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IMPOUNDMENT DOCUMENTATION FOR EXISTING THICKENER OVERFLOW SUMP Background The Thickener Overflow Sump (Tlricl~ner Sump), utilized in conjunction with ongoing Coal Preparation Plant water handling operations, has existed for years and was not previously identified or considered as an "impoundment° under the regulatory definition. As a restilc of changes in regulatory interpretation, however, the CDMG has determined that this existing wazer body falls under the broad definition of "impoundments° and should be identified and regulated as such Because a is an existing temporary water storage facility and was not specifically designed or constnrcted as an impoundment, the applicable regtrimmerrts of Rule 4.05.9 are addressed in this context by the following description and the referenced existing configuration drawing: A*+Pa 1 Thickener Swtr~ Design~}C teration Maintenance Inspection. and Reclamation The Thickener Sump was originally construtted as a temporary storage basin to contain the contests of the Preparation Plant Thickener Tank (approximately 15,000 gaL) in either an emergency situation, or for un-planned maintenance, where the Thickener Tank might have to be drained. The sump is immediately adjacent to and to the north of the existing Thickener Tank, as shown on Map 24, Surface Facilities, and by Figure Ex8W-1. The Thickener Sump is a taally incised excavazion, with no embankmem, varying in depth from approximately 5 to 7 feet, as shown by Figure Ex8W-1, Thickener Overflow Sump. The Thickener Sump basin is totally enclosed by undisttubed natural ground and has an estimazed maximum capacity of approximately 0.44 acre-feet (143,400 gal). Given that the existing Thickener Stung is used solely for emergency or temporary storage of a limited volume of water, it is not a designed impoundment per se, ahhotrgh an appropriate engineered water discharge system (float . pump installation) has been designed and installed The Thickener Sump is designed and used for emergency or short-term temporary storage of the contents of the Thickener Tank Water inpuu to the sump are limited to minor incident precipitation and, under overflow, emergency, or tin-planned mantenance conditions, the partial or full contenu of the Thickener Tank A partially buried overflow/drain-line from the Thickener Tank outlets to the Thickener Sump. Thickener overflows controlled by balancing system inflow and discharge rates. The Thickener Tank can be pattially or completely drained through the discharge line by opening an internal discharge valve. The surrounding Preparation Plant yard areas are graded to drain away from the Thickener Sump, and the adjacent drainage collection ditch (Ditch D-2) intercepts any drainage from the south, so any runoff contributions are negligible. The Thickener Strrtrp is managed as a storage impoundment (consistent with applicable provisions of Rule 4.05.9(2)(e)), with controIled pumping to manage impotmdment water levek. Afloat pump is used to periodically discharge water to either the Thickener Tank or the Preparation Plant make-up water irilet, in order to maintain water levek well below the crest of the sump. The pump has a capacity of 250 gpm. Power for the pump comes from a short extension cable from the Preparation Plant. Management of the Thickener Sump involves regular monitoring of water levels and periodic inspection and maintenance of pumping systems. As an impoundment, the Thickener Sump will be inspected on a monthly basis by a qualified professional using the inspection approach, criteria, and documentation forms used for MSHA impoundments, including specific inspection criteria under Rule 4.05,9(15). A copy of completed inspection forms will be provided to the CDMG, and a copy will be retained on-site and will be available for inspection and review by authorized persons. If observations during an inspection indicate that a potential hazard exists, the CDMG will be promptly notified of the potential hazard and of any appropriate emergency procedures formulated and/or implemented to protect public safety and remediaze the potential hazard. On completion of operations, it is amicipated thaz the Thickener Sump will be reclaimed, along with the Preparation Plant facilities, as described tinder Section 2.05.4(2)(c) of the PAP. Reclamation will involve bacldilling the basin area with spoils, grading to blend with surrounding areas, topsoil replacement, and revegetazion. TR 05-48 Ex8W-2 Revised -March 2005