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<br />-. <br />,. <br />Pete Evans -2- August 12, 1980 <br />the surface of the pile, (6) a state-of-tlte-art mathematical <br />analysis of the waste pile's slope stability, and (7) proposed <br />inspection/certification schedule and schemes for the embankment. <br />Slopes in the area of the IVestmoreland coal mine demonstrate <br />extensive slope stability problems. Ceomorphi.c surficial features <br />indicate numerous past generations of mass movement. Any stability <br />analysis of the Orch;ird Va]]ey mine backfill situation should <br />specifically treat the topic of foundational slope stability and <br />the influence oP the imposition of the waste pile loads upon the <br />natural slope. A complete geotechnical analysis of the situation <br />should include subsurface sampling and observations within the <br />disposal area. <br />Page 29 of Section 30 CFR Part 784.12, contained taithin Volume I <br />of the application, states that "only underground development <br />waste and excess spoil is disposed of in the area." Based upon <br />this limited material information the proposed waste disposal pile <br />would qualify as a valley fill for the purpose of disposing of under- <br />ground development waste and excess spoil. The application should, <br />therefore, conForm wit}t the requirements and specifications of <br />permanent OSD1 regulations Section 30 CPR 817.71 and 817.72. <br />Stibsidencc <br />The application and subsequent submission in response to state and <br />OSt<1 requests detail a proposed subsidence monitoring plan for the <br />Orchard Valley mine. 'fhe application in its amended form conforms <br />with requirements of the proposed permanent Colorado Program <br />regulations except that subsidence monitoring be completed on a <br />semi-annual basis. A copy of the proposed Colorado permanent <br />regulation subsidence section is attached for the applicants <br />information. <br />JP:mab <br />cc: Rick Mills <br />Attachment <br />. ~~G , ~I <br />