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16 April 1997 <br /> AGE-NC Project No . 95 -0121 <br /> Page 3 of 9 <br /> 2 . 4 . GROUNDWATER DEPTH AND FLOW DIRECTION <br /> Between 1991 and 1997, the water-table surface beneath the site has generally decreased from <br /> approximately 33 feet to 18 feet bsg . The uppermost ground water flows in a unconfined aquifer. <br /> With increasing depth, the aquifer becomes semi- confined due to the presence of mixed <br /> heterogeneous layers of sediments. <br /> Between 1991 and 1997, ground water monitoring data at the site remained relatively constant with <br /> a general ground water flow direction towards the northeast. Relative Rround water elevation maps <br /> for the site have been included in previous Quarterly Reports prepared by AGE. <br /> Me SCOPE OF WORK <br /> An SVE system in conjunction with an IAS system is proposed w;thin the "core" petroleum <br /> hydrocarbon-impacted area at the site. In order to maximize the efficiency of the clean-up efforts, a <br /> 24 - hour operation of the system is planned . A typical destruction rte of greater than 95% of <br /> hydrocarbon vapors is expected throughout the entire cleanup duration <br /> 3 . 1 . PROPOSED SOIL VAPOR EXTRACTION SYSTEM DESIGN <br /> A thermal destruction process is proposed for hydrocarbon vapor recd% ery by utilizing a direct fired <br /> thermal oxidizer vapor extraction system (VES) . A typical diagram of the system is illustrated in <br /> Figure 3 - Proposed Soil 6apor Exlrncrion System. <br /> The VES will be connected through a manifold box to the vapor recovery wells and should be able <br /> to operate between 225 and 250 cubic feet per minute (cfm) . The thermal oxidizer can be outfitted <br /> with a catalytic module and/or a heat exchanger to provide an effective destruction ratio at reduced <br /> concentrations of hydrocarbon vapor. Soil vapors will be extracted from a configuration of extraction <br /> wells using avacuum blower and routed to the thermal oxidizer. Supplemental fuel (i. e. natural gas) <br /> will be added to maintain the optimal temperature for a maximum destruction rate of hydrocarbon <br /> vapors. Additional information on the proposed system is included with Appendix A. <br /> 3 . 1 . 1 . PROPOSED SOIL VAPOR EXTRACTION WELLS <br /> Installation of five SVE wells is proposed within the "core" petroleum hydrocarbon-impacted area. <br /> Installation of SVE wells will be completed utilizing a truck mounted, hollow stem drill rig and 8-inch <br /> hollow stem augers. Furthermore, the SVE system will consist of the five newly installed SVE wells <br /> and the two existing SVE wells located near the former UST area. The proposed SVE well locations <br />