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MEMORANDUM <br />To: Christine Johnston <br />Mountain Coal Company, LLC <br />From: Wright Water Engineers, Inc. <br />C. Richazd Dunrud, P.E. <br />Date: November 19, 1998 <br />Re: Subsidence Field Observations-September 1998 <br />Summary of Major Findings <br />During the course of the studies, some expected and some new information was obtained in <br />relation to (I) deformation within the angle of draw of coal extraction panels (2) subsidence <br />cracks, (3) crack potential along the old road up Sylvester Gulch as a result of longwall face <br />advance, (4) cracks that look like they are related to mining, but probably are caused by some <br />natural process-such as a type of mass-gravity spreading perhaps initiated or amplified by the <br />desiccation process, and (5) landslide cracks and bulges, that were thought to have been <br />somewhat influenced locally by mining during the investigation in August 1997, are now thought <br />to be influenced even less by mining during the September 1998 stuvey. <br />1. Amine dewatering well that has exhibited some downhole deformation was observed 300 <br />feet north and 350 feet east of the northeast comer of Panel 10 and is located within the <br />angle of draw of Panel l0. High sheaz stresses commonly are generated at stratigraphic <br />boundaries due to flexural slip along these boundaries as the strata undergo differential <br />vertical displacement in response to the subsidence process. <br />2. Cracks believed to be mine related were observed in an area above the northern boundary <br />and northeast corner of longwall Panel 10 where tensile strains would be expected to be <br />greatest. The surface area is locally free of brush and is quite accessible for observation. <br />The cracks ranged in width from about'/< in to 1 in, ranged in depth from a few inches to <br />perhaps 2.5 feet, and ranged in length from a few feet to about 100 feet. <br />3. No cracks were observed on the old road above Panels 10 and 11 in areas where the <br />longwall face passed below. As is commonly the case, cracks tend to open, as the face <br />moves to within its area of influence and then close again as the face passes out of the azea <br />Wright Water Engineers. Inc., 2490 W. 26'" Avenue, Ste. 100A, Denver, CO 80211 <br />Tel. 303/480-1700; Fax. 303/4841020, e-mail:krxnght@wnghtwater.com <br />