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discharge or mixing of mine water with surface drainage. Following installation of appropriate ASC's for each portion
<br />of the project disturbance, available soil materials will be bladed from any new disturbance areas and temporarily
<br />windrowed or stockpiled on the upgradient edge of these disturbance areas. For pipeline trench areas, consideration of
<br />soil horizon segregation must be balanced with the objective of limiting overall surface disturbance. In the interest of
<br />minimizing overall surface disturbance, TC proposes to not segregate and separately stockpile individual soil horizons
<br />for the pipeline trench disturbance, and submits that this approach will not significantly alter soil suitability
<br />characteristics, since the differences between the soil horizons is not significant over the areas to be affected by
<br />trenching. For the borehole drill -pad, individual soil horizons will be segregated, if present.
<br />Soil materials will be replaced following completion of pipeline installation. Reseeding of the disturbed areas will
<br />be completed during the first appropriate planting period following soil material replacement. When no longer
<br />needed to support ongoing or future mining and related operations, the thickener underflow borehole will reclaimed
<br />by removing the surface manhole structure, plugging and sealing the borehole, consistent with State Engineer
<br />requirements; cutting -off the casing below ground level, and placing a permanent marker; then regrading, replacing
<br />soil materials, and reseeding the associated disturbance areas. Pipelines will be abandoned in-place, with the ends
<br />of the pipelines cut-off and capped below grade.
<br />15LT Ventilation Shaft (TR11-77) - As a limited, temporary, surface disturbance, construction of the 15LT
<br />Ventilation Shaft will have minimal impacts on surface water hydrology, relative to runoff and sediment contributions.
<br />The short light -use road will be in a relatively flat upland area, and will be surfaced with gravel to control runoff and
<br />erosion. A designed culvert will pass any drainage from the existing natural drainage on the west side, under the light -
<br />use road. Upland drainage above the pad will be intercepted by designed diversion ditches and routed around the pad,
<br />discharging into existing short natural feeder drainages to Fish Creek. The pad will be sloped to drain to the cuttings
<br />pit, which has been sized to provide sufficient excess capacity to contain drainage flows, and the pad surface will be
<br />graveled to control runoff and erosion. Drainage from the pad outslopes will be controlled by stabilizing these areas
<br />with the temporary revegetation seed mix, and by an ASC consisting of a downslope interceptor ditch and rock -lined
<br />sediment trap. As a very limited disturbance area (approximately 2.3 acres) the road and pad disturbance areas meet the
<br />applicable criteria for a Small Area Exemption, the proposed drainage control measures should be effective in
<br />controlling runoff and sedimentation, and construction of full-scale drainage and sediment control structures is neither
<br />needed nor justified.
<br />16LT Utility Borehole (TR11-78) — The 16LT Utility Borehole installation has been designed and will be constructed
<br />to minimize and control runoff and sediment. The associated light -use road is located primarily in upland areas. Where
<br />it traverses minor ephemeral drainages, designed culverts will be installed to pass the drainage under the road. In
<br />upland areas, near the top of the sub -watershed, road drainage will be limited, however several culverts will be installed
<br />to pass minor drainage under the road to assure road stability. Both the light -use road and the borehole pad will be
<br />surfaced with gravel to control runoff and minimize sediment mobilization and transport. The proposed pad location
<br />is on the side of a small knoll, so upgradient drainage will be limited. The limited amount of drainage from
<br />upgradient areas will be intercepted and routed around the borehole pad by a small designed upgradient diversion
<br />ditch on the west and north sides of the pad. Drainage from the pad will be controlled under a Small -Area
<br />Exemption by gravel surfacing on the pad surface, temporary revegetation seeding of pad cut/fill slopes, and by an
<br />interceptor ditch along the south and east sides of the pad, (size the same as the diversion ditch, although the
<br />drainage area is significantly smaller), draining through a rock sediment basin. As a very limited disturbance area
<br />(approximately 2.2 acres) the pad disturbance area meets the applicable criteria for a Small Area Exemption, the
<br />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 Pipefines (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 />TR18-91 2.05-84.10 08/20/18
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