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<br />II. West Ridge Waste Disposal Area <br />The WRWDA is located south of and adjacent to the Bowie #1 mine's crushing and <br />screening fill. It straddles a small northwest-southeast trending ridge. Drainage <br />generally flows to the south and southeast. Construction began in July 1983. The total <br />disturbed area associated with the pile is about 3.5 acres. Over 2 acres comprising the <br />first outslope were completed and revegetated in 1983. About 1.5 acres were seeded <br />in 1993. Seeding took place on the second bench outslope, nearing the upper limits of <br />the pile, in 1995. The northeast end of the pile currently is in use. <br />This refuse pile's design criteria include: 2h:1v maximum outslope steepness (s 50%, <br />or 26° 34' ); 20 feet-wide benches spaced at 50-foot intervals; bench inslopes of 5% <br />and grades of 5% to the east and west collection ditches; grade of the pile's top, 5%; <br />and a total height of 100 feet. Coal refuse is to be compacted in 24-inch lifts to 90% of <br />maximum dry density. The approved depth of non-toxic, non-combustible cover soil is <br />i 4 feet. We didn't verify the depth of cover on reclaimed surfaces and other <br />verification of cover depth wasn't readily available. Surface drainage is directed to the <br />WRWDA pond at the pile's southeast end through the east and west collection ditches. <br />Inaccor~apce witb~eCtion 4 09 1f~a); W~RY!(D initial) ~v!~sn't built with an underdrain <br />because of its location on the ridge where drainages, springs or seeps were not <br />encountered. Eventually, waste disposal will expand across the drainage to the east <br />ridge, and the height the WRWDA will increase to 150 feet. <br />Concerns for the pile's stability as a result of insufficient compaction, over steepened <br />slopes and seepage led to DMG's approval of TR-7 in September 1989. That technical <br />revision essentially required reconstructing the pile to approved design criteria for <br />slope steepness, lift construction, and compaction. Finger drains._ in th_~_pjle's toe also <br />were constructed..to avoid saturaticzn. The oile's reconstruction occurred in late <br />,._-__- <br />In September 1994, technical revision TR 94-25 was approved to slightly increase the <br />width of WRWDA at its north end, increasing storage volume by about 1,000 cubic <br />yards to 131,000 cubic yards of refuse. The revision modified the surface drainage <br />system on the east side of the pile and approved construction of short underdrains on <br />the northeast and northwest ends. Construction of the east underdrain was completed <br />in September 1996. The west underdrain hasn't been built yet. <br />Runoff controls on the west side of the WRWDA convey drainage through the west <br />collection ditch to the WRWDA pond. A ditch along the outside edge of the crushing <br />and screening fill above the pile conveys drainage to a 30-inch diameter half-culvert O. <br />This ditch is shown with cross section E-E on Map 8-1. Though an exhibit illustrating <br />this cross section isn't in the mine plan, technical revision TR 91-14 approved channel <br />designs that are in volume 8. The design for this ditch calls for a top width of 2.56', a <br />depth of .85 feet, a V-shaped profile, and 1.5h:1v inside slopes. Capacity is 3.32 cubic <br />feet-per-second (cfs). A 30" diameter corrugated metal pipe (CMP) culvert, labeled N <br />6 <br />