Laserfiche WebLink
2004 Geologic Hazard Field Observations <br />South of Divide Mining Area <br /> <br />• <br />• <br />Mining of the nine longwall mining panels in the South of Divide mining area, as currently <br />planned (Map 1) will not affect Minnesota Reservoir. The reservoir is located outside the azea of <br />mining influence, using the most conservative 45-degree angle of draw. <br />9.2 Stock Watering Ponds and US Forest Service Water Resources <br />The stock watering ponds in the South of Divide mining azea are located primarily in debris <br />flows or colluvium derived from the debris flows. A total of 26 ponds have been mapped in the <br />South of Divide mining azea. Ten of these ponds aze also classified as U.S. Forest Service Water <br />Resources (Map 1). The debris flows consist of a heterogeneous fo locally stratified mixture of <br />clay derived from the Wasatch Formation and boulders, gravel, and sand derived primarily from <br />the Mount Gunnison intrusive (granodiorites and quartz monzanites). Based on observations <br />made during geologic mapping in the area, these debris flows are even less likely to be affected <br />by longwall mining than the alluvium The debris flows have a very low permeability and, <br />because the clay matrix is armored by the interstitial gravel and boulders, are resistant to erosion <br />(the Deep Creek Ditch locally flows in this material at steep gradients). Based on the above- <br />mentioned observations, the clay-rich material that lines these ponds is expected to provide a seal <br />against subsidence effects when the ponds in the South of Divide mining azea aze undermined <br />No stock watering ponds in the Apache Rocks and Box Canyon mining azeas have been <br />noticeably affected when longwall mining occurred beneath them. For example, the ponds above <br />mined longwall panels 13-A, 15, 16, and 22 in Horse Gulch, Sylvester Gulch (stock ponds P27-2 <br />and P27-3), and West Flatiron (stock pond P23-4) respectively, showed no noticeable water level <br />change when compared to pre-mining water levels (after taking seasonal precipitation levels into <br />account). These ponds, which are located in clay-rich (Wasatch clay) material in order to <br />minimize leakage, occur in overburden that ranges in depth from about 800 feet above the <br />southern limit (within the azeas of influence) of mined longwall panel 13-A in Horse Gulch to <br />2,200 feet in the stock pond P23-4 above the eastern end of mined longwall pane122. <br />831-032.621 <br />November 2004 <br />Wright Water Engineers, Inc. <br />Page 33 <br />