2017-01-25_REPORT - C1980007 - Laserfiche WebLink

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Fall 2016 Subsidence and Geologic Field Observations South of Divide and Dry Fork Mining Areas Previous observations of subsidence cracks were described along this traverse on the MVB E5-20 pad beginning in the Fall 2015 Subsidence Report. Details associated with the fall 2016 observation of these subsidence cracks are provided below as Location 1. No other subsidence -related features were observed along this traverse during our fall 2016 field visit. 4.2.1 Location 1 Location 1 is on or near the MVB E5-20 pad. The first observation of subsidence features on the MVB E5-20 pad occurred during our fall 2015 field visit (approximately one month after longwall mining passed beneath this area). Observations made at that time found four large, parallel subsidence cracks oriented in a N5°W direction with a offset spacing of between approximately 10 and 40 feet. The first of these cracks was located on the access road approximately 30 feet east of the pad. The second and third cracks were located where the access road joined the pad (see Figure 1). At that time, the maximum length of the western crack was a nearly continuous 135 feet, with the crack ending on barren ground north of the pad. This pad was noted to have a maximum width of 14 inches and maximum depth of about 6 feet. The E -seam overburden depth at this location is 450 feet. Observations at the MVB E5-20 pad during the fall 2016 field visit found continued evidence of the subsidence cracks but with notable weathering as represented by rounded crack edges and sediment infilling. Figure 2 shows the subsidence cracks on the E5-20 pad as observed during our fall 2016 field visit. Continued healing and sealing of these cracks has diminished their appearance by rounding the edges and reducing the crack depth. Some widening of the cracks was noted in response to edge deterioration and slumping into the openings. 831-032.798 Wright Water Engineers, Inc. Page 11 January 2017