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meets the 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 />13 -Left Outby Utility Borehole (MR15-2911— 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 cant' 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 />borings (up to 30 feet) using a hollow -stem auger, and/or excavation of shallow (up to 15 feet) test pits. For both soils <br />borings and test pits, surface disturbance is minimal (no more than 10 x 10 feet for boreholes, and 10 x 15 feet for <br />test pits) and both disturbance and subsequent stabilization occur within a timeframe of less than one day for each <br />site (typically test pit excavation/soils boring, and backfilling and leveling of the resultant small area/auger-hole, <br />occurs in a continuous sequence within the course of less than two hours for each location). The geotechnical <br />investigation activities do not involve the use of water and are conducted under dry conditions, so the potential for <br />related hydrologic impacts is negligible. All geotechnical disturbance is reseeded by broadcast seeding within 6 - <br />months of disturbance, although natural revegetation typically occurs much sooner due to the limited timeframe and <br />extent of the associated disturbance. Occasionally perforated PVC pipe may be inserted in a completed borehole, <br />and the remainder of the hole backfilled with clean gravel, as a temporary piezometer installation to measure any <br />fluctuation in water -levels. This type of piezometer installation is normally very temporary (typically used less <br />than a month) and will not impact groundwater due to the shallow depth and use of natural cuttings as backfill. <br />Any piezometer installations are reclaimed by either pulling the PVC pipe and placing additional fill, or plugging <br />the PVC pipe in-place using bagged bentonite grout, then capping the installation with a minimum 1.5 -foot surface <br />plug of natural clays or cement with a site marker. <br />Loadout Area Drainaee Modifications (MR14-284) - The drainage and sediment controls for this area were <br />approved under an SAE, as referenced in the Permit text, however, given the configuration and type and level of <br />activities in this area, the existing drainage and sediment controls were found to be marginally adequate. The site <br />conditions were reviewed and evaluated, and the following changes, as shown on Figure EX49DD-F1, were <br />implemented to modify and upgrade the site drainage controls in order to be effective under all reasonably <br />anticipated conditions. <br />MR16-296 2.05-84.10 05/10/16 <br />