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Ms. Margaret Lagorio September 24, 1996 Page 6 concentrations in groundwater have not been detected, except for some intermittent occurrences of very low concentrations as explained previously. Therefore, it appears the SVETS was effective in removing the residual hydrocarbons from the soil as a result of the fluctuating groundwater levels beneath the Site. The approximate mass of benzene and TPH-G in the groundwater was calculated. The extent of benzene and TPH-G in groundwater was based on concentrations. The approximate mass of benzene and TPH-G calculated is 0.001 and 0.10 pounds, respectively, in October 1992, just prior to the GWETS start-up. During the operation of the GWETS, from October 1992 to April 1993, a total of 0.0003 pounds and 0.01 pounds of benzene and TPH-G were removed, respectively (Table 5). Based on these calculations, the amount of pounds removed in the groundwater does not exceed the available amount. The amount available is very minor and is not a significant risk to groundwater. Mass balance calculations for groundwater are included as Exhibit D. Remediation The remediation system at ARCO Facility 434 consists of a SVETS. The SVETS was shut down in February 1996, because of low influent concentrations. A GWETS, which was formerly in use at the site, was shut down on April 19, 1993, due to nondetectable concentrations of hydrocarbons in the groundwater. SVETS. The SVETS consists of eight soil vapor extraction wells (VE-1 through VE-8) and a soil vapor treatment system. The soil vapor treatment system is composed of a vacuum compressor pump connected to a bio-remediation filter with a design treatment flow rate of 100 cubic feet per minute of vapor. The bio-filter system operated from May 1995 through September 1995. When in operation, the system operated under Authority to Construct No. N-1081-1-1 issued by the San Joaquin Valley Unified Air Pollution Control District. During operation, influent concentrations of TPH-G and benzene were generally declining, indicating that hydrocarbons in the site soil were being successfully remediated. The radius of influence for the SVETS was determined during a soil vapor extraction test performed on June 27, 1990. The radius of influence is approximately 85 feet as shown on Figure 7. A summary of the pilot test results is discussed in BC's Results of Soil Vapor Extraction System Pilot Test-- ARCO Station 434, Lodi, California, dated July 5, 1990. GWETS. When in operation (October 14, 1992 to April 19, 1993) the GWETS consisted of extracting groundwater from extraction well E-1 with a designed pumping capacity of 1 gallon per minute. The extracted groundwater was treated through two, 1,000-gallon capacity granular activated carbon vessels. The treated water was discharged to the industrial sewer. Industrial Waste Discharge Permit No. 151 regulated the discharge to the industrial sewer. • Use or disclosure of data continued on this sheet is subject to the restriction specified at the beginning of this document. 3382TORRESFICLOSURE.DOC