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IMPOUNDMENT DOCUMENTATION FOR EXISTING AREA 1 PIT TEMPORARY WATER STORAGE BASIN Backeround The Area 1 Pit Temporary Water Storage Basin (Area 1 Basin), utilized in conjunction with ongoing mine 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 CDRMS 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 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: Area 1 Temporary Water Storase Basin Design, Operation, Maintenance, Inspection, and Reclamation The Area 1 Basin is a remnant surface mine pit adjacent to the Run-of--Mine Coal Stockpile, as shown on Map 24, Surface Facilities, and by Figure Ex8V-1. The pit was mined as part of the former Energy No. 1 mine operations. Given that concurrent surface mining and reclamation operations for the Energy No. 1 Mine ceased in 1980, this pit azea has been in-place for approximately 25 years. The remnant pit area is a totally incised excavation varying in depth from approximately 40 to 50 feet, as shown by Figure Ex8V-1, Area 1 Pit Water Storage Basin. The pit area is enclosed by undisturbed natural ground on the north and west sides and backfilled surface mine spoils on the south and east sides and has an estimated maximum water storage capacity of approximately 126 acre-feet. Given that the existing mine excavation is being used for temporary water storage, it is not a designed impoundment per se, although an appropriate engineered water discharge system (fixed pumping station) has been designed and installed. The Area 1 Basin is used for temporary storage of excess mine water, as part of the closed-loop mine dewatering and recycle system. Water inputs to the pit are limited to minor spoil spring dischazge from the adjacent reclaimed surface mine spoils, minor incident precipitation, and excess dewatering flows from the mine dewatering systems. The discharge pipe to the Area 1 Basin is located neaz the northeast comer of the pit azea. While an 24-inch culvert outlet at the low point on the crest of the pit allows for minor discharge flow through the overflow channel (Site 7, design capacity of 0.8 cfs) to Pond D if the water reaches this level, the temporary storage basin is managed as a storage impoundment (consistent with applicable provisions of Rule 4.05.9(2)(e)), with controlled pumping to keep water levels below the discharge pipe. A fixed pumping station has been established on the northwest edge of the basin azea to reclaim water for mine use and to control water level. The pump station consists of several cantilevered steel beams extending over the edge of the basin, with a platform, gantry, walkway, and safety rails For access. A submersible pump, along with associated support and electrical cable, and discharge hoses and piping, is suspended from the pump station gantry within the basin. A winch on the pump station platform allows adjustment of the support cable to set the pump at the desired elevation. The pump has a capacity of 250 gpm. Power for the pump comes from a separate transformer and short (350') distribution line. With initiation of operations for Washplant II, a second pump was installed to provide make- up water for the Washplant. Pump controls were installed at the existing pump platform. The Area 1 Basin pumping installation discharges to a de-sander located at an old well site, and then to either or both of the coal washplants (Washplants I and II), to the mine water recycling system, or directly to Pond D for discharge to Foidel Creek. TCC has also obtained approval (6/26/02) from the CDPHE to discharge from the Area 1 Basin directly to Foidel Creek, contingent on constmction of a new outfall (Outfall 020). The proposed new outfall has not been constructed at this time. Management of the Area 1 Basin involves regular monitoring of water levels, inspection and maintenance of pumping systems, and reduction of water levels prior to spring dischazge to provide additional water storage capacity for any minor increases in subsequent spoil spring dischazge. As an impoundment, the Area I Basin wi[I be inspected on a monthly basis by a qualified professional using the inspection approach, criteria, and documentation forms used for MSIfA impoundments, TR07-59 Ex8V-1 02/27/07