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evacuated before any further activity is conducted by the drilling crew. After the mine is <br />evacuated, drilling and reaming shall be completed to the casing depth. The bottom of the bore <br />hole will be sealed with grout to a point that recirculation is reestablished. After the drill hole is <br />sealed, the mine shall go back to operation. Casing installation activities can then be conducted <br />to the depth of the sealed hole bottom. <br />The layout of the completed borehole and thickener underflow discharge piping system will <br />develop a natural fluid P-trap between the preparation plant and the point of discharge into the <br />borehole into the mine, thus preventing the underground atmosphere from entering the <br />preparation plants should pumping cease for any reason. The preparation plant is approximately <br />56' above the lowest point in the line, and the top of the borehole casing at the point of discharge <br />is approximately 47 feet below the preparation plant. The top of the casing into the mine will be <br />fitted with an anti siphon valve to keep the flow into the mine from emptying the line when the <br />thickener underflow pump is shut off. An additional anti siphon valve will be fitted to the pipe <br />between the preparation plant and the top of the casing where the line enters the mine at a high <br />spot in the line. This device elevation inlet will be higher than the elevation of the preparation <br />plant to stop flow into the mine when pumping stops for any reason. <br />Other safety precautions to be taken during the drilling, reaming, and installation of the 8" ID <br />steel casing include: <br />1. As indicated on the attached schematic labeled Stuffing Box Well Head - Drilling and <br />Reaming Phase, a well head stuffing box with a blewy line at a right angle to the surface <br />casing and compressed air will be used to ventilate and move fresh air through and around <br />the drill hole and away from the casing while drilling. If water/drilling mud is used for <br />cutting removal, compressed air will continue to be used to avoid gas build up at the wiper <br />seal. The discharge air will be continuously monitored with a methane detector through a <br />sampling tube on the discharge end. While reaming into the sealed mine entry, the <br />compressed air intake will continue to force air out of the blewy line to avoid gas build up at <br />the wiper seal. <br />2. During the drilling and reaming processes and the welding installation of the 8" ID steel <br />casing, a qualified person shall test for methane in accordance with 30 CFR Part 75.150 or <br />77.101. <br />3. As indicated on the attached schematic labeled Manhole Phase Diagram, and during the <br />process of cutting off the casing at the surface and placing the wellhead, a vented mechanical <br />or inflatable packer will be placed inside the 8" ID casing at a location below the cut line. <br />Prior to cutting off the casing, the annulus will be grouted and the void between the casing <br />and the packer vent pipe will be monitored for methane. <br />4. As indicated on the attached schematic labeled Manhole Phase Diagram, and during the <br />placement of the culvert manhole, a ventilation fan with tubing reaching within V of the <br />bottom of manhole will be used to prevent the build up of methane and low oxygen <br />conditions. <br />5. If any of the mentioned safety features fail during casing or manhole installation, the activity <br />will immediately stop until the device is repaired or the mine is evacuated. <br />APPROVED <br />L:\MSHA SUBMITTED OR APPROVED PLANS\ThickenenUnderflow6Right\MSHA Cover Letter 6 Right Borehole 10310 .doc DEC 16 2009 <br />DASH