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IMPOUNDMENT DOCUMENTATION FOR WASHPLANT I THICKENER OVERFLOW SUMP Backeround The Thickener Overflow Sump (Thickener Sump), utilized in conjunction with ongoing Coa] 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 result of changes in regulatory interpretation, however, the CDMG has determined that this existing water body falls under the broad definition of "impoundments" and should be identified and regulated as such. Because it is an existing temporary water storage facility and was not specifically designed or constructed as an impoundment, the applicable requirements of Rule 4.05.9 aze addressed in this context by the following description and the referenced existing configuration drawing: Thickener Overflow Sumo Desien, Oaeration, Maintenance, Inspection, and Reclamation The Thickener Sump was originally constmcted as a temporary storage basin to contain the contents 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 totally incised excavation, with no embankment, 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 undisturbed natural ground and has an estimated maximum capacity of approximately 0.44 acre-feet (143,400 gal). Given that the existing Thickener Sump is used solely for emergency or temporary storage of a limited volume of water, it is not a designed impoundment per se, although 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 inputs to the sump are limited to minor incident precipitation and, under overflow, emergency, or un-planned maintenance conditions, the partial or full contents of the Thickener Tank. A partially buried overflow/drain-line from the Thickener Tank outlets to the Thickener Sump. Thickener overflow is controlled by balancing system inflow and discharge rates. The Thickener Tank can be partially or completely drained through the discharge line by opening an internal discharge valve. The surrounding Preparation Plant yard azeas aze 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 mnoff contributions are negligible. The Thickener Sump is managed as a storage impoundment (consistent with applicable provisions of Rule 4.05.9(2)(e)), with controlled pumping to manage impoundment water levels. Afloat pump is used to periodically discharge water to either the Thickener Tank or the Preparation Plant make-up water inlet, in order to maintain water levels 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 remediate the potential hazard. On completion of operations, it is anticipated that the Thickener Sump will be reclaimed, along with the Preparation Plant facilities, as described under Section 2.05.4(2)(c) of the PAP. Reclamation will involve TR OS-48 Ex8W-1 Revised - Mazch 2005