GENERAL33122 - Laserfiche WebLink

Home Browse Search

-16- that the structure would have to be designed for the 100-year, 24-hour event. The applicant's original responses to the P.A.R. stated that the ditch diverts runoff from the draw at the inlet end, around the RRCO revegetation test plot and would not be removed during reclamation. The Division, in the adequacy Zetter of January 18, 1982, requested specific information regarding construction and stabilization of the permanent diversion, and requested that the applicant clarify whether the haul road and culvert were to be maintained or removed following cessation of operations. In the responses to that adequacy letter, the applicant states, and has indicated on the Reclamation Plan Map, that the diversion around the ARCO test plot will be eliminated and the drainage will be restored to its natural pattern as a part of reclamation. All culverts will be removed and the haul road will be reclaimed. A number of concerns were noted by the Division in the January 18, 1982 letter regarding the proposed sedi~rent control system for the 8-acre sear No. 3 surface facilities area. Drainage control at the site will include a sediment pond and a system of collection ditches and culverts. The Division noted that Ditches R and B have design velocities of 7 and 9 feet per second, respectively, and suggested rock riprap protection in areas where uncon- solidated msterial is encountered. It was also requested that curved sections of Ditch R and B be protected by rock riprap and that the design depth be increased by 0.5 feet. The applicant revised the plan to comply with the Division's recommendations. A second problem noted by the Division related to sediment pond design. The Division requested an embankment cross-section and a plan view drawing of the sediment pond. The Division also requested that the emergency spillway be constructed at least 2.2 feet deep to pass the design flow and provide I foot of freeboard. The emergency spillway design was revised as requested and the design drawings were provided to the Division. R review of the sediment pond design revealed that ground water will collect in the pond, filling up a portion of the runoff storage capacity. The following stipulation is necessary: STIPULATION NO. 1 PRIOR TO SEDIMENT POND CONSTRUCTION, THE PERMITTEE WILL SUBMIT TD THE DIVISION REVISED POND DESIGNS WHICH WILL INSURE THAT RUNOFF STORAGE CAPACITY WILL NOT BE REDUCED BY GROUND WRIER DRAINING INTO THE POND AT RNY TIME DURING THE YEAR. FURTHERMORE, THE PLAN WILL INCLUDE R PROPOSAL FOR LINING THE POND, OR OTHERWISE PREVENTING THE CONTAMINATION OF NEAR SURFACE GROUND WATER AS A RESULT OF PERCOLATION THROUGH THE ALLUVIUM. The BLM pointed out that, due to the location of the proposed Bear No. 3 surface facilities on the flood plain of the North Fork, there was a potential that portions of the facilities would be inundated by flooding of the North Fork. The applicant has submitted a map indicating the water levels that would be reached at various flood stages, verifying that portions of the site, notably the sediment pond and coal stockpile, would be affected by waters of the 10-year and 50-year recurrence flood. The major portion of the facilities area would be inundated by a 100-year recurrence flood.