Laserfiche WebLink
Mountain Coal Company Exhibit 69 <br />West Elk Mine Mine Dewatering & Treatment Facilities <br />a <br />r~ <br />L <br />There will be two sludge drying lagoons each measuring 70 feet wide, 280 feet long, <br />and 6 feet deep. The lagoons will be lined with concrete underlain by a <br />geomembrane material to ensure water tightness. A concrete decant structure will <br />be provided in each lagoon. <br />Finishing Pond <br />The treated water from the water treatment building will be discharged via an <br />underground pipe to the Finishing Pond, which has been designed as a detention <br />pond (i.e. the outlet is a fixed weir). The pond will also receive treated storm water <br />via an underground pipe from the Stormwater Runoff Pond, which is adjacent to the <br />treatment building. The Finishing Pond will be lined with geomembrane material to <br />ensure water tightness. The pond dimensions will be 60 feet wide, 120 feet long, <br />and 10 feet deep. A six-foot high chain link fence topped with three-strand barbed <br />wire will be provided to restrict unauthorized entry and wildlife access. The <br />estimated length offence is 450 feet. <br />The pond will have an non-gated outlet structure that discharges to the west fork of <br />the Sylvester Gulch immediately to the north of the pond. A 12-inch fused HDPE <br />pipe installed on the ground surface will be used as the discharge pipe. At Sylvester <br />• Gulch, the pipe will discharge approximately two feet above the creek flow line, and <br />will be protected by approximately five cubic yards of 12-inch riprap. Additional <br />erosion protection will be provided in the outlet structure by using an energy <br />dissipator. The outlet structure will be constructed of concrete as shown in the <br />designs included in Exhibit 66. <br />Stormwater Control <br />Site drainage will be consistent with drainage designs provided in PR07 and MR212, <br />and as required by Rule 4.05.6. The only disturbed area requiring Stormwater runoff <br />control for the dewatering and treatment facilities is the pad on which the <br />Dewatering Pump Station and Treatment Building will be located. All other <br />facilities (i. e. ponds) will contain the precipitation falling on them, and road drainage <br />will be captured by existing ditches DSLY-8A and 8B as shown on Map 54B. <br />Calculations are included in Exhibit 66. <br />An earthen Stormwater Runoff Pond will be provided immediately adjacent to the <br />pad to be used for Stormwater only. The pond is designed in accordance with Rule <br />4.05.6 to provide both sediment storage and Stormwater storage. The bottom two <br />feet will be reserved for sediment storage. The principal spillway will consist of a <br />valved 6-inch outlet pipe and will be installed so that the invert elevation is at the top <br />of the sediment profile. The Stormwater Pond has been conservatively sized to <br />• completely hold 100% of the precipitation and sediment from a 25-year, 24-hour <br />4 Yav. 1997 ~fR232 <br />