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<br />999 <br />51 nT4 Cn' r]t>i ,,,unUi~ ,n, n.v a, ~~. i n•r.~ ,. •.• •~•., <br />D EPARTMtNT OF NATURAL RESOURCES <br />D. Monte Pascoe, Execm rve Dlrec wr <br />iti11N LU LAND R ECLA~1 AT1ON <br />423 Centennial Building. 1313 Sherman Street <br />Denver, Colorado 80203 Tel. (303) 839-3567 <br />David C. Shelton <br />Director <br /> <br />M E M O RAN D U Al <br />30 October 1981 <br />TO: Tom Gillis <br />FROM: Jim Pendleton - ~~~ <br />~:. ~-.-^ <br />RE: Supplemental Stabil;ity and Subsidence Submissions for <br />/ B1ue~Ribbon Coal Mine <br />Pursuant to your request, Z have reviewed the supplemental materials <br />submitted by Western Associated Coal Corporation for the Dlue Ribbon Coal <br />Mine. I forward the following cormnents for your consideration. <br />Portal and [/elI Sealing: <br />The sealing techniques descriptions and drawings are acceptable, <br />with one deficiency in the companys' presentation. 7'he operator fails to <br />discuss whether mine drainaye will occur at the location of the portals <br />following reclamation and sealing. The hydrology section should be amended <br />to specifically discuss this topic. <br />Portal Bench and 1lighwall Stability: <br />The supplemental materials contain discussions of both operational and <br />backfilled portal bench and highwalZ slope stability. The applicant and <br />the applicants' consultants both recognize the existence of a slope <br />instability problem on the portal bench facial slope. The applicant has <br />submitted a remedial plan to eliminate this problem in response to an <br />inspection notice of violation (October 22, 1981 letter by Ute Engineering <br />& Surveying Company). This design includes installation of a perforated <br />interceptor drain rile and a regrading of the bench surface, both intended <br />to decrease infiltration of moisture into the bench which the applicant <br />believes is the cause of the problem. The applicant further commu:ts, in <br />the amended application, to the completion of appropriate geotechnical <br />and stability analyses and the installation of three standpipe piezometers <br />to monitor the phreatic surface and degree of saturation of the portal <br />bench. This proposal and the applicants' indication of completion of the <br />remedial construction by February of 1982 can be approved inunediately <br />in order to expedite correction of the problem and completion of the <br />geotechnical analyses. <br />The amended application also commits the applicant to completion of <br />a stability analysis of t/re proposed final backfilled configuration, <br />including shear strength testing and definition of the phreatic surface. <br />The application incorporates a request for variance from AOC based upon <br />the existence of steep slope mining conditions within the portal area. <br />