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At each of these locations, a drill -pad and required drainage structures were constructed. Buried thickener
<br />underflow pipelines have been or will be installed between the existing washplant facilities and the thickener
<br />underflow boreholes. The locations of both the thickener underfloor boreholes and the associated pipelines are shown
<br />on the Surface Facilities and Freshwater Systems Map, Map 24 (1/4). Design information for the thickener underflow
<br />boreholes and pipelines is provided in Exhibits 49K and 49S.
<br />Installation of the thickener underflow boreholes involves placement of construction erosion controls (silt fence
<br />and /or straw wattles), removal and windrowing of available soil materials from pad areas and the road margins,
<br />grading to establish level drill -pads and construct or improve access roads, placement of gravel as surfacing for the
<br />light -use road, excavation of temporary cuttings pits on the drill -pads, drilling and casing of the boreholes, and
<br />installation of protective access manholes. On completion of drilling and casing operations, the cuttings pits are
<br />allowed to dry-out, material excavated from the pits is replaced and graded, and the pad surface is graveled to control
<br />erosion and sediment and provide an all- weather operating surface. The completed thickener underflow borehole
<br />installations include an access road, a soil material stockpile (pad and road); the drill -pad (I MN — 25 x 180 feet, 6RT -
<br />70 x 70 feet, 7RT — 100 x 75 feet, 2MN — 75 x 75 feet); the 6- to 12 -inch cased boreholes, 16 -inch cemented surface
<br />casings, and covered 8 -foot diameter CMP culvert manholes with lightening protection.
<br />With timing and weather constraints, portions of the pipeline may be temporarily installed on the surface, to be
<br />buried when ground conditions are more favorable. Pipeline installation will involve removal and windrowing of
<br />soil materials from the pipeline construction corridor (maximum - 40 -foot wide); trenching in most areas;
<br />placement of suitable bedding materials; placement, connection, and pressure testing of the pipelines; backfilling
<br />and compaction of suitable fill materials around and over the pipelines; backfilling and compaction of the trench;
<br />regrading; replacement of soil materials; and revegetation of all disturbed areas. Where the pipelines pass under
<br />RCR27, the Twentymile Mine railroad spur, and Foidel Creek, the pipeline trench was expanded to provide room
<br />for horizontal boring equipment, and the pipelines were trenched or bored under these features. Because pipeline
<br />placement and construction of portions of the 6RT and 7RT pads necessarily involved activities within the Foidel
<br />Creek buffer zone, TC is requesting a temporary variance for pipeline construction and a longer -term variance for
<br />the limited pad areas from the regulatory requirements for operations within a buffer zone. The pipelines are a
<br />double HDPE pipe system in critical areas, with a 6 to 8 -inch carrier pipe inside a larger (maximum size - 10 -inch
<br />diameter) containment pipe, buried approximately 5 -feet deep. The 1MN pipeline extends approximately 1,800
<br />feet, with the 6RT pipeline extending approximately 8,000 feet and continuing another 1,600 feet to 7RT. The
<br />6RT /7RT pipeline is immediately adjacent to the 2MN Borehole, so only a short connecting pipe was necessary
<br />Electronic moisture sensors, along with pump controls, and shut -off valves provide for timely detection, shut -off, and
<br />isolation of the pipeline in the event of pipeline leakage. Access /inspection manholes and pipe -tees for the moisture
<br />detection system are located at key points along the pipeline routes.
<br />When the new Washplant and Thickener were installed, a new Thickener Overflow Sump was constructed to
<br />contain minor amounts of washdown water and to serve as a temporary catch basin for the contents of the
<br />Thickener, if required for maintenance or under upset conditions. The Thickener Overflow Sump is located
<br />between the Refuse Conveyor and Sedimentation Pond D. The Thickener Sump is partially incised, incorporates a
<br />compacted clay liner to minimize seepage, and is sized to fully contain the contents of the Washplant 1I Thickener
<br />(150,000 gallons) plus minor amounts of washdown water and incident precipitation for the design event.
<br />Impoundment design, operation, and maintenance information for the Thickener is provided in Exhibit 8X. Given
<br />that the potential for both the Washplant I and Washplant II Thickeners to experience an upset or require
<br />maintenance at the same time is negligible, with completion of the Washplant 11 Thickener Overflow Sump, the
<br />Washplant I Thickener Overflow Sump was decommissioned, filled -in and replaced by a discharge pipe from the
<br />Washplant I Thickener to the new Washplant I1 Thickener Overflow Sump. As an incised and closed basin (ie: no
<br />outlet) the only potential inputs to the Sump are thickener overflow, washdown water, or minor incident
<br />precipitation, which are subsequently pumped back into the system by a portable floating pump installation. The 4-
<br />inch thickener overflow line has been extended to the new Thickener Overflow Sump (4,800 feet), allowing
<br />overflow from either thickener to be controlled by valves and routed to the Sump. Water level in the Sump is
<br />monitored and managed as part of the ongoing Washplant operations.
<br />Given the power and system control requirements for the Washplant, an associated Motor Control Center
<br />(MCC) /Office Building was constructed immediately adjacent to the Washplant. The MCC /Office Building houses
<br />electrical, control, and monitoring equipment for the Washplant and includes office space. The building consists of
<br />MR l 3 -273 2.05 -32.4 12/06/1 3
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