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TRAPPER MINING INC. PR-2 RESPONSE - 12/8/87 DIVISION COMMENT: Section 3.5 Backfillin and Grading The items not resolved at this time are 6) Maps M-3 and M-12, Pre- and Post- mining topography and 7) Section 3.5.5 Final High walls. The Division's com- ments are as follows: Postmining Topography The postmining maps roust have lines drawn to depict where channels will be constructed. In many instances, it is difficult to [race where Trapper expects [o place a drainage channel due to the fact that valley definition is not presented in all cases. One example is the main branch at Johnson's Gulch from elevations 6,700 to 6,750 feet. At this point, no valley bottom is defined and the cross section through the area is flat. Trapper must delineate [he positioning of the channel and also revise the postmining map to include valley definition in this area. Many haul roads still exist on the postmining topography maps making the final configuration of the postmining topography difficult to extrapo- late. All roads not approved as permanent must be removed from the post- mining topography maps. Johnson's Gulch The drainage density reconstuction proposed for the Ashmore Pit area of Johnson Gulch is much less than originally approved and less than the premising density. A maintenance of drainage density from the premising to the postmining is essential to ensure topographic and channel stability. This is especially true in the case of Johnson's Gulch where the premising land cover is greater than the proposed postmining land use cover will achieve. Trapper must revise this area [o allow for greater drainage density than is now proposed or else present a hydrologic study discussing how the present density will be stable. Several more specific problems have also been cre- ated by the lack of drainage density through the lower portions of Johnson's Gulch. One channel section in the undisturbed area has been cut off with no defined drainage below it. This undisturbed drainage exists through the locations N 406,500 and E 1,419,100. This channel section does not have a defined drainage proposed north of the 6,750 foot contour elevation. This drainage must be con- tinued. The natural continuation of this channel would be underlain by the long term ash disposal site. A revision to either the ash pit location or a relocation of [he natural stream continuation will need to be accomplished. The eastern-most long term ash disposal site is overlain topographi- caLLy on the proposed postmining contour maps by a Low or what appears to be valley definition. This low area will need to be removed to ensure that surface drainage does not occur over the [op cont.