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Description of the Arrangement of the Dual Phase Extraction Well <br /> and the Extraction Tube <br /> As described above, and shown in Drawing M-2, the dual-phase <br /> extraction well is a soil vapor and ground water recovery well which is <br /> screened across both the vadose and saturated zones. The dual phase <br /> extraction well includes an interior extraction tube which supplies <br /> vacuum to the dual phase extraction well. The screened interval above <br /> the ground water surface facilitates soil vapor extraction from the vadose <br /> zone. During dual phase extraction, the depth of the extraction tube <br /> within the dual phase extraction well is adjusted such that the desired <br /> ratio of soil vapor and ground water is extracted. <br /> Typically, for simultaneous extraction of vapor and liquid, the extraction <br /> tube is placed less than 6 inches above the static water table. However, if <br /> the extraction tube is placed too close to the water table, or if the <br /> extraction tube is placed beneath the water table, only ground water may <br /> enter the extraction tube, depending on the ground water recharge rate <br /> into the dual phase extraction well. Therefore, the positioning of the <br /> extraction tube is critical for the simultaneous extraction of both soil vapor <br /> and liquid. Any floating product at the water table surface is also <br /> withdrawn with ground water. The procedures that will be implemented <br /> to determine the appropriate placement of the extraction tubes within the <br /> dual phase extraction wells at the site are discussed in Section 6 - <br /> Operation and Monitoring of the Remedial Action. <br /> Conceptual Plan for Dual Phase Extraction at the Tracy Yard <br /> During dual phase extraction at the site, the base of the extraction tube <br /> will be placed immediately above the water table. When vacuum is <br /> applied to the extraction tube, the water table level within the extraction <br /> well will increase, such that ground water will enter the extraction tube. <br /> Soil vapor will also enter the extraction tube via the screened interval of <br /> the dual phase extraction well within the vadose zone. Because ground <br /> water and soil vapor enter the extraction tube simultaneously, the ground <br /> water travels through the extraction tube in a turbulent condition. This <br /> turbulent condition causes ground water to enter and rise through the <br /> extraction tube as water droplets. <br /> The rate that ground water and soil vapor are extracted is controlled by <br /> the amount of vacuum applied to the extraction tube and the vertical <br /> position of the extraction pipe relative to the ground water surface. In the <br /> 3-2 <br />