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Christine Johnston, MCC November 19, 1998 Page 8 Location 16. Located at what is known as ttte "Wet Meadows" area where a flow of ~ to i0 gpm was observed on August 6, 1997. • The area is now completely dry; some flow observed by Ron Hanna in May 1998 and damp in June 1998. The azea was very wet in June 1997. • Area ~ppeazs to have been dry this year for a considerable period of time. CDMG-8 Located in steep landslide topography above longwall Panel 8 about I50 feet north of the chain pillazs between Panels 8 and 9. Cracks parallel and cross the road: • Trend N35°E, as much as 2 1/1 feet wide, 6 feet deep, and about 125 feet long. • Trend roughly E-W, as much as l % feet wide and 4 feet deep. • Relatively new cracks occur among alder cracks. Conclusions The major and perhaps most important conclusion stems from cracks that apparently aze not related to mining. Many of the cracks observed above two areas south of the B-Seam Mains, i.e. Locations 9, 10, and I 1 and Location l2, are larger and as extensive as the cracks above the northeast corner of longwall Panel 10. This suggests that there may be natural processes at work, such as mass-gravity spreading and desiccation, that can impact the ground surface and near- surface hydrology as much or more than subsidence caused by longwall mining. As mentioned in the Summary of Major Findings, tensile strains aze likely to be highest above the corners of extraction panels because wrap-azound stress concentrations (i.e. comer stressesk However, these cracks are smaller and/or less extensive than many of the cracks observed at Locations 9 through l2, where longwall mining has not yet occurred. Another major conclusion reached in the study of the Jumbo Mountain surface cracks is that many or most of the cracks aze likely only landslide related. Large, extensive cracks only a few weeks to a few months old were observed during this trip in obvious landslide areas (as evidenced by htunmocky topography, trees leaning in all directions, and ponds) above longwall Panels 8 and 9. However, mining in Panels 8 and 9 was finished in August 1996 and April 1997, respectively, beneath these areas. Also, large cracks only a few weeks or months old were found neaz or among cracks observed by CDMG in 1996 and by Dtutrttd and Nicewicz in August 1997. The fact that there were no cracks observed on the Sylvester Gulch road above Panels 10 and I l (excluding the area of possible, but unlikely, subsidence cracks above the dividing chain pillars) attests to the process observed by the author in other mining azeas. Tensile strains created by the passing of the longwall face are also relieved once the longwall face moves out of the area of mining influence. Wright Water Engineers, Inc., 2490 W. 26'" Avenue, Ste. t00A, Denver, CO 80211 Tel. 303/480-1700, Fax. 303/480-1020, e-mail:krwright@wrighhvater.com