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<br />r ,~,,,,~ <br />MEMORANDUM <br />To: Christine Johnston <br />Mountain Coal Company, LLC <br />~ , From: Wright Water Engineers, Inc. R <br />C. Richard Dunrud, P.E. ~CF~V~o <br />Date: October 7,1999 - oCj 13 1998 <br />..~.~„~,M.~~y~G <br />' Re: Subsidence Field Observations- September 15-17, 1999 ~Y <br />Summary of Major Findings <br />1. No new cracks attributed to subsidence were observed above longwall Panel 10 in azeas <br />where cracks, at least partly attributable to subsidence, were observed last yeaz. The <br />cracks observed last yeaz were healed and not discernable, except for some cracks due to <br />mass-gravity movements in the crown of the topsoil pile and along the drainage ditch west <br />ofthe topsoil pile. <br />' 2. In the Apache Rocks Permit Area, smaller cracks were observed at revisited sites this yeaz <br />than were observed last yeaz. Last year [here was no longwall extraction beneath these <br />azeas. This year many of these revisited sites had been undermined. <br />3. Subsidence cracks were observed in bedrock and also in colluvium and soil less than 2 ft <br />thick on a ridge above Panel 13 in the Apache Rocks Permit Area. Cracks were not <br />observed in this area where the colluvium and soil was greater than 2 ft thick. <br />' 4. No new cracks were observed in the landslide terrain on the north side of Jumbo <br />Mountain. Dry conditions during last winter and eazly spring reduced water lubrication <br />that can renew slide activity. The wet periods during the late spring and summer <br />apparently did not provide saturation deep enough to cause renewed sliding. <br />5. Large, open pre-mining fractures as much as 2 feet wide were observed in sandstones of <br />the Ohio Creek Member of the Mesaverde Formation on West Flatiron neaz cliff edges. <br />Cracks were also locally observed on the narrow portions of West Flatiron. These cracks, <br />which aze present prior to mining, aze the result of lateral spreading due to natural mass- <br />gravity forces acting in cliff azeas of reduced lateral constraint. <br />Wright Water Engineers, Inc., 2490 W. 26'" Avenue, Ste. 100A, Derner, CO 80211 <br />Tel. 303/480.1700; Fax. 303/480-1020, e-mail:knvright@wrightwater.com <br />