2015-03-17_REPORT - C1980007 - Laserfiche WebLink

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Fall 2014 Subsidence and Geologic Field Observations South of Divide and Dry Fork Mining Areas E6 (see Maps 1 and 2). The E -seam overburden depth along this traverse varies from slightly less than 700 feet to almost 900 feet. Subsidence features had previously been observed along the northern portion of this traverse dating back to the spring of 2012 during mining of E -seam Longwall Panel E3. At that time, subsidence features were noted on both sides of the road parallel to Dry Fork near the turnoff to the MDW E3 -29 pad, along the access road to MDW E4 -11 across Dry Fork from the MDW E4 -12 pad and in the cut -slope above the access road where it meets the MDW E4 -11 pad. No evidence of these subsidence cracks could be identified during the fall 2014 field visit. The southern portion of this traverse (south of Dry Fork) currently provides access to five MDW pads including E4 -12, E4 -13, E4 -14, E5 -15, and E5 -16 (see Map 1). At the time of our fall 2014 field visit, each of the pads overlying E -seam Longwall Panel E4 had been undermined. No subsidence features were noted on MDW E4 -12 and E4 -13. Previously - observed subsidence cracks on the MDW E4 -14 pad are still present (see Figure 5) but more subdued, showing considerable sediment infill and rounding of edges. Subsidence cracks along the access road to this pad were no longer evident but cracks on the hillside above and to the west of this road were still apparent. Traverse F -F' continues southward up Poison Gulch across unmined E -seam Longwall Panel E5 and E6. This traverse passes USFS Water Resources Pond P95 (see Figure 6). Near this pond, a new access road has been constructed leading west and then north to a large pad for MDW E5 -16. This pad showed no signs of subsurface instability (due to mining of E -seam Longwall Panel E4) or differential settlement. 831 - 032.796 Wright Water Engineers, Inc. Page 11 March 2015