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11 August_1997 off AGE-NC Project No. 95-0118 Page 3 of 9 derived from both marine and non-marine sediment, and are generally formed in alluvium derived from mixed rock sources. 2.4. GROUND WATER DEPTH AND FLOW DIRECTION Ground water is currently encountered at a depth of approximately 35 feet bsg and has a dominant northwesterly flow direction. Ground water occurs in a generally sandy layer extending from approximately 30 feet to 45 feet bsg. The uppermost ground water flows in an unconfined aquifer. With increasing depth, the aquifer becomes semi-confined due to.the presence of mixed heterogeneous layers of sediments. The sedimentary units.are relatively horizontal and continuous over the site. 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 the recommended method of remediation for the petroleum hydrocarbons at the site. In order to maximize the efficiency of the clear,,-up efforts, a 24-hour operation of the system is planned. A typical destruction rate of greater than 97% of hydrocarbon vapor can be 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 -Diagram of Proposed Vapor Extraction System. The VES will be connected through a pipe manifold to the vapor recovery wells and should be able to operate between 150 and 200 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 vapor will be extracted from a configuration of extraction wells using a vacuum blower and routed to the thermal oxidizer. Supplemental fuel (i.e. natural gas) will be added to maintain'the optimal temperature for a maximum destruction rate of hydrocarbon vapor. Additional information on the proposed soil vapor extraction unit is included in Appendix A. Advanced GeoEnvironmental,Inc.