REP42703 - Laserfiche WebLink

Home Browse Search

SPRING 2007 Subsidence and Geologic Field Observations Box Canyon, and South of Divide Mining Areas Soil and colluvium as much as 10 feet thick, derived from clays and silts of the Wasatch Formation and the underlying Ohio Creek Member of the Mesaverde Formation, were encountered on the road. Several cracks were noted in 2006 and again visited in the spring of 2007 above the northeastem edge of mined longwall panel 19, on the northern edge of drill pad for MDWs 19-01, 19-02, and 19-03 (Location 4). New cracks were noted both in the drill road and in the MDWs 21-32, 21-36, and 21-38 drill pad area (on the west side of the road) over the northeast corner of unmined longwall panel 21 (Location 5). 5.3.1 Location 4 In 2006, cmcks were observed above the northeastern edge of mined longwall panel 19, on the northern edge of MDWs 19-01, 19-02, and 19-03, in graded material. Based on their location, these cracks were within the area of maximum tensile strain. The overburden depth to the B- Seam in this area is about 2,250 feet. The drill site is constructed primarily in soil and colluvium derived from the Wasatch Formation. Observations made during the spring of 2007 (Figure 10) show that considerable healing of these cracks has occurred. In fact, the actual location of the cracks would not have been possible without referencing their position from the 2006 photograph (Figure C-3). These particular cracks are thought to be related to either differential settlement of the graded material and/or to subsidence. At this time it is still unclear which potential explanation is the most accurate or probable. It was previously estimated that the probability of the cracks being settlement related versus subsidence related was about 50/50. Observations made during this most recent site visit have not changed that probability. . 831-032.780 Wright Water Engineers, Inc. Page 17 July 2007