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�e Ms Margaret Lagono S E C ® R August 1, 2005 Page 4 d xylenes beneath the product Imes northeast of the northwest dispenser island at a depth of 4 feet bgs A In November 2001, GR directed the installation of ozone wells SP-1 through SP-10 at approximately 65 feet bgs, and ozone wells SP-11 through SP-13 at approximately 40 feet bgs The wells were connected to an ozone sparge system and the ozone sparge system was placed into operation on December 19, 2001 The system cycles ozonelair infection between 10 sparge points at a time Since the ozone panel is designed to supply ozone to 10 sparge points, wells SP-1 through SP-3 are not currently in operation Sparge point selection and cycle times are adjusted as petroleum hydrocarbon concentrations in groundwater fluctuate During the first quarter 2003, a carbon absorption system was installed to treat off-gas During the third quarter 2003, the SVE system was operated continuously from August 12 through September 18, 2004 Based on flame ionization detector (FID) readings collected during SVE system operation and maintenance (O&M), approximately 12 pounds (lbs) of petroleum hydrocarbons were removed during the quarter The initial influent concentration was 18 parts per million (ppmv) by volume on August 12, but was quickly reduced to non- detectable levels of petroleum hydrocarbons In the third quarter of 2004, it was determined that pulsing of the existing SVE system was no longer a cost effective remedial technology based on non-detectable petroleum hydrocarbons in the system influent San Joaquin County Environmental Health • Department approved removal of the SVE system in their letter dated January 12, 2005 SENSITIVE RECEPTORS According to a 1992 report by RESNA, there is one municipal water-supply well within 2,000 feet of the site, located at the corner of Bidwell Place and Bianchi Road The well is approximately 1,800 feet to the southeast of the site and is maintained by the California Water Service According to the California Water Service, the total depth of the well is 520 feet bgs, with screened intervals of 195 to 240 feet bgs and 260 to 345 feet bgs MONITORING AND SAMPLING The site has been monitored and sampled since first quarter 1990 From 1990 to the present, the site has been monitored and sampled quarterly Currently, 18 wells (MW-1, MW-2, MW-4 through MW-9, MW-11, MW-14 through MW-16, PTW-1, VW-1 through VW-4, and VW-7) are monitored, sampled, and analyzed for TPHg, BTEX and the fuel oxygenates tertiary-butyl alcohol (TBA), methyl tertiary-butyl ether (MtBE), di-isopropyl ether (DIPE), ethyl tertiary-butyl ether (EtBE), tertiary-amyl methyl ether (TAME), 1,2- dichloroethane (1,2-DCA), ethylene di-bromide (EDB), and ethanol by U S Environmental Protection Agency (EPA) Method 8260B DISCUSSION During the second quarter 2005, depth to groundwater in the 18 site wells ranged from approximately 31 04 feet to 34 81 feet below ground surface (bgs), which is consistent , with historical levels that have ranged between depths of 24 19 feet and 52 74 feet bgs r 6981 2Q2005 QSSR doc SECOR tntemationat Incorporated d e�