />0.23 to 0.47 percent). <br />The maximum horizontal strain value calculated for the most recent field visit is close to the <br />maximum value calculated in 2000. Only the crack area and number of cracks has decreased. <br />Some of the smaller cracks observed to the north in the summer of 2000 have closed, and the <br />southern cracks have become wider over the last several years. <br />The range of maximum horizontal tensile strain values predicted for the Apache Rocks mining <br />area is 0.3 to 1.3 percent (0.003 to 0.013) in Exhibit 60 (Appendix A). The maximum value of <br />horizontal strain measured at Apache Rocks (0.48 percent) is below the median horizontal tensile <br />strain values (0.65 percent) predicted by Dunrud in Exhibit 60. <br />5.20 Photographic Observation Point 6 <br />• This photographic point was not visited during the fall 2009 because mining has yet to occur in <br />the area overlooked by this location. This site is generally visited only once each year during the <br />sprang. <br />5.21 Photographic Observation Point 7 <br />This location was established on September 27, 2007 at the MCC landslide monitoring station <br />that overlooks Monument Dam and Minnesota Reservoir. This photographic observation point <br />(Map 2) was established to provide a baseline for future reference. From this location, various <br />features associated with a relatively large landslide south of the Minnesota Reservoir can be <br />readily identified including the head scarp, hummocky topography, and numerous spring and <br />wetland areas indicating discharge locations for water stored within the landslide mass. Figure <br />57 provides a good fall 2009 overview of Minnesota Reservoir, Monument Dam, and the <br />landslide area to the south (distant side) of the reservoir. <br />831-032.791 Wright Water Engineers, Inc. Page 64 <br />April 2010