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Subsidence and Geologic Field Observations <br />Apache Rocks and Box Canyon Mining Areas <br />July 12-15, 2004 <br />1.0 SUMMARY OF MAJOR FINDINGS <br />After six years of observations (three yeazs pre-mining and three years post-mining), no <br />subsidence features have been observed in alluvium above longwall panels that were mined in <br />the Apache Rocks or Box Canyon mining aeeas. In particulaz, no subsidence features (cracks or <br />bulges) were observed in Deep Creek within the area of mining influence of mined longwall <br />panels 14 through 17 (overburden depth to the BSeam-about 1,050 to 1,100 feet), nor were any <br />subsidence features observed in Sylvester Gulch above mined longwall panels 14, 15, and 16 <br />(overburden depth to the BSeam-about 900 to 1,600 feet). <br />The two stock watering ponds located above the headgate entries of mined longwall panel 15 <br />(Twin Ponds), as well as the pond located at the eastern edge of mining longwall pane122 (Pond <br />P23-4), showed no noticeable water level difference compared to annual observations in yeazs <br />prior to the mining of longwall panels 15 and 16. The yieldable and relatively impermeable clays <br />and silts present in the alluvium and much of the colluvium in this portion of these stream <br />valleys, which is derived from the Wasatch Formation, helps provide slow-permeable seal for <br />the stock ponds and arupture-free yieldable material in subsidence areas. <br />Subsidence cracks, which were observed in soil and weathered bedrock during the 2003 field <br />study within the areas of mining influences of mined-out longwall panels 13, 13A, 14, and 15, <br />are less visible than last yeaz, or there is no longer any trace of them. The processes of <br />weathering, erosion, and infilling have completely healed and sealed most of them. <br />Subsidence cracks and bulges in softer sandstone above mined longwall panel 13, which were <br />abundant during mining in 1999, are less evident than they were in 2003. With the exception of <br />one small, nearly obliterated crack, no cracks were observed during this visit. The cracks heal in <br />831-032.640 Wright Water Engineers, Inc. Page 1 <br />September 2004 <br />