2014-10-31_PERMIT FILE - C1981044A

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All major components of the system are shown on the Structures and Renewable Resources Map (Map 25). The No. 5 Mine sump is located in the lowest structural portion of the No. 5 Mine. All water encountered in the No. 5 Mine is pumped to the sump. In addition, boreholes were drilled from the No. 5 Mine to the No. 6 Mine to allow pumping of water encountered in the No. 6 Mine to the No. 5 Mine Sump. The locations of these holes were determined based on water volumes encountered. Water from the No. 5 Mine sump is pumped to the surface through two 20 -inch boreholes. The boreholes were drilled vertically from the Williams Fork River valley approximately 520 feet to the No. 5 Mine sump. It was anticipated that a chemical treatment system would be needed to treat the mine water discharge, however experience has shown that chemical treatment is not required. Presently, there is no chemical treatment system, but if significant changes in water quality were to occur, an appropriate system could be designed and installed. Due to failure of the downhole pump, the pump was replaced in 2011 with a pump of similar design and capacity. A series of three ponds have been constructed in the Williams Fork River floodplain to settle out suspended solids from the raw mine water. Each pond has a capacity of 60,000 cu -ft, which translates into a three -hour retention time per pond, at design capacity. Based on the system design, only two of the three ponds are in service at a given time. The total retention time is six hours. Operating experience and testing by Nalco indicates this to be a conservative design. A retention time of approximately twenty minutes is adequate for settling. The ponds are designed to adequately retain and settle suspended solids for a maximum inflow of 2,500 gpm. It has been estimated that the total combine pumping requirements from the No. 5 and No. 6 Mines would be 1,300 —1,800 gpm, however, to date actual required pumping volumes have been substantially less than estimated. In addition to the conservative design, internal baffles (snow fencing) installed perpendicular to the direction of flow, have been used in the past to both slow flows and lengthen the flow path through the ponds. While the baffles increase the settling efficiency of each pond by slowing the flow and increasing residence time to allow suspended solids to drop out, experience has shown that they are generally not necessary for the ponds to function as designed. Similar to the optional chemical treatment system, MCM will monitor discharge water quality, and reserves the option to utilize baffles if necessary to maintain effective treatment and control. The general flow through the system is as follows: mine water enters on the eastern end of the system, water flows in a westerly direction through the first pond (P5), water enters a pipe on the western end of pond (P5) and flows to the eastern end of the second pond (P6) (in this description, ponds P5 and P6 are the two functional ponds), water then flows in an easterly direction towards the discharge pipe. Both the inter -pond linkage and the discharge pipe are six (6) feet above the pond bottom. The manipulation of the valves on the inlet, outlets, and inter -pond linkage allow the water to be directed and discharged from any pond at any time. The general flow schematic for the pond system is presented on Figure 53, Pond Flow Schematic. The general pond system design is shown on Figure 54, Settling Ponds - Plan View. Figure 55, Pond Cross - Section A -A', and Figure 56, Pond Cross - Section B -B', are north -south and east -west pond cross - sections. The locations of these cross - sections are shown on the Drainage and Sediment Control Map (Map 26). In order to prevent water from seeping out of the ponds, they have been lined with bentonite. The bentonite was applied to the pond bottom and embankments and mixed with the surface soil layer. The heterogeneous mass of bentonite and soil was wetted and then rolled to form a good seal. The embankments are sloped at 311:1 V and should not present any operational problems. Each of the ponds has a dewatering device located in its bottom. Once a pond is filled with settled solids, it will be taken out of service and solids removed. The water that is drained from the pond will flow into a sump and then be pumped from the sump into the first functioning pond of the system. This will prevent any discharge of water containing elevated suspended solids, into the Williams Fork River. Two ramps, as shown on Map 27, provide equipment access for pond maintenance and sediment removal. A contractor will be utilized in the maintenance operations. Accumulated sediments will be hauled to the waste disposal site or placed into an approved landfill. This material may be subject to soil and overburden testing, and depending on TR14 -36 2.05 -12 Revised 09/08/14