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1 <br />Memorandum to Henry Barbe <br />September 27, 2000 <br />Page 2 <br />across the 320-foot-wide affected area, total extension in the sandstone outcrop <br />ranges from 0.75 to 1.5 feet. Assuming that nearly all the tensile strain in this brittle <br />sandstone is reflected as cracks-which the author considers a reasonable <br />assumption-the tensile strain is calculated to range from 0.23 percent to 0.47 percent <br />(0.0023 to 0.0047 ft/ft). This range is well within values projected in Exhibit 60. <br />5. The subsidence cracks above the east boundary of longwall panel 12 at Apache Rocks are <br />located in an area of permanent to semi-permanent strain. In contrast to the temporary <br />' strain condition described above longwall panel 13 (Item 3 above), these cracks may <br />remain open for many years. However, due to the flexural slip process that occurs during <br />downwarping of multiple lithologic plates, the tensile strain in the sandstone unit (where <br />' the cracks are visible) will progressively narrow and change downward into compression. <br />This process of flexural slip deformation is well known and documented in structural <br />engineering and geology-the tension above the neutral surface changes to compression <br />' below the neutral surface of material behaving as a beam or a plate. <br />OVERVIEW OF FIELDWORK FOR AUGUST 28-30, 2000 <br />' 1. Mountain Coal Company (MCC) provided anall-terrain vehicle (ATV) for transportation <br />efficiency. On August 28, David Nicewicz, of West Elk Land Surveying, and 1 traversed <br />the six cross section locations in Deep Creek that are located near the eastern part of <br />longwall panels 14 through 17. On August 29-30, I made additional ATV and foot <br />traverses alone above panels 14 through 17 and 12, 13, and 13A. <br />' 2. Based on field knowledge of subsidence processes, the areas and sites traversed were <br />selected to obtain the most subsidence information. Selected video images that show <br />major subsidence features are included in this report. <br />3. The traverses, sites, and areas were visited in the following chronological order (see Map <br />1, location map, for details): <br />August 28 (observations made with David Nicewicz): <br />1. Pre-mining subsidence evaluation traverse of cross sections 1 through 6 in Deep Creek <br />neaz the eastern pazt of longwall panels 14 through 17 by ATV. <br />' August 29 (observations made alone): <br />' 1. Pre-mining subsidence evaluation traverse by ATV above the central to western parts of <br />longwall panels 14, 15, 16, and 17 in the southern part of West Flatiron, the head of <br />Sylvester Gulch, and the head of the first west fork of Deep Creek south of West Flatiron. <br />2. Traversed by foot the southeastern ridge of West Flatiron above the east-central part of <br />longwall panel 14, using apace-and-compass method of traverse location. <br />' Wright Water Engineers, Inc., 2490 W. 26°' Avenue, Ste. 100A, Denver, CO 80211 <br />Tel. 303/480-1700; Fax. 303/480-1020, e-mail:krwright@wrightwater.com <br />