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functioned adequately for four years with no observed problems, erosion, or sedimentation. • 4.3.9.3 Operations Impoundments In this section of the proposed operations by NCIG, a description of the slurry holding tank and thickener will be addressed. The slurry holding tank mentioned in Section 4.3.3.1.1 (Pumping and Sizing) is an emergency retention structure which, in the event of a processing circuit failure or shutdown, would provide the re- quired storage capacity to clear_ and store from the circuit all solids. The total slurry volume, based on a design maximum system flow rate of 9000 gpm (versus the previously proposed 8000 gpm) is about 800 yds', with a surge factor 'of 20% (Appendix 9.3-3 provides system volume calculations based on the higher flow rate). The tank capacity based on this volume will be 200 cubic yards, with an additional factor of safety. It should also be noted that the structure will be divided down the middle by a retaining wall which will be designed with a spillwa}~ to allow for overflow to either • side. All fluid entering the tank will be directed to Pond A via a series of baffles. After pan emergency situation has been corrected, any liquids sent to Pond A will be recovered by pumping back up to the hydraulic circuit during system start-up. Any coal solids which might remain in Pond A after recovery of the water would be collected and delivered to the process building for recovery and addition to the coal storage pile. The slurry holding tank will provide the following capabilities: 1) in the event the pumping and sizing facility is not operating, the run-of-mine slurry will bypass this system and be Plumed directly into the tank; 2) if the fines circuit (-28 mesh) is not functioning, the +28 mesh product: will continue to the preparation plant and the -28 mesh product pumped into the fine slurry side of the holding tanks; and 3) with the breaker shut down, the +2" NCIG - Coal Ridge #1 4-42 ABC/1145/910509 •