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i~ <br />' This collection and pump back system consists of an interceptor trench and french drain <br />approximately 72 feet in length and 4 feet in width and depth. The trench installation acts to <br />' intercept and convey the observed seepage water, as well as other ground water flow to a <br />constructed collection sump at the downgradient end of the trench. Water collected and <br />conveyed to the collection sump is pumped back to the West Pit for infiltration back into the <br />pit. Permanent electrical service to the collection sump pump back equipment has been <br />' installed to allow the continual pump back of the seepage water to the West Pit. The water <br />is currently pumped back at a rate of approximately 400 gallons per minute ('Figure 10). <br />' The pumped water was initially discharged on the surface of the reclaimed West Pit. <br />However, problems with slow infiltration and freezing have necessitated some changes to the <br />' discharge. An infiltration trench approximately 15 feet deep has been cotstructed along a <br />north south plane extending from inside the southern perimeter of the West Pit highwal] to the <br />' toe of the exposed northern pit highwall. The infiltration trench will be completed with a <br />french drain bedding of 6" ADS perforated corrugated pipeline to allow delivery and <br />' infiltration of the pump back water along the entire length of the infiltration trench. A second <br />pipeline will be installed in the trench to infiltrate water from an interceptor we10, if necessary. <br />' Winterization of the infiltration pipeline will be completed by backfilling the trench with the <br />excavated fill material extracted during construction. The system location is shown in Figure <br />10. <br />To prevent discharge of this seep water through the West Pit BMP established for stormwater <br />' runoff, particularly before the infiltration trench was constructed, the BMP has been <br />temporarily sealed to prevent discharge. BMRI is currently evaluating the feasibility of <br />' directing the ponded water from the stotmwater runoff and early pumping efforts to the new <br />infiltration trench system. Once ponding has been eliminated and the trench is fully <br />' operational, then the BMP will be re-established <br />' Operation of these facilities will be conducted to maintain collection and removal of the <br />seepage water throughout the proposed characterization, evaluation and implemeptation phases <br />' of a long-term response action. <br /> <br /> 16 <br />' <br /> <br />