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The installation of the silencer will occur within the existing disturbed area. The silencer is essentially a box <br />containing baffles which will be approximately 31 feet long, 21 feet wide, and 20 feet high. The location of the <br />vent shaft and silencer is shown on Map 24. <br />NW Mains Ventilation Fan Sound Deflector/Absorber (MROS-192) <br />As part of TCC's ongoing efforts to minimize potential mine impacts on area residents, a sound deflector/absorber <br />unit will be installed on the NW Mains Ventilation Fan. The unit is designed to deflect fan exhaust, and to both <br />absorb and deflect any associated sound approximately 90° from its current discharge direction. Installation of the <br />sound deflector/absorber unit will require construction of foundations utilizing concrete piers and concrete grade <br />beams. The foundation will consist of twelve concrete piers (12-inch diameter x 15-21 feet deep), supporting two <br />curved reinforced concrete grade beams (12" wide x 2' deep x 31/64' long), with a reinforced concrete slab <br />between the grade beams. Two concrete piers will be poured on either side of the foundation to provide for side- <br />bracing of the sound deflector/absorber structure. The sound deflector/absorber unit will be a fabricated curved <br />steel structure, lined with sound absorbing material, approximately l2' wide x 20' high x 45' long (along centerline <br />of curvature). <br />Installation of the sound deflector/absorber unit will be on the existing NW Mains Ventilation Fan pad and will not <br />involve any new disturbance. The location and configuration of the unit is shown on Map 24 and Figure 31. As a <br />passive sound control device, the only required maintenance will involve periodic inspection and cleaning. When <br />the unit is no longer needed to control sound emissions from the ventilation fan, it will be removed and will either <br />be re-used elsewhere or salvaged. Foundations will be demolished and removed in conjunction with demolition <br />and restoration of the ventilation fan installation. <br />MROS-192 2.05 - 45.7 03/22/05 <br />