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MOUNTAIN COAL <br />~COMPANYL.L.1:. <br />A 5ubsidiar}' of Arch W<slem R<snurcu, LLC <br />February 10, 1999 <br />Mr. Jim Burnell <br />DECEIVED <br />FEB 16 1999 <br />Colorado Division of Minerals and GeologKyy <br />1313 Sherman Street, Room 215 ""~'un otNllnerals 6 Geology <br />Denver, CO 80203 <br />III IIIIIIIIIIIIIIII <br />999 <br />Wes[ Elk Mine <br />P O nac 591 <br />5174 Highway 133 <br />Somerset C'O 81434 <br />(970)929-501? <br />a ll Fug (970) 929-5595 <br />RE: Technical Revision No. 87 (As-built of ROM Expansion); West Elk Mine; <br />Permit No. C-80-007 <br />Dear Jim: <br />Mountain Coal Company, LLC (MCC) has reviewed the Division's adequacy letter dated February 9, <br />1999 for the above-referenced technical revision application. To reiterate from the application package, <br />during the soils and foundation investigation nor during actual construction, no groundwater was <br />encountered in the foundation materials. The probability that the pad expansion will somehow now <br />become saturated is extremely low, because the fill was constructed with a maximum one-foot lift and <br />was well compacted. The mean compaction was 95.8 percent (modified Proctor density value). More <br />importantly, a rock underdrain was constructed at the bottom of the fill to prevent potential ground water <br />pressures beneath and within the pad fill. In addition, MCC constructed an upland clear water diversion <br />to divert s[ormwater/runoff away from the pad. Therefore, MCC does not expect the till to become <br />saturated. As such, MCC believes that non-saturated soils and foundational bedrock assumptions of the <br />stability analysis completed by Barr Engineering were appropriate. Nonetheless, MCC agrees that <br />monitoring should occur to document that the unsaturated condition continues, but disagrees that <br />piezometers and profile lines should be installed. Instead, MCC proposes the following: <br />Utilize the rock drain outlet as a monitoring point. If any water is beneath or within the fill, it will <br />Flow through the rock drain. <br />2. Install a survey mirror station on the outslope of the pad that will be monitored along with all other <br />survey mirrors located around the mine site. <br />Please call if you have any questions. <br />i erely, <br />ris[ine E. Johnst <br />Permitting Special, <br />cc: Eric Mende <br />Phil Schmidt <br />Earl Quesenberry <br />Kathy Welt <br />rr87a.doc <br />