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CA ARNG Field Quality Assurance Project Plan <br /> lost circulation)change rapidly in the borehole.The subsequent geophysical survey will assist in the <br /> drilling and construction of the other wells in the cluster.After drilling the borehole,drilling mud is <br /> managed according to investigation derived waste(IDV)procedures. <br /> 4.7 Dual Tube Percussion <br /> Similar to the air rotary casing drive method, this method is effective for drilling borings for the <br /> construction of monitoring wells when continuous core and geophysical logs are not required.The <br /> potential for contaminant migration in borehole liquids is diminished by this method.The dual tube <br /> percussion method utilizes small diameter drill pipe and larger diameter drive casing with high pressure <br /> air as the circulating medium.Air is forced down the annular space between the inner drill pipe and outer <br /> drive casing and cuttings are returned to the surface up the inside diameter of the drill pipe.The drill pipe <br /> is advanced by repeated blows of an aboveground percussion hammer. Impact from the hammer is <br /> applied to the outer drive casing only;therefore,very little space exists between the outer drive casing <br /> and surrounding formation(soil).The drive casing keeps the borehole open and as in the air rotary casing <br /> drive method,diminishes the potential for cross contamination of water-bearing zones.The cuttings are <br /> discharged into a cyclonic separator,which separates the air from the formation cuttings to facilitate <br /> sampling and containment of drill cuttings.Groundwater produced during drilling is collected in a tank <br /> and transported from the drill site in a vacuum truck. The rate of penetration depends on the type of <br /> subsurface formation, size of hole, size of the drive casing, and the volume of air forced down the drill <br /> pipe. <br /> field QAPP_DOC 4-3 May 2000 <br />