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The total volume of circuit water and solids that could possibly arrive at Pond A, assuming no losses of water to the soil along the • way and transport of all solids to the pond, is .5 ac-ft. Calculations for Pond A presented in Table 4.3-6 indicate that the required pond volume for sediment storage and specific runoff events is /.l ac-~t. In Appendrr, 4.3-2, a professional engineer certified that Pond P. has been constructed with a volume of 9.9 ac- ft, or an excess capacity of approximately 30 0. The excess capacity of Pond A is approximate ].y 5 times greater than the volume required to hold the entire slurry system volume without impacting minimum storage needs of the pond. In addition, a 60 foot deep sump has been constructed within the mine to store slurry fluid in an emergency. The other structure to be discussed in this section is the thick- ener which was briefly mentioned in Section 4.3.3.1.3 (Coal washing Plant). NCIG is planning to use a unit which is 50 ft in diameter and 20 ft deep at the center depth. The objective here is to take the -28 mesh refuse slurry from the coal washing plant and pump it into the thickener. The thickener in turn acts as a large decant pond and allows the heavier slurry product to settle and be diverted to the center underflow pumps by use of slow moving rakes pivoting on the center drive unit. The overflow orates is pumped to a clarification circuit where additional very fine refuse, -100 mesh, is removed and the remaining water pumped back underground to be used in the hydraulic mining operation. The underflow refuse slurry from the thickener is then pumped through a buried pipeline and disposed in the underground refuse area. The thickener discharge can, however, be diverted back to the process building for further coal separation and cleaning. NCIG - Coal Ridge #1 4-44 ABC/1145/910509