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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 />