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Roadway Drainage to RSN Dip Section; Page 13-1-62 AREA PEABODY DMG 111 0.13 0.20 121 0.15 0.21 221 4.94 7.83 231 0.32 0.47 c. The roadway drainage down Haul Road 5 and past CBA 1 on Haul Road 4 depicted on page 13-1-58 (D111) does not include the runoff from the adjacent slope south of Haul Road 5. Powderhorn only modeled the drainage for the north side of the Haul Road. Please revise the model to include the ditch south of Haul Road 5. d. The North Decline road ditch and culvert designs begin midway on the road as depicted on drawing 13-1-3. Is there currently a culvert or dip in place which would divert the upland flow into the permanent drainage ditch not noted on the maps? If not, it would appear that provision to direct the runoff into the permanent channel should be made, and the map should be amended accordingly. e. It appears that the North Decline culvert leading to Pond 7 (122) only takes into account the acreage associated with watershed 121 and not the undisturbed watershed above culvert 122. Please revise the SEDCAD+ model to take the undisturbed drainage area into account. According to the book titled, Design Hydrology and Sedimentology for Small Catchments by C.T. Haan, G.J. Barfield and J.C. Hayes, it is stated that a critical headwater height equal to 1.5 times the culvert height is reasonable for the entrance .of an ordinary culvert. For two of the roadway calculation, Powderhorn used a headwater height larger than what is normally used. On page 13-1-74, culvert 212 (culvert north of Pile) a headwater height of 4' was used for an 18" culvert. On page 13-1-92, culvert 211, Powderhorn used a headwater height of 1.5' for a 6" culvert. Please elaborate on the conditions that would allow for a greater headwater height for these culverts, or revise the SEDCAD+ model accordingly. 113. Amended air emission permits requested in this item still need to be submitted. 114. See enclosed letter dated March 14, 1997, from the Division of Wildlife. We will contact you to arrange for a site visit to discuss the rock placement issue with appropriate DOW representatives. 116. Requested statement from power companies documenting that power lines potentially subject to subsidence damage could be repaired without disruption of service is still needed. If the information is not provided prior to decision issuance, it will be necessary to stipulate