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product from the screens 4,i11 be diverted to the coarse slurry side <br />of the ponds and r_he -2" r,roduct will continue on through the <br />circuit as crushing ti,ould not be required. <br />As stated above, the slurry hc,lding tank will be designed to retain <br />as a minimum, the entire vv Lane of solids (100 cu-yds) expected in <br />the slurry circuit at any one time. Should the slurry system <br />require emergency shut-down, the solids will be retained in the <br />slurry holding tank while the liquids will be decanted and <br />delivered to Pond A via a pipe system around the tank and a short <br />emergency overflow ditch connected to the nearest diversion ditch <br />(Figure 4.2-3) This ditcf~ will be trapezoidal in cross section, <br />2:1 sideslopes, 20 gradient, and will convey the design discharge <br />of 9 cfs at a depth of 1.1 feet and velocity of 3.7 feet/second. <br />NCIG commits to maintaining a minimum ditch depth of 2'. The <br />existing diversion ditches and culverts are sized to accommodate <br />I, maximum natural runoff rates which would exceed the maximum <br />emergency flow rate of approximately 9 CFS (Table 4.2-3). The peak <br />flow of 9000 gpm (or 9 CFS) would not be expected to last more than <br />thirty minutes, even if the entire circuit volume were lost. This <br />is unlikely since only the water in the gravity portion of the <br />circuit would be expected to flow from the mine during a shut-down. <br />The pressurized portion of tl~e circuit would contain check-valves <br />such that most of this water would be retained in the piping. <br />The worst case system failure is considered to be a pipe break <br />above the slurry holding tank where the entire system volume is <br />pumped onto the ground. In this instance, the water would be <br />directed to Pond A via the numerous diversion ditches, and the <br />solids would likely settle out along the route. The finer portion <br />of the solids could arrive at Pond A. As stated in Section <br />4.3.9.3, any solids delivered to Pond A would be removed and either <br />be returned to the coal circuit or delivered to the refuse slurry <br />line. The water would be pumped back to the water circuit. <br />. NCIG - Coal Ridqe #1 4-43 ABC/1145/910509 <br />-i~?-7 <br />