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i'1. •~ Memo - Grassy Gap File Provide a schedule to install east of Pond 4 this summer per the remaining material balanc -2- and reclaim to a 3:1 the October 8, 1990 e required to achieve April 16, 1991 back slope the area submittal. Document reclamation of Pond 4. Response to Question 7 and the Sedimentology Portion of Attachment 2: 7. The Division accepts the methodology utilized in performing the sedimentation analyses, but rejects some of the assumptions. We are unable to evaluate the results of this section until the following assumptions are modified: a. The response to question 7 indicates that vegetative cover values representative of pre-mine conditions were used, yet the sedimentology analysis uses cover values from the sagebrush reference area. The Division agrees with the use of the sagebrush reference area but requests that Rock castle use Table 2.2d, UDSA-SCS TR-55, sagebrush with grass understory, good conditions, to derive the curve numbers for the pre-mine conditions. Post-mine curve numbers are appropriately described by either the herbaceous cover type or the dryland pasture or range values in good condition from Tables 2-2d or 2-2c. Good conditions were utilized as the tables use cover values derived from litter, grasses, forties and brush and Mr. Croft's sampling shows that all the pits and the reference area have cover exceeding 80~. b. The pre-mine slope length of 150' seems short. The Division would accept 250'. c. The Division apparently utilizes Table 5.5c on CP factors differently from ACZ. The canopy cover column should reflect the living cover (herbaceous and woody) and the cover that contacts the surface column reflects all cover (herbaceous, woody, litter and rock) . Attachment 1 -Pit 5 Drainage Remediation Plan 8. This plan calls for the mixing of undisturbed and reclaimed area drainage. This is acceptable if the drainage structures are sized to handle the runoff from these areas. Please ensure that your mapping includes the entire drainage above Pit 5 and documents the entire extent of the disturbed area (pit and stockpile areas). In addition, re-evaluate the acreages noted on Figure 1 of Attachment 2. Acreages shown for the Pit 5 ditches are vastly underestimated. 9. The Division is unable to accept the general concept behind the Pit 5 Drainage Remediation Plan until we have a certified post-mining topography map. The Division is very concerned about the steep slopes along the north perimeter ditch and west of the access road and on the west edge of the disturbed area. It is the Division's preference that Rockcastle armor drainageways through the steep slopes on the north and south central portions of the pit perimeter.