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• <br /> EXPERIMENTAL OBSERVATIONS <br /> The first study allows conclusions to be drawn about : 1 ) <br /> distances at which horizontal stresses released by the quarry <br /> excavation increase hydraulic conductivity ( i . e . extend or open <br /> existing fractures ) and 2 ) the vibration level ( i . e . distance from a <br /> given size blast ) that would be associated with increases in <br /> conductivity . In sandstone the specific capacity was not affected <br /> until the excavation approached within 114 to 200 feet of the <br /> measuring well and/or the resultant particle velocity measured at the <br /> collar ( ground surface ) of the well was 5 . 54 to 3 . 34 inches per <br /> second . The excavation producing this stress relief and vibration was <br /> 125 feet deep at its closest approach to the well . <br /> The experiments in the second study show that fractures are <br /> extended through unfractured shale , a weak rock , some 50 to 60 blast <br /> hole diameters . Since the sandstone surrounding the quarry is <br /> stronger , this extent is a conservative estimate . If the quarry <br /> operates with 4 inch diameter blast holes , unfractured rock would not <br /> fracture beyond ( 4/ 12 ) 60 - 20 ft . <br /> IMPLICATIONS FOR THE QUARRY IN QUESTION <br /> To protect against stress relief induced increases in <br /> hydraulic conductivity , a buffer zone should be placed between the <br /> edge of the landfill and the quarry cut . The width of the buffer <br /> should be proportional to the depth of the quarry excavation . For <br /> instance the north west corner of the quarry will involve a cut of <br />