2013-10-17_PERMIT FILE - C1982056A (4)

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proposes to not segregate and separately stockpile individual soil horizons for the pipeline trench disturbance, and submits that this approach will not significantly alter soil suitability characteristics, since the differences between the soil horizons is not significant over the areas to be affected by trenching. For the borehole drill -pad, individual soil • horizons will be segregated, if present. Soil materials will be replaced following completion of pipeline installation. Reseeding of the disturbed areas will be completed during the first appropriate planting period following soil material replacement. When no longer needed to support ongoing or future mining and related operations, the thickener underflow borehole will reclaimed by removing the surface manhole structure, plugging and sealing the borehole, consistent with State Engineer requirements; cutting -off the casing below ground level, and placing a permanent marker; then regrading, replacing soil materials, and reseeding the associated disturbance areas. Pipelines will be abandoned in- place, with the ends of the pipelines cut -off and capped below grade. 15LT Ventilation Shaft (TR11 -77) - As a limited, temporary, surface disturbance, construction of the 15LT Ventilation Shaft will have minimal impacts on surface water hydrology, relative to runoff and sediment contributions. The short light -use road will be in a relatively flat upland area, and will be surfaced with gravel to control runoff and erosion. A designed culvert will pass any drainage from the existing natural drainage on the west side, under the light - use road. Upland drainage above the pad will be intercepted by designed diversion ditches and routed around the pad, discharging into existing short natural feeder drainages to Fish Creek. The pad will be sloped to drain to the cuttings pit, which has been sized to provide sufficient excess capacity to contain drainage flows, and the pad surface will be graveled to control runoff and erosion. Drainage from the pad outslopes will be controlled by stabilizing these areas with the temporary revegetation seed mix, and by an ASC consisting of a downslope interceptor ditch and rock -lined sediment trap. As a very limited disturbance area (approximately 2.3 acres) the road and pad 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. 16LT Utility Borehole (TRII -78) — The 16LT Utility Borehole installation has been designed and will be constructed •to minimize and control runoff and sediment. The associated light -use road is located primarily in upland areas. Where it traverses minor ephemeral drainages, designed culverts will be installed to pass the drainage under the road. In 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. Field Geotechnical Investillations — TCC occasionally conducts field geotechnical investigations prior to, and as the basis for, design and construction of engineered structures. Geotechnical investigations typically involve shallow soil borings (up to 30 feet) using a hollow -stem auger, and/or excavation of shallow (up to 15 feet) test pits. For both soils borings and test pits, surface disturbance is minimal (no more than 10 x 10 feet for boreholes, and 10 x 15 feet for test pits) and both disturbance and subsequent stabilization occur within a timeframe of less than one day for each site (typically test pit excavation/soils boring, and backfilling and leveling of the resultant small area /auger -hole, occurs in a continuous sequence within the course of less than two hours for each location). The geotechnical investigation activities do not involve the use of water and are conducted under dry conditions, so the potential for related hydrologic impacts is negligible. • All geotechnical disturbance is reseeded by broadcast seeding within 6- months of disturbance, although natural revegetation typically occurs much sooner due to the limited timeframe and extent of the associated disturbance. Occasionally perforated PVC pipe may be inserted in a completed borehole, and the remainder of the hole TR11 -78 2.05 -84.8 09/15/11