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permanent drainage system for the refuse pile. Given the potential <br /> for blockage and maintenance requirements associated with a <br /> culvert, a designed surface diversion would be more appropriate. <br /> The final drainage configuration needs to be incorporated on Map <br /> 6C, and diversion designs and supporting calculations need to be <br /> submitted. <br /> 2 . Map 6B does not depict the culvert extending from the parking <br /> structure located by the mine office to Pond 8 , or the flexible <br /> pipe extending from beneath the raw coal conveyor to Pond 8. All <br /> drainage control structures and conveyances in the South Portal <br /> facilities area should be depicted on the map. <br /> 3 . Appendix X "Sediment Control Plan" makes reference to a <br /> Roadside Refuse Pile upper catch ditch and lower catch ditch. No <br /> upper catch ditch is depicted on Exhibit 6B, which shows only a <br /> lower catch ditch No. 1 and lower catch ditch No. 2 . Please <br /> address this apparent inconsistency, and update the map and <br /> appendix as necessary. <br /> 4 . Map 8B and page 168 of the permit application make reference <br /> to the North Portal east and west collection ditches, but <br /> supporting drainage calculations for these ditches are apparently <br /> not included in the Division's copy of the permit application. <br /> Please submit supporting calculations for these ditches. <br /> 5. During site inspections, an inlet pipe on the north side of <br /> Sediment Pond 5 has been noted that is not depicted on Exhibit 8B. <br /> Please amend Map 8B to include this pipe and provide supporting <br /> calculations. <br /> 6. The Division has previously approved a variance from the 20 <br /> year/24 hour . design requirement for the two upper Coal Creek <br /> reinforced concrete dip-sections which each have six 36 inch <br /> culverts, which in aggregate have an end area greater than 35 <br /> square feet. This variance from the requirement of Rule <br /> 4 .03 . 1(4 ) (e) ( i ) was based on certain assumptions set forth in the <br /> Division's June, 1993 Findings of Compliance. Assumptions were <br /> that any overtopping would likely be a gradual event with very <br /> little turbulence induced by the dip-section. Inherent in the <br /> approval was the assumption that the culverts would remain open and <br /> flowing during passage of flow which overtops the structure. In <br /> practice, overtopping has not occurred as projected, as the <br /> multiple culverts tend to become obstructed during high flow <br /> events, resulting in more sudden and turbulent overflow which has <br /> on at least one occasion escaped the channel. In light of these <br /> considerations, the Division believes the two upper Coal Creek dip <br /> sections need to be redesigned and reconstructed to comply with the <br /> requirements of Rule 4.03 .1( 4 ) (e) ( i) . Unless a demonstration can <br /> be made that the design assumptions upon which the variance was <br /> granted remain valid, appropriate design revisions will need to be <br /> submitted, and implementation will need to occur within a <br /> reasonable timeframe. <br />