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COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division <br /> Amendment No. 2 Rationale - Page 4. Permit Number CO-0000396 , <br /> V. DISCUSSION OF AMENDMENT: (Continued) <br /> Present Production Status: (Cont. ) needed for treatment until a later <br /> time when the mine resumes production and operation. At this later <br /> time, additional personnel will probably also be hired for operations at <br /> the mine and the WWTP. <br /> Underground Sizing Screen: Mid-Continent intends to install a grit <br /> screen, to be located underground in the tunnel, to separate and remove <br /> coarse solids prior to the flow leaving the tunnel. The permittee <br /> estimates that the screen will remove approximately 1/4 to 1/3 of the <br /> solids from the flow. These solids will be carried or conveyed to the <br /> raw coal stockpile. The addition of -the grit screen will reduce the <br /> volume of solids in the flow which reports either to the 016 ponds or to <br /> the WWTP. <br /> New Water Treatment Plant System: Mine drainage, on leaving the mine, <br /> will flow to either the 016 ponds or to the new wastewater treatment <br /> facility in the Preparation Plant via a valve box. A 6000 foot long <br /> polyethylene pipe will carry water from the valve box to the preparation <br /> plant. The water gravity will flow through the pipe and into the <br /> plant. The mine water will flow from the pipe into a recycle sump. The <br /> variable flow of the mine drainage will be leveled out in the recycle <br /> sump, which consists of a tank and pump, to provide a constant flow of <br /> approximately 600 gpm to the hydroclone inlet. Underflow from the <br /> recycle sump will go to a 36-inch diameter hydroclone system, which <br /> segregates middlings coal solids. The underflow from the recycle <br /> sump/hydroclone, containing middling solids, will go into the coal <br /> preparation plant cycle (or, as an alternative, underflow goes to the <br /> 001 ponds). Overflow from the recycle sump/hydroclone, containing very <br /> fine (less than 200 mesh) solids will proceed to flocculation, then to <br /> "finishing" (i.e. settling of fine solids) in the sediment pond at <br /> outfall 020 (or, as an alternative, the 001 ponds will be used for <br /> "finishing") . Flocculant will be added to the flow in a dosage of 10 <br /> ppm or less, metered automatically according to flow. MRL-100 (guar <br /> gum) will be used as the flocculant. The flocculant will be stored in a <br /> 1000 gallon tank, then introduced to the mine water at the static mixer, <br /> as flocculant and water enter the 2000 gallon dynamic mixing rank. <br /> The flocculated water gravity will flow from the tank to the 020 pond <br /> through a pipe, which will extend from an upper story of the wash plant, <br /> to the pond. The pond will be used as a "finishing" or clarification <br /> pond from the less than 200 mesh solids. The 020 pond is presently <br /> under-utilized. It was originally designed to provide sediment control <br /> for the underground storage bunkers, on which construction has been <br /> delayed. On proceeding with construction and installation of the <br /> storage bunkers, Mid-Continent will review the adequacy of the pond for <br /> sediment control, given its usage as a finishing pond. If necessary, at <br /> that time, Mid-Continent will provide additional sediment control <br /> facilities for run-off from the storage bunkers. The 020 pond has a <br /> volume of 39,830 cubic feet. Retention time, assuming an inflow of 1000 <br />