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<br />Memorandum to Christine Johnston <br />' October 7, 1999 <br />Page 6 <br />1 September 1 s-Mining and P-e-mining Traverses and Evaluations: <br />j Reexamination of Location 12 of September 1998: Located about 150 ft north of the southern <br />gate roads of longwall Panel 13. <br />• Overburden thickness to the B-Seams is about 1,300 ft. <br />' • Cracks are still locally visible on ridge and through the tank trap for about 170 ft. <br />• Cracks range in width from hairline to 3/8 inch and are up to 8 inches deep. <br />' • Cracks aze narrower and less extensive than they were last year, when there was no <br />extraction mining. Currently the site is located at the edge of the area of influence of the <br />' moving longwall face in Panel 13 (angle from Location 12 to face is approximately 21 <br />degrees). <br />' Location 5. Located at monitoring well So.W-3. <br />• Overburden thickness to B-Seam is about 1,200 ft. <br />' • No cracks were observed between Location 12 (of 1998) and this site. <br />1 • Site is located above projected Panel 13A where there has been no mining. <br />Location 6. Located on the fast ridge northwest of Location 5 where either colluvilun and/or soil <br />is less than a few feet thick or sandstone bedrock is exposed (Figure 5). <br />• Overburden thickness to the B-Seam is approximately 1,200 ft. <br />• Subsidence cracks occur in an area 950 ft long parallel to the ridge and 150 ft wide <br />perpendicular to the ridge. <br />' • Site area is located in the dynamic zone above the moving longwall face in Panel 13. <br />Cracks tend to be the widest in this zone, but also tend to close when the face moves out <br />I of the azea of influence ofthe observation site (Figure 5). <br />• The cracks, which are not visible where the colluvilrrn and soil is greater than about 2 ft <br />' thick, aze estimated to be less than 10 feet deep. Some of the cracks in thin colluvium are <br />beginning to heal, even though they are only a few days to a week old. <br />' Wright Water Engineers, Inc., 2490 W. 26'" Avenue, Ste. 100A, Denver, CO 80211 <br />Tel. 303/480.1700; Fax. 3031460.1020, e-mail:knvright@wrightwater.com <br />