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• 43. OCM proposes the use of berms to divert disturbed area runoff the sedimentation ponds or other treatment structures. DMG is concerned that berms will not be as effective as ditches, in that the berms would likely be eroded by water. Ditches would be cut subgrade into bank or compacted material, whereas berms would be loose, porous material which could become saturated and fail. Unless OCM has additional information which would demonstrate that the berms would be more effective tJ~an ditches, DMG does not believe they are the best technology currently available, and accordingly could not approve of their use as OCM has proposed. Response: Oxbow has successfully utilized berms for many years in relatively flat areas and low energy environments to both meet MSHA requirements far roadside safety berms and to intercept and route disturbed area runoff (ie: existing southern perimeter berm paralleling railroad and berms along overland conveyor line). In certain areas where space is limited (ie: not sufficient room for both a safety berm and a ditch) or where containment must be assured, berms may represent the best available control technology. Drainage designs reflecting the use of berms have been reviewed to determine if ditches would be more appropriate for any given drainage control application and to evaluate erosion potential. The drainage design documentation presented in Appendix B and on Map 3211 has been revised or expanded as appropriate to reflett the use of ditches if they are more appropriate than berms and, if not, to justify the use of berms and verify that excessive erosion will not be a problem. Please see accompanying revisions. 44. The postmine plan calls for "low maintenance dry crossings" where ditches cross roads. Please provide design information for each crossing which demonstrates that water will be contained in • the crossing. Response: Dry crossings will essentially be widened ditch sections with reduced sideslopes for road approaches on either side, additional large diameter and graded tiptop materials in the crossing area to provide a stable road base, and transitional sections to blend smoothly with the ditch configuration both upstream and downstream of the crossing. A drawing of atypical dry crossing has been added to Appendix B co graphically illustrate the crossing concept and configuration. Please see accompanying revisions. 45. The application narrative and data (pp. 2.04-39f and •3981 indicate that the 6 ephemeral drainages which could be affected by the West Valley Fill have not exhibited flow since January 1995. Were the drainages visited during or shortly after rainstorms? If not, OCM need to obtain data during precipitation events to determine whether and how much the drainages would flow in response to precipitation. Regardless, the monitoring data should be annotated to indicate weather conditions at the time of each observations. The application states, on page 2.04-39e that the flow data are presented on pages -39g and -39h. The data are presented on -39f and -39g. Response: Please refer to previous Response 9 above. The discussion of Flow monitorinf has been revised to correct the page references as noted. Please see accompanying revisions. 46. A worksheet in Appendix Cshows the calculations used to size the haul road ditches. From where did OCM ascertain the 3.9 cfs flow value? We are unable to locate any supporting information • for the value. Responses: Given previous DMG comments (ie: Comments 26 through 36) relative to the drainage designs for the West Valley Fill and associated haul road, all drainage designs for these areas have been reviewed and revised as appropriate. The drainage design