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Groundwater Monitoring Well Installation and Ozone Microsparge System Installation and Startup Report— ConocoPhillips(76)Service Station No. 11195,Lathrop,California May 20,2003 the soil samples were non-detect for benzene and the oxygenate compounds. Soil samples collected from beneath the former product lines at depths of 3 to 4 feet bgs were non-detect for TPHg, benzene, MtBE, or the six oxygenate compounds. A set of first generation product lines were discovered during construction activities and removed. Soil samples were collected from beneath these product lines at depths of 2.5 to 4 feet bgs. Concentrations of TPHg(50 ppm),MtBE (0.17 ppm), and ethanol (64 ppm) were reported in these samples. The area surrounding these samples was overexcavated and four sidewall soil samples and one bottom sample were collected at depths ranging from 6 to 11.5 feet bgs. These samples contained TPHg concentrations up to 950 ppm,but were non-detect for all other analytes. Groundwater was encountered in the excavations at a depth of approximately 11 to 12 feet bgs. Two grab groundwater samples were collected from the former UST excavation and analyzed for TPHg, benzene, toluene, ethylbenzene, and total xylenes (BTEX), MtBE, and six oxygenate compounds. Grab groundwater samples SW and CW, collected from beneath the former south and center UST's, contained 8,400 and 60,000 ppb of TPHg, 310 and 1,500 ppb of benzene, 100,000 and 130,000 ppb of MtBE, and 460 and 870 ppb of tert-amyl methyl ether (TAME), respectively (Gettler-Ryan Inc., UST and Product Line Replacement Report, dated April 23, 1999). Approximately 61,000 gallons of groundwater were removed from the former and current UST pits during the 1998 construction activities, stored on-site in portable tanks, then transported by Waste Management Industrial Services (WMIS) of Benicia, California, to the Tosco Refinery in Rodeo, California, for treatment and disposal. Prior to backfilling and compacting of the former gasoline UST complex excavation, one conductor casing was placed near the northwest corner of the former UST excavation. The casing was installed to facilitate the removal of groundwater from within the former UST cavity. The conductor casing consisted of 11.5 feet of 6-inch diameter polyvinyl chloride (PVC) and 10 horizontal feet of 6-inch PVC in an"L" configuration extending eastward from the vertical section. The bottom 10 feet of the vertical casing and the horizontal casing consist of 0.02-inch machine slotted well screen. The location of the conductor casing is shown on Figure 2. Between February 26 and March 26, 1999, approximately 41,760 gallons of groundwater were removed from the former UST backfill utilizing the conductor casing. Groundwater removal and transportation was performed by WMIS. The water was transported to the ConocoPhillips Refinery for treatment and disposal. Starting in January of 2000, weekly groundwater purging was conducted by Onyx Industrial Services of Benicia California. Approximately 5,000-gallons of groundwater was purged from the conductor casings and monitoring wells MW-3, MW-5 and MW- 10 during each event. As of December of 2002, approximately 886,820-gallons of groundwater have been purged from the site and disposed of at the ConocoPhillips Refinery in Rodeo, California. 140193.14-2 4