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effect creating a cavity at depth much larger than the boring due to side wall failure "down hole-- This could cause a sudden collapse to occur at the surface. It should be remembered that the drill rig usually exerts a large and vibratory force at the surface in the vicinity of the boring. 7. Drilling personnel must be alert to the potential for encountering subsurface hazards, particularly in older landfills where screening of disposal materials may have been less controlled. Although rare, a variety of hazardous situations have been encountered while drilling in landfills especially near military or chemical processing facilities. These potential hazards include: ♦ Unknown hazardous chemicals in drums or containers. These could include combustible or explosive, reactive, toxic or corrosive materials. 4 O Military munitions. ♦ Asbestos. ♦ Compressed gas cylinders (CDCs). ♦ Biomedical waste. ♦ Radioactive waste. 8. Periodically during the well construction, the work area should be monitored for levels of methane, HZS, vinyl chloride, benzene and/or other volatile organic chemicals. 9. If the well construction is not completed by the end of the working day, the hole shall be covered with a plate of sufficient overlap to prevent access to the hole and sufficient thickness and structural strength to support expected loads and the plate shall be weighted down to discourage removal. The edges of the plate .shall be covered with a sufficient quantity of wet dirt to prevent gas from escaping. Barricades shall be placed around the covered hole outside the range of possible cave-ins. 10. All pipes shall be capped at the end of each working day. 1 1 . An exhaust hood can be used to control venting LFG vapors while drilling to reduce personnel and environmental exposure_ This is mandatory in some locales. 1:18