Laserfiche WebLink
Fall 2014 Subsidence and Geologic Field Observations <br />South of Divide and Dry Fork Mining Areas <br />2.0 SUMMARY OF FALL 2014 FIELD STUDIES <br />Observations of the SOD and Dry Fork mining areas have been made annually in the active or <br />recently completed mining areas since 1996 and semi - annually since 2007 to assess potential <br />longwall mining effects on the environment. On October 4 and 5, 2014, WWE performed <br />subsidence and geologic field investigations of the SOD and Dry Fork mining areas for MCC as <br />the second part of the 2014 field activities. An attempt to complete field activities during the prior <br />week proved unsuccessful due to recent rains. <br />Based on the field observations to date, the overall effects of longwall mining have been less than <br />initially projected. Nineteen years of experience (1996 to 2014 inclusive) indicate that subsidence <br />features (cracks and bulges) are most visible on roads and trails, where the ground is more compact <br />and free of vegetation. These areas (or traverses) are targeted for specific observations either on <br />foot or using a 4 -wheel drive vehicle. In addition, photographic comparisons are routinely made <br />to evaluate and document changes between observations (using regularly visited photographic <br />observation points) and to record their condition for future reference (Maps 1 and 2). <br />Subsidence - related tension cracks were observed during our fall 2014 field visit to the SOD and <br />Dry Fork mining areas along some drill roads accessed by U.S. Forest Service Road 711 (Dry Fork <br />Road) and on methane drainage well (MDW) pads, particularly where they exist above active <br />mining locations. In general, subsidence - related tension cracks observed in previous site visits <br />were noticeably weathered and less discernible. <br />Longwall mining in the SOD and Dry Fork mining areas were initiated at the east end of E -seam <br />Longwall Panel E1 in December 2008. At the time of our fall 2014 field visit, mining was <br />complete on E -seam Longwall Panels E1, E2, E3, and E4 and was approximately 30% complete <br />on E -seam Longwall Panel E5. Subsidence related features were observed at the surface along <br />Traverses C -C', E -E', F -F', I -I', and J -J'. Observed subsidence related features were generally <br />expected either at previously observed locations or in an area of relatively recent longwall mining <br />activities (i.e., areas of maximum expected dynamic subsidence effects). Additional details <br />regarding the observed subsidence features can be found in Sections 3.2, 3.5, 3.6, 3.12, and 3.15 <br />of this report. Baseline observations of MDW pads and access roads were completed above the <br />middle to western end of unmined E -seam Longwall Panel E5. <br />831 - 032.796 Wright Water Engineers, Inc. Page 5 <br />March 2015 <br />