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rK n • 16 April 1997 AGE -NC Project No 95-0121 Page 3 of 9 2 4 GROUND WATER DEPTH AND FLOW DIRECTION Between 1991 and 1997, the water -table surface beneath the site has generally decreased from approximately 33 feet to 18 feet bsg The uppermost ground water flows in a unconfined aquifer With increasing depth, the aquifer becomes semi -confined due to the presence of mixed heterogeneous layers of sediments Between 1991 and 1997, ground water monitoring data at the site remained relatively constant with a general ground water flow direction towards the northeast Relative ground water elevation maps for the site have been included in previous Quarterly Reports prepared by AGE 3 0. SCOPE OF WORK An SVE system in conjunction with an IAS system is proposed within the "core" petroleum hydrocarbon -impacted area at the site In order to maximize the efficiency of the clean-up efforts, a 24-hour operation of the system is planned A typical destruction rate of greater than 95% of hydrocarbon vapors is expected throughout the entire cleanup duration 3 1 PROPOSED SOIL VAPOR EXTRACTION SYSTEM DESIGN A thermal destruction process is proposed for hydrocarbon vapor recovery by utilizing a direct fired thermal oxidizer vapor extraction system (VES) A typical diagram of the system is illustrated in Figure 3 - Proposed Soil Vapoi Extraction System The VES will be connected through a manifold box to the vapor recovery wells and should be able to operate between 225 and 250 cubic feet per minute (cfm) The thermal oxidizer can be outfitted with a catalytic module and/or a heat exchanger to provide an effective destruction ratio at reduced concentrations of hydrocarbon vapor Soil vapors will be extracted from a configuration of extraction wells using a vacuum blower and routed to the thermal oxidizer Supplemental fuel (i a natural gas) will be added to maintain the optimal temperature for a maximum destruction rate of hydrocarbon vapors Additional information on the proposed system is included with Appendix A 3 1 1 PROPOSED SOIL VAPOR EXTRACTION WELLS Installation of five SVE wells is proposed within the "core" petroleum hydrocarbon -impacted area Installation of SVE wells will be completed utilizmg a truck mounted, hollow stem drill rig and 8 -inch hollow stem augers Furthermore, the SVE system will consist of the five newly installed SVE wells and the two existing SVE wells located near the former UST area The proposed SVE well locations