|
erosion and sediment and provide an all-weather operating surface. The completed thickener underflow borehole
<br />installations include light -use road access, one or more soil material stockpiles (pad and road); the drill -pad (I MN —
<br />25 x 180 feet, 6RT- 70 x 70 feet, 7RT — 100 x 75 feet, 2MN — 75 x 75 feet, 2SW — 250 x 170 feet max, 1 SW 175 x
<br />175 feet max, 12 -Left — 175 x 175 feet max, Sandstone Sub — 75 x 75 feet); the 6- to 12 -inch cased boreholes, 16 to
<br />18 -inch cemented surface casings, and covered 8 -foot diameter CMP culvert manholes with lightning protection. The
<br />Sandstone Sub Borehole, because it will be completed on the existing substation pad, will not require soil handling, an
<br />access road, pad construction, or surface casing or a manhole, and drainage will be contained on the pad by a
<br />constructed berm.
<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, Foidel Creek, and Fish Creek, the pipeline trench will be expanded to
<br />provide room for horizontal boring or jacking equipment, and the pipelines will be trenched, bored, or jacked under
<br />these features. Because pipeline placement and construction of portions of the 6RT, 7RT, 1MN, 2MN, 12 -Left and
<br />SWMD pads will necessarily involve activities within the Foidel Creek or Fish Creek buffer zones, TC is
<br />requesting a temporary variance for pipeline construction and a longer-term variance for the limited pad areas from
<br />the regulatory requirements for operations within a buffer zone. The pipelines will be a double HDPE pipe system
<br />in critical areas (note that entire 6RT, 7RT, 2MN, 12 left, and SWMD pipelines will be double -pipe systems), with
<br />a 6 to 8- inch carrier pipe inside a larger (maximum size - 12 -inch diameter) containment pipe, buried
<br />approximately 5 -feet deep. The 1MN pipeline will extend approximately 1,800 feet, with the 6RT pipeline
<br />extending approximately 8,000 feet, and continuing another 1,600 feet to 7RT. The 6RT/7RT pipeline is
<br />immediately adjacent to the 2MN Borehole, so only a short connecting pipe was necessary. The SWMD pipeline
<br />will extend approximately 6,700 feet from the 1MN TUF pipeline to the 2SW SWMD Borehole and will fall within
<br />the previous disturbance areas for the Haulroad C corridor and the 18 -Left Mine Water Transfer Pipeline.
<br />A pump boost station will be added prior to the 2SW borehole near the west entrance truck scales to provide
<br />sufficient pumping capacity to efficiently move the coal fines through the pipeline network toall of the designated
<br />locations (I SW, 2SW, and 12 Left). From the 2SW location, the pipeline will extend approximately 2,930 feet
<br />northeast to reach the 1 S borehole location. An additional pipeline (12 -Left pipeline) will tee off the pipeline
<br />running from the 2SW borehole to the 1 S borehole on the east side of RCR27. The pipeline will parallel RCR27
<br />for an additional 7,700 feetextending to the northwest, crossingunder Fish Creek, and then continuing southwest to
<br />the 12 -Left Borehole location. Limited areas of pipeline construction will fall within the Foidel Creek and Fish
<br />Creek stream buffer zones, and both general and specific BMP's will be used to prevent adverse impacts to the
<br />hydrologic balance. The Sandstone Sub pipeline will extend approximately 1,200 feet from the 1MN Borehole
<br />location. Electronic moisture sensors, along with pump controls, and shut-off valves provide for timely detection,
<br />shut-off, and isolation of the pipeline in the event of pipeline leakage. Access/inspection manholes and pipe -tees for
<br />the moisture detection system will be located at key points along the pipeline routes.
<br />During construction, and for the minor surface structures that will remain during mining, drainage and sediment control
<br />will be provided by Alternative Sediment Controls (ASC's) consisting of combined Best Management Practice (BMP)
<br />measures. As appropriate, ASC designs are included in the design exhibits for each installation. BMP's for the
<br />construction activities include (BMP's for any stream buffer zone areas include the general BMP's identified, as well as
<br />specific BMP's* as noted):
<br />• Minimizing the area of surface disturbance
<br />• Placement of stream buffer zones markers prior to disturbance in or immediately adjacent to buffer zone areas*
<br />• Scheduling of construction activities during the dry summer or early winter periods
<br />• Placement of staked straw wattles, silt fencing, or plastic silt barrio materials downgradient of all surface
<br />disturbance areas to intercept any surface runoff and trap associated suspended solids
<br />• Installation of the Foidel Creek, Fish Creek, RCR27, and railroad spur pipeline crossings as either trenched or
<br />bored/jacked pipeline crossings under Foidel Creek, Fish Creek, RCR27 and the railroad spur (if trenched, TC
<br />TR17-88 2.05-84.7 06/10/17
<br />
|