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.=.. <br />BOREHOLE ANALYSIS (con't) <br />FUTURE VENTILATION NEEDS <br />The panels in 4-Dip are on a 6% pitch between the top and <br />bottom entries. Therefore, the top return should be designed <br />to carry most of the methane. In 6-East, without a borehole, <br />the top return must have the capacity to carry 700cfm of <br />methane. In 6-East, the top return can be designated a gob <br />bleeder split and without a borehole, this return will need <br />the capacity of 75,000cfm at the mouth of the section and 55,000 <br />cfm outby the cave line. With a borehole, the top return will <br />need 55,000cfm at the mouth of the section and 40,000cfm outby <br />the cave line. <br />In the second quarter of 1986, 4-Dip/6-East is forecast to <br />be on retreat at the same time as 3-Dip is being sealed. After <br />3-Dip is sealed, the computer predicts 260,000cfm of air available <br />at the top of 4-Dip. The 3-Dip mining crew will immediately move <br />to 4-Dip/1-West after finishing 3-Dip. 1-West, towards its com- <br />pletion, will require 80,000cfm of air at the mouth of the section. <br />This leaves 150,000cfm available to 4-Dip/6-East and the bottom <br />of 4-Dip,45,000cfm of which is due to a larger fan at the Hubbard <br />Creek facility. The 6-East section will need 115,000cfm without <br />a borehole, and 95,000cfm with a borehole. With a borehole, the <br />bottom of 4-Dip should have 55,000cfm available to breach the <br />4-Dip/8 West seals, which should be sufficient. <br />COST <br />The total cost of the 6-East borehole is projected to be <br />between $125,000 and $150,000. This includes building a road, <br />moving the pump, a flame arrester, drilling the hole, and casing. <br />The total projected tonnage in 6-East is 490,000 tons. Retreat <br />mining should net 310,000 tons at approximately $.40 per ton <br />added cost for the borehole installation. <br />CONCLUSIONS <br />The advantages to a 6-East borehole are reduced air require- <br />ments and improved control over the ventilation system. A bore- <br />hole is projected to reduce the air requirement's in the section <br />by 15,000 to 30,000 cfm. Also, methane in the roof strata <br />surrounding the hole is.continuously being liberated away from <br />the face. The disadvanteages are added cost per ten of coal- <br />due to the drilling costs and access to the degasificetion <br />facility in the Winter and Spring months. <br />In conclusion, since 6-East does not have rooms planned <br />up the hill, a gob bleeder split is very desirable. With a <br />gob bleeder split and 115,000cfm of air, I feel that 6-East can <br />get by without a borehole. However, I do not feel 35,000cf° <br />air is sufficient to rehabilitate the bottom of 4-Dip, which 1~ <br />what will be available without a borehole. It would be beneficial <br />to the mine to have the bottom of 4-Dip rehabilitated promptly. <br />I, therefore, reoommend a borehole be drilled into 4-Dip/6-East. <br />2 <br />