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Subsidence Evaluation For Exhibit 608 South of Divide Mining Area Page 23 -_. J Jumbo Mountain above mined longwall panels 8 and 9 determined that landslides aze very likely only related to natural mass-gravity movements and not related to mining. Baseline information should be gathered in the eight azeas with low to moderate rockfall potential that are listed in Section 10.2 prior to any mining activities. Evidence of naturally occurring rockfalls-such as remnant boulders at the base of steep slopes, or in the run-out zones of these azeas with a rockfall potential should be documented prior to mining. 11.0 EFFECTS OF SUBSIDENCE AND MINE-INDUCED SEISMIC ACTIVITY ON MAN-MADE STRUCTURES AND RENEWABLE RESOURCES Man-made structures and renewable resources in the South of Divide mining area basically consist of 1) a reservoir (Minnesota Reservoir), 2) stock watering ponds, 3) streams (primarily Dry Fork and the upper part of Lick Creek), 4) roads, and 5) local cabins. Minnesota Reservoir, the ponds, and the Deep Creek Ditch diversion to Dry Fork serve the dual purpose of being both man-made structures and containment structures for the valuable water resources in the azea. Based on annual subsidence observations in the Jumbo Mountain, Apache Rocks, and Box Canyon mining azeas during the last nine years, the following information is considered • appropriate for the South of Divide mining azea. 11,1 Minnesota Reservoir Minnesota Reservoir, which provides storage water primarily for irrigation, is located between two landslides--one beginning at the north shore and the other beginning at the south shore. As explained in Section 10.1.1 (above), landslide movement on Jumbo Mountain occurred during unusually wet periods before mining began, during mining, and after mining and subsidence was complete. The conclusions were that landslide movement occurs in response to ground saturation and is not noticeably affected by subsidence and seismic activity produced by longwall mining beneath, or neaz, landslide azeas. Both the landslides on Jumbo Mountain and those north and south of Minnesota Reservoir occur in surficial material (loose rock, gravel, sand, silt, clay, and soil) and local bedrock outcrops. The author therefore expects that the mining of longwall panel E9 will not noticeably affect the large landslide south of Minnesota Reservoir. Mining of the nine longwall mining panels in the South of Divide mining azea, as currently planned (Map 1) will not affect Minnesota Reservoir. The reservoir is located outside the azea of mining influence, using the most conservative 45-degree angle of draw. In order to verify and demonstrate the accuracy of predicfions, based on the results of past subsidence observations in the Apache Rocks and Box Canyon mining azeas, it is recommended that three procedures be implemented to monitor this structure prior to mining. The following procedures will be implemented in order to account for seasonal precipitation changes. 831-032.620 Wright Water Engineers, Inc