2015-12-23_PERMIT FILE - C1982056 (4)

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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 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 full-scale drainage and sediment control structures is neither needed nor justified. Field Geotechnical Investigations — TC 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 backfilled with clean gravel, as a temporary piezometer installation to measure any fluctuation in water -levels. This type of piezometer installation is normally very temporary (typically used less than a month) and will not impact groundwater due to the shallow depth and use of natural cuttings as backfill. Any piezometer installations are reclaimed by either pulling the PVC pipe and placing additional fill, or plugging the PVC pipe in-place using bagged bentonite grout, then capping the installation with a minimum 1.5 -foot surface plug of natural clays or cement with a site marker. Loadout Area Drainage Modifications (MR14-284) - The drainage and sediment controls for this area were approved under an SAE, as referenced in the Permit text, however, given the configuration and type and level of activities in this area, the existing drainage and sediment controls were found to be marginally adequate. The site conditions were reviewed and evaluated, and the following changes, as shown on Figure EX49DD-F1, were implemented to modify and upgrade the site drainage controls in order to be effective under all reasonably anticipated conditions. The pad area on the north side of the rail spur was reduced in size by removing the accumulation of coally material, and regrading and reseeding part of this area, leaving only an access road along the north side of the spur. The drainage configuration of the remaining pad was modified by filling a low area and placing a berm to direct all drainage to the collection sump. The sump capacity and function were expanded by constructing a second sump in series, removing accumulated sediment from the existing sump, and rebuilding the rock perimeter filter. The control capacity of the rail spur collection ditch was increased by excavating several sediment traps in the ditch and adding additional rock check dams. As a very limited disturbance area (approximately 1.2 acres) the Loadout area disturbance 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. (5) Topsoil. A narrative explaining the method of removal and the amount to be removed and the plan for storage of topsoil, subsoil, and other material within the permit area subject to requirements of the topsoil removal MR15-291 2.05-84.10 11/11/15