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CA ARNG Field Quality Assurance Project Plan hollow stem. A pilot bit at the bottom is used to plug the hollow core of the augers during drilling unless coring is performed. Cuttings are returned to the surface along the continuous flights, removed from the borehole location with a shovel, and placed in an appropriate container. 4.3.3 If a bottom plug is not used or is removed for well construction, water may be added to the hollow stem of the auger flights during drilling operations to limit the movement of silts and sands into the bottom of the auger flights. The volume of water added into the hollow stem during pilot hole drilling and well construction will be monitored and recorded. If the boring is to be used for well construction, the volume of water added during drilling will be removed during well development. 4.4 Air Rotary Casing Drive 4.4.1 Also called air rotary casing hammer (ARCH), this method of borehole drilling is preferred at locations where drifling mud is not required for geophysical logging, a monitoring well will be constructed, and potential for downward migration of contaminated groundwater in the boring exists during drilling. The method is cost effective for producing borings for well construction when continuous core and geophysical logs are not required. 4.4.2 The ARCH technique involves constructing a borehole by advancing a nonrotating, threaded casing with a retractable pneumatic hammer while simultaneously drilling a slightly smaller diameter boreholewithfiltered air forced downward through the center drill rod to the -bit. The air returns upward through the annulus between the drive casing and the smaller rotating drill rod bringing with it a continuous discharge of drill cuttings. A water mist injection is used if necessary to assist the drilling and cuttings recovery rate. The material is discharged into a cyclone arrangement that separates the air from the formation cuttings to facilitate sampling and drill cutting containment. 4.5 GeoprobeO The Geoprobe® System (or other direct push technology) is an effective technique for continuous core continuous core characterization of unconsolidated soils at depths of less than 15 feet. In addition to obtaining core samples, the Geoprobe can also be modified to collect soil vapor, soil, and groundwater samples at deeper depths. The Geoprobe assembly consists of a hydraulically powered percussion hammer mounted in a truck or van. Sampling tools and rods between 1.0 -inch and 1.6 -inch outer diameter (OD), are advanced into the ground by the application of weight and percussion with no cuttings being generated. The soil core is obtained by tripping the tool string out of the hole and extracting the soil from the sample tube so the field geologist can log it. 4.6 Direct Circulation Mud Rotary The direct circulation mud rotary drilling method employs a bit that attaches to the lower end of a drill pipe and advances the boring as the drill pipe is rotated. In direct circulation rotary drilling, a drilling mud is pumped down through the drill pipe and out through the ports or jets in the drill bit. The mud consists of a mixture of water and bentonite powder. The mud then flows upward in the annular space between the hole and drill pipe, and carries the cuttings in suspension to the surface. At the surface, the mud is channeled across a shaker, and then into a settling pit or pits where most of the remaining cuttings drop out. The mud is then recirculated back down the borehole. The functions of the mud are to: transport the cuttings, support and stabilize the borehole, seal the borehole to prevent fluid loss, allow the cuttings to be separated at the surface, cool and clean the bit, and lubricate the bit. The mud weight and viscosity will be monitored and recorded at the start of drilling each day and at two-hour intervals during drilling unless mud conditions (e.g., increased or decreased viscosity, etc.) or drilling conditions (e.g., field QAPP.DOC 4-2 May 2000