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f aZ `1 CAMBRIA August 28, 1995 The system was shut down on March 9, 1998 due to low hydrocarbon removal rates SYSTEM DESIGN Vapor Extraction Wells As previously discussed, GTI supervised the drilling of four 12-inch diameter soil borings to a depth of forty feet Two vapor extraction wells were nested in each boring The screened intervals were positioned at approximate depths of 15 to 25 feet below ground surface (bgs) for wells VEW-IA, VEW-2A, VEW-3A, and VEW-4A, and 30 to 40 feet bgs for wells VEW-113, VEW-213, VEW-313, and VEW-413 GTI used this well design AFAIhm based on site stratigraphy and to provide vapor extraction from these specific depths GTI selected boring locations in the northeastern part of the site based on the defined area of petroleum hydrocarbon impact and an assumed minimum 20-foot radius of vacuum influence Boring logs are provided in Appendix A SVE Equipment SEACOR specified equipment based on GTIs Soil Vapor Extraction Pilot Test The pilot test was conducted to determine the radius of influence from the vapor extraction wells, and the concentration of hydrocarbons in the extracted soil vapor GTI reported an average radius of influence of approximately 40 feet, and concluded that a 20 cubic feet per minute (cfm) flow rate will produce approximately a 25-foot radius of influence The average concentrations of vapors extracted from all the wells was approximately 11,500 micrograms per liter (gg/L) TPHg and 200 gg/L benzene Using the pilot test results as design parameters, SEACOR specified an AKI Systems Inc thermal oxidizer (thermox) with a 600 cfm Lampken extraction blower Additionally, the thermox was equipped with a 200 cfm blower to supplement oxygen for proper combustion The total capacity of the system was 800 cfm The thermox was specified to operate at a temperature of approximately 1,400 degrees Fahrenheit, and was equipped with automatic controls to insure operation within the permitted parameters The extracted soil vapor was conveyed underground through two-inch diameter Schedule 40 polyvinyl chloride (PVC) pipe The individual extraction lines were manifolded in the treatment compound Prior to the manifold, gate valves and sample ports allow independent regulation of the air flow and independent sampling of the vapor streams from each well Access holes with threaded plugs on each soil vapor line provide locations for independent measurement of flow rate with appropriate instrumentation The SVE system design drawings are provided in Appendix B 2