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proposed drainage control measures should be effective in controlling runoff and sedimentation, and construction of <br />full-scale drainage and sediment control structures is neither needed nor justified. <br />5MN Borehole and Pipelines (MR14-283, MR15-288) — Given the limited disturbance areas, the location of the road <br />and pad on top of a minor ridgeline, and the very temporary nature of the pipeline surface disturbance, the 5MN <br />Borehole pad, associated road, and pipelines will have minimal impact relative to runoff and sediment contributions. <br />Upgradient drainage will be limited, and the road will not cross any natural drainages so no culverts will be required. <br />Site drainage will be effectively controlled under a Small Area Exemption by diverting any limited upgradient drainage <br />around the pad area with a small upgradient interceptor ditch, gravel surfacing on both the access road and pad areas, <br />and temporary revegetation of any cut/fill areas. The interceptor ditch will drain through a rock -lined sediment trap to <br />the adjacent drainage to the east. As a very limited disturbance area (approximately 4.0 acres for the pad and road, of <br />which 3.1 acres is road, and 4.6 acres for the temporary pipeline disturbance) the disturbance areas meet the applicable <br />criteria for a Small Area Exemption, the proposed drainage control measures should be effective in controlling runoff <br />and sedimentation, and construction of full-scale drainage and sediment control structures is neither needed nor <br />justified. <br />10 -East Emergency Air Borehole (MR15-289) — The existing access road, temporary site access, and proposed pad <br />are located on adjacent minor ridgelines, and will have minimal impact relative to runoff and sediment contributions. <br />Upgradient drainage will be limited, and the road will not cross any natural drainages so no culverts will be required. <br />Site drainage will be effectively controlled under a Small Area Exemption by diverting any limited upgradient drainage <br />around the pad area with a small upgradient interceptor ditch and temporary revegetation of the pad surface and <br />associated cut/fill areas. The interceptor ditch will drain through a rock -lined sediment trap to the adjacent drainage to <br />the west. As a very limited disturbance area (approximately 1.5 acres for the pad disturbance) the disturbance area <br />meets the applicable criteria for a Small Area Exemption, the proposed drainage control measures should be effective in <br />controlling runoff and sedunentation, and construction of full-scale drainage and sediment control structures is neither <br />needed nor justified. <br />13 -Left Outby Utility Borehole (MR15-291) — Given the limited disturbance areas, the location of the road and pad <br />on a low -gradient sidehill, and the very temporary nature of the planned disturbance, the 13LT Outby Utility Borehole <br />pad, and associated road will have minimal impact relative to runoff and sediment contributions. The limited amount <br />of drainage from upgradient areas will be intercepted and routed around the borehole pad by a small upgradient <br />diversion ditch on the southwest and northwest sides of the pad. The existing ranch road crosses a small ephemeral <br />drainage, and the existing culvert will remain in-place. The culvert installation will be evaluated relative to <br />condition and cover to carry the anticipated truck traffic, the culvert will be replaced or extended as necessary, and <br />adequate cover will be placed to carry the anticipated loads, without crushing the culvert. Drainage from the <br />borehole pad area will be controlled under a Small -Area Exemption, with gravel surfacing on the pad and road to <br />control runoff and sediment and placement of rigid sediment filter material on the northeast side of the pad area. <br />The upgradient diversion ditches will drain through rock sediment basins to the undisturbed adjacent lands, and pad <br />cut/fill areas will be stabilized with temporary revegetation seeding. As a very limited disturbance area <br />(approximately 1.0 acres for the pad and road, of which 2.4 acres is road) the disturbance areas meet the applicable <br />criteria for a Small Area Exemption, the proposed drainage control measures should be effective in controlling runoff <br />and sedimentation, and construction of full-scale drainage and sediment control structures is neither needed nor <br />justified. <br />9 -East Utility Borehole Installation (MR16-296) — The 9 -East Utility Borehole Installation will involve limited <br />surface disturbance for the required pad and light -use road, and will remain in-place for a limited time (estimated <br />life of 3 -years). With limited run-on from the small upgradient drainage area, which will be conveyed under the <br />road through a series of culverts or diverted around the pad by a perimeter ditch with rock -lined sediment traps, and <br />a limited disturbance area, site drainage control will be addressed through a Small Area Exemption. Runoff and <br />sediment from the pad and road will be effectively controlled through the use of gravel surfacing, revegetation of <br />cut/fill areas, and downgradient sediment control for the soil stockpiles. With a limited disturbance area <br />(approximately 2.1 acres for the pad and 1.6 acres for the road) the disturbance areas meet the applicable criteria for a <br />Small Area Exemption, the proposed drainage control measures should be effective in controlling runoff and <br />sedimentation, and construction of full-scale drainage and sediment control structures is neither needed nor justified. <br />Field Geotechnical Investigations — TC occasionally conducts field geotechnical investigations prior to, and as the <br />basis for, design and construction of engineered structures. Geotechnical investigations typically involve shallow soil <br />TR16-86 2.05-84.10 11/21/16 <br />