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Ms. Christine Johnston <br />Mountain Coal Company <br />Page 13 <br />April 14, 1997 <br />General Character ojMCC's Ceotechnical Response to Comment #7/ <br />MCC, Golder Associates (MCC's design and geotechnical consultant), and the Division <br />met in January to discuss the Division's adequacy comments. During that meeting MCC <br />and Golder presented their opinion that the slope stability challenges within Sylvester <br />Gulch were less severe than the Division feared and could be managed by appropriate <br />engineering accommodation. <br />MCC has now submitted additional information to support that opinion. They have <br />included a selection of earlier geotechnical investigations of Sylvester Gulch, performed <br />by a selection of geotechnical and geological consultants under their employ, most <br />familiar to the Division, for the Division's information. Apparently some of these <br />materials, not submitted in duplicate, are not intended by MCC to be made a portion of <br />the record. Also in response to the Division's suggestion, MCC has submitted one full- <br />size copy of its Request for Proposal contractor's drawings for the construction of the <br />proposed facilities. A reduced version of this RFP package was submitted in duplicate, <br />appazently for inclusion in the record. <br />As detailed here below, MCC's response provides insufficient additional technical <br />information to warrant the Division amending it's earlier adequacy opinion. The RFP <br />package does assist by providing more detail regazding Golder Associates proposed design <br />treatments for some of the slope stabilization challenges identified at the SGFA site. <br />While minor differences of interpretive opinion exist within the vazious geotechnical <br />reports submitted for the Division's information by MCC, the authors generally agree that <br />Sylvester Gulch is subject to wide spread slope instability problems and that caze should <br />be exercised in developing the proposed Sylvester Gulch facilities. Further, every <br />consultant, including Golder Associates, recommends that additional reconnaissance, <br />monitoring, or site specific investigations be conducted in order. to complete final design <br />of the various surface facilities. <br />Excerpts from reports submitted jar the Division's consideration. <br />"Slope Stability Assessment Sylvester Gulch" by Envirocon, Inc. - 9/93 & 10/94 <br />Envirocon completed a reconnaissance mapping and included a "Sylvester <br />Gulch Risk Assessment" Map in their report. They delineated areas they <br />believed to be subject to "low risk", "medium risk" and "high risk". <br />They included general recommendations for development of facilities <br />within each of these risk zones. Within medium risk zones they <br />recommended; "Any construction activities in this azea should be safe- <br />guarded with adequate drainage, retaining wall buttressing, and monitoring <br />