2017-05-18_PERMIT FILE - C1982056A (6)

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upland areas, near the top of the sub -watershed, road drainage will be limited, however several culverts will be installed to pass minor drainage under the road to assure road stability. Both the light -use road and the borehole pad will be surfaced with gravel to control runoff and minimize sediment mobilization and transport. The proposed pad location is on the side of a small knoll, so upgradient drainage will be limited. The limited amount of drainage from upgradient areas will be intercepted and routed around the borehole pad by a small designed upgradient diversion ditch on the west and north sides of the pad. Drainage from the pad will be controlled under a Small -Area Exemption by gravel surfacing on the pad surface, temporary revegetation seeding of pad cut/fill slopes, and by an interceptor ditch along the south and east sides of the pad, (size the same as the diversion ditch, although the drainage area is significantly smaller), draining through a rock sediment basin. As a very limited disturbance area (approximately 2.2 acres) the pad disturbance area meets the applicable criteria for a Small Area Exemption, the proposed drainage control measures should be effective in controlling runoff and sedimentation, and construction of full-scale drainage and sediment control structures is neither needed nor justified. 5MN Borehole and Pipelines (MR14-283, MR15-288) — Given the limited disturbance areas, the location of the road and pad on top of a minor ridgeline, and the very temporary nature of the pipeline surface disturbance, the 51VIN Borehole pad, associated road, and pipelines will have minimal impact relative to runoff and sediment contributions. Upgradient drainage will be limited, and the road will not cross any natural drainages so no culverts will be required. Site drainage will be effectively controlled under a Small Area Exemption by diverting any limited upgradient drainage around the pad area with a small upgradient interceptor ditch, gravel surfacing on both the access road and pad areas, and temporary revegetation of any cut/fill areas. The interceptor ditch will drain through a rock -lined sediment trap to the adjacent drainage to the east. As a very limited disturbance area (approximately 4.0 acres for the pad and road, of which 3.1 acres is road, and 4.6 acres for the temporary pipeline disturbance) the disturbance areas meet the applicable criteria for a Small Area Exemption, the proposed drainage control measures should be effective in controlling runoff and sedimentation, and construction of full-scale drainage and sediment control structures is neither needed nor justified. 10 -East Emergency Air Borehole (MR15-289) — The existing access road, temporary site access, and proposed pad are located on adjacent minor ridgelines, and will have minimal impact relative to runoff and sediment contributions. Upgradient drainage will be limited, and the road will not cross any natural drainages so no culverts will be required. Site drainage will be effectively controlled under a Small Area Exemption by diverting any limited upgradient drainage around the pad area with a small upgradient interceptor ditch and temporary revegetation of the pad surface and associated cut/fill areas. The interceptor ditch will drain through a rock -lined sediment trap to the adjacent drainage to the west. As a very limited disturbance area (approximately 1.5 acres for the pad disturbance) the disturbance area meets the applicable criteria for a Small Area Exemption, the proposed drainage control measures should be effective in controlling runoff and sedimentation, and construction of full-scale drainage and sediment control structures is neither needed nor justified. 13 -Left Outby Utility Borehole (MR15-291) — Given the limited disturbance areas, the location of the road and pad on a low -gradient sidehill, and the very temporary nature of the planned disturbance, the 13LT Outby Utility Borehole pad, and associated road will have minimal impact relative to runoff and sediment contributions. The limited amount of drainage from upgradient areas will be intercepted and routed around the borehole pad by a small upgradient diversion ditch on the southwest and northwest sides of the pad. The existing ranch road crosses a small ephemeral drainage, and the existing culvert will remain in-place. The culvert installation will be evaluated relative to condition and cover to carry the anticipated truck traffic, the culvert will be replaced or extended as necessary, and adequate cover will be placed to carry the anticipated loads, without crushing the culvert. Drainage from the borehole pad area will be controlled under a Small -Area Exemption, with gravel surfacing on the pad and road to control runoff and sediment and placement of rigid sediment filter material on the northeast side of the pad area. The upgradient diversion ditches will drain through rock sediment basins to the undisturbed adjacent lands, and pad cut/fill areas will be stabilized with temporary revegetation seeding. As a very limited disturbance area (approximately 1.0 acres for the pad and road, of which 2.4 acres is road) the disturbance areas meet the applicable criteria for a Small Area Exemption, the proposed drainage control measures should be effective in controlling runoff and sedimentation, and construction of frill -scale drainage and sediment control structures is neither needed nor justified. 9 -East Utility Borehole Installation (MR16-296) — The 9 -East Utility Borehole Installation will involve limited surface disturbance for the required pad and light -use road, and will remain in-place for a limited time (estimated life of 3 -years). With limited run-on from the small upgradient drainage area, which will be conveyed under the road through a series of culverts or diverted around the pad by a perimeter ditch with rock -lined sediment traps, and TR 17-87 2.05-84.10 03/14/17