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,:. <br />Ms. Paige Seville -5- December 17, 1984 <br />• <br />clay exists beneath the F-seam and that unique differential consolidation <br />related phenomena have resulted in the development of open penetrating roof <br />cracks in areas of the mine underlying the proposed waste pile site. <br />For all of these reasons, the Division believes it is appropriate to <br />require the operator to complete an analytical determination of the effect of <br />the proposed waste pile's construction upon lateral stability of the F-seam. <br />The specific task posed is to determine whether the imposition of the 9 <br />million ton load might precipitate a lateral failure within the partially <br />extracted F-seam. <br />3. The applicant proposes the construction of a 2500' length of 30' wide <br />haul road to be used to transport waste to the pile for placement. However, <br />the design information contained within the permit revision application is <br />limited to a brief discussion and a map exhibit. Slope stability problems <br />have been encountered throughout portions of the existing surface facility <br />area's road cut slopes and fill embankments. For this reason, the Division <br />believes it appropriate to require more thorough design information regarding <br />,!)'~P~ the geotechnical specifics of the proposed road corridor. The applicant <br />should provide cross-sections on an appropriate station frequency, such as <br />• 200'. Worst case representative cut slope and embankment fill sections should <br />be analyzed to determine whether artificial slope reinforcement or subsurface <br />moisture drainage will be necessitated. As in analogous situations regarding <br />the existing surface facilities, the design analyses should include stability <br />and drainage considerations of both the operational and proposed reclaimed <br />haul road configurations. <br />4. The application correctly observes that the stability of the waste <br />structure might be critically affected by infiltration of waters, resulting in <br />increased pore water pressure ratios. Therefore, the applicant appropriately <br />proposes the installation of coarse aggregate backfilled trench subdrains. <br />However, the design and construction specifications presented for these <br />proposed subdrains are inadequate. The applicant should include a projection <br />of the maximum flow to be accommodated by these subdrains. Further, the <br />applicant should provide complete size gradation specifications for the <br />subdrain aggregate material. Using that specified gradation, the applicant <br />should demonstrate the adequacy of the cross-section of these proposed <br />subdrains to accommodate the expected maximum flows. In addition, the <br />applicant should elaborate upon the stated intention to obtain on-site <br />materials of suffi er gradation to meet the require <br />materia specifications. The application observes that a filter fabric will <br />be used to cover the completed drain. The Division believes that the <br />aggregate drain should be enveloped in geotechnical filter fabric, in order to <br />~-~~ assure maintenance of the necessary effective cross-sectional area and <br />prevention of fine material invasion. <br />5. The application states that inspections of the waste structure will be <br />performed on a quarterly basis. The Division, through reference to Rule <br />4.09.1 from Rule 4.10.1(1)(a), requires that inspection also be performed <br />during specific critical periods; such as "(1) removal of all organic material <br />and topsoil, (2) placement of underdrainage systems, (3) installation of <br />surface drainage systems, (4) placement and compaction of fill materials, and <br />