2013-12-17_PERMIT FILE - C1992081 (19)

Home Browse Search

piles have been permitted as small area exemptions by CDRMS. The following briefly describes the input and output from the small area exemption SEDCAD+ analyses. Input Summary 10 -yr, 24 -hr Precipitation 1.6 inches CN Factor 48 K Factor 0.25 CP Factor 0.075 Output Summary Topsoil Pile 1 0.0 Topsoil Pile 2 0.0 Topsoil Pile 3 0.0 Substation: There is an electrical substation located in the northwest corner of the facilities area as shown in Exhibit 12 -2, Surface Water Control Plan Map. The substation is enclosed within a 30 by 40 foot area which is graveled and fenced. Also associated with the substation is a small disturbance area outside the fence. Runoff from the substation area does not drain to the Truck Loop Pond and is controlled using sediment fence. The location of the sediment fence is shown on Exhibit 12 -2. The sediment fence is designed to safely pass the peak discharge from a 10 -yr, 24 -hr event. The design demonstration is presented in Appendix 12- 2, Small Area Exemption Demonstrations. Given the limited size of the disturbance area and the demonstration that a sediment fence provides adequate control, HGTI received CDMG approval to permit this area as a small area exemption. Office/Parking Lot/Leach Field: An office /change building, parking lot and leach field was constructed on the west side of the facilities area circa 1979 as shown on Exhibit 12 -2. In 2007, as part of MR -15, HGTI placed a temporary office trailer adjacent to the existing office /change building. The trailer was placed over a portion of the existing parking lot area, which was already permitted as a disturbed area. Consequently there was no new disturbance associated with the temporary office trailer. The total disturbance associated with the office /change building, temporary office trailer and parking lot is approximately 0.3 acres. The disturbance associated with the existing leach field (0.45 acres) has been successfully revegetated. Runoff from these areas does not drain to the Truck Loop Pond but is controlled with a sediment fence. The location of the sediment fence is shown on Exhibit 12 -2. The sediment fence is designed to safely pass the peak discharge from a 10 -year, 24- hour event. The design demonstration is presented in Appendix 12 -2, Small Area Exemption Demonstrations. Given the limited size of the disturbance area and the demonstration that a sediment fence provides adequate control, HGTI requested, and received CDRMS approval to permit this area as a small area exemption. Railroad Loon: The railroad loop was constructed in the 1979/1980 period. All disturbance associated with the construction of the loop has been topsoiled and successfully revegetated with a stabilization seed mixture (identified as DHG [ Revegetated Hayden Gulch Disturbance] in Tab 10, Vegetation). Total revegetated area associated with the railroad loop is approximately 70.8 acres. The disturbance area is shown on Exhibit 12 -1. TR -10 4 Revised 02/13