Laserfiche WebLink
Memorandum to Henry Bazbe <br />September 27, 2000 <br />Page 1 1 <br />' pattern like desiccation cracks. The dam appeazs to be stable, because the cracks are <br />shallow and do not cut through the dam. <br />t • The cracks look more like desiccation cracks than subsidence features, because of their <br />irregular pattern. However, the irregular pattern may be the manner in which the dam, <br />consisting of silty clay material, responds to more regular cracking in bedrock below the <br />alluvium. There may be a subsidence component to these cracks, because the longwall <br />face is located (as of 8-30-00) beneath the dam area. However, because there were no <br />' other cracks observed in the traverse along acattle/game trail to point 15A, the <br />subsidence component of the cracks relative to the desiccation component may be equal <br />to or less than 40 percent/60 percent (subsidence/desiccation less than or equal to 40 <br />' percent/60 percent). <br />• The pond is dry, but all the ponds observed in the area are dry because of the very dry <br />spring and summer this year. <br />Location 16. Located 1,000 feet southward along drill road from the main road near <br />' Apache Rocks. It is located at the northern part of an area of cracks that <br />extends southward roughly 100 feet, and is located above the approximate <br />mid-point of mined-out longwall panel 13. <br />' • No subsidence features were observed during an ATV-traverse of the drill road between <br />the main road neaz Apache Rocks and Location 16. <br />' • Point is located in thin silt-clay soil, colluvium and sandstone. Projected overburden <br />depth to the B-seam is 1,300 feet. <br />' • Subsidence cracks are as much as 1'/~ inches wide, 70 feet long, and trend N20°E to N-S <br />and also N20°W (see Figure 4). <br />' Location 17. Located at Drill Hole SO.W-3 and also observation Location 5 of September <br />16, 1999. Point is located above panel 13A, where only development mining <br />has been done. Projected overburden thickness to the B-seam is 1,200 feet. <br />• No cracks were observed at this point. No new cracks were observed during ATV <br />' traverse along drill road above mined-out longwall panel 13 from Location 16 to <br />Location 17. <br />• Fewer cracks were observed from Location ]6 to Location 17, now that extraction mining <br />has been completed, than were observed in 1998 when no extraction mining had yet been <br />done. Only one crack, '/< inch wide and about 6 feet long, was observed in a tank trap. <br />This is the same crack that was observed in September 1998 (observation point 12), but it <br />is now less extensive and is nearly healed. <br />' Wrighl Waler 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 />