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• -3 • <br />XIX. Mine Facilities (Portal Bench) (2.05.3(3), 2.05.3(7), 4.04) <br />The applicant proposes cut slope and embankment slopes similar to those adjoining <br />the haul road for the portal bench area of the Munger Canyon mine. The portal <br />bench area also constitutes a "steep slope mining area". All proposed fill <br />slopes are to grade at 2:I (horizontal to vertical) and are, therefore, <br />acceptable. Cut slopes proposed within the portal bench area are limited to <br />1.5:1 (horizontal to vertical) in upper colluvial soil materials and 1/4:I <br />(horizontal to vertical) in lower bedrock materials. These cut slopes are <br />in compliance, therefore, with the permanent program regulations. <br />XX22. Sealing of Portals (2.05.4(2)(9), 4.07) <br />The applicant proposes to abandon the portals at the Munger Canyon mine by <br />constructing a 16 inch thick double concrete block wall, keyed a minimum of 12 <br />inches into the floor, roof and ribs. This wall will be constructed at a <br />minimum of 25 feet from the surface. Following completion of the concrete block <br />wall, the remaining portion of the portal will be backfilled with incombustible <br />materials. As such, the proposed technique conforms with the M.S.R.R. regulations <br />as stated in 30 CFR 75-1711, Federal Code of Regulations. This technique will <br />also satisfy the requirements of the permanent regulatory program, assuming that <br />the mine will not produce effluent waters at the portals. I suggest that you <br />clarify this concern with Roy Cox. Roy has preliminarily indicated that drainage <br />will not occur at the portals, based upon information submitted within the <br />application. <br />09, 4.13, 4.1 <br />4(21 (a) . 2.05.4 <br />The applicant's treatment of post-mining topographic configuration and backfilling <br />and grading plans for the Munger Canyon mine are vague, at best. The applicant <br />proposes not to backfill the workings to achieve approximate original contour. <br />The application contains no description or cross-sections of proposed backfilling <br />and grading plans for the haul road or the mine portal bench areas. <br />The upper haul road segment between the confluence of the Munger Creek Valley and <br />the unnamed tributary to the Munger Creek Valley (Sta 67+00') to, and including, <br />the mine portal bench area, is characterized by steep slopes, cozrunonly in excess of <br />200. In order to receive approval for any variance from approximate original <br />contour the applicant must submit an acceptable request for variance from approximate <br />original contour based upon steep slope mining conditions, pursuant to Rule 2.06.4 <br />and 2.06.5. <br />Under the regulations of Rule 9.27, "Operations and Steep Slopes", the applicant <br />is allowed variance of approximate original contour, only if the approximate <br />original contour configuration will not achieve a static slope safety factor of <br />1.3, as required by Rule 4.14. Ideally, the entire highwall shall be backfilled, <br />utilizing a slope configuration which result in a static slope safety factor of <br />1.3. In siturations in which a static slope safety factor of 1.3 cannot be <br />achieved, the applicant should backfill to that configuration which will allow a <br />static slope safety factor of 1.3 for that portion of the backfilled slope. <br />Remaining portions of the exposed cut slopes should be treated to achieve a surface <br />which is as erosionally and structurally stable as is possible. <br />