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S E C O R
<br /> samples were non-detect for benzene and the oxygenate compounds. Soil samples collected from
<br /> beneath the former product lines at depths of 3 to 4 feet bgs were non-detect for TPHg, benzene,
<br /> MtBE, or the six oxygenate compounds. A set of first generation product lines were discovered
<br /> during construction activities and removed. Soil samples were collected from beneath these
<br /> product lines at depths of 2.5 to 4 feet bgs. Concentrations of TPHg (50 ppm), MtBE (0.17 ppm),
<br /> and ethanol (64 ppm) were reported in these samples. The area surrounding these samples was
<br /> overexcavated and four sidewall soil samples and one bottom sample were collected at depths
<br /> ranging from 6 to 11.5 feet bgs. These samples contained TPHg concentrations up to 950 ppm, but
<br /> were non-detect for all other analytes.
<br /> Groundwater was encountered in the excavations at a depth of approximately 11 to 12 feet bgs.
<br /> Two grab groundwater samples were collected from the former UST excavation and analyzed for
<br /> TPHg, BTEX, MtBE, and six oxygenate compounds. Grab groundwater samples SW and CW,
<br /> collected from beneath the former south and center USTs, contained 8,400 and 60,000 ppb of
<br /> TPHg, 310 and 1,500 ppb of benzene, 100,000 and 130,000 ppb of MtBE, and 460 and 870 ppb of
<br /> tert-amyl methyl ether(TAME), respectively (Gettler-Ryan Inc., UST and Product Line Replacement
<br /> Report, dated April 23, 1999).
<br /> Approximately 61,000 gallons of groundwater were removed from the former and present UST pits
<br /> during the 1998 construction activities, and transported by Waste Management Industrial Services
<br /> (WMIS) of Benicia, California, to the Tosco Refinery in Rodeo, California, for disposal.
<br /> Prior to backfilling and compacting of the former gasoline UST complex excavation, one conductor
<br /> casing was placed near the northwest corner of the former UST excavation. The casing was
<br /> installed to facilitate the removal of groundwater from within the former UST cavity. The conductor
<br /> casing consisted of 11.5 feet of 6-inch diameter polyvinyl chloride(PVC) and 10 horizontal feet of 6-
<br /> inch PVC in an "U configuration extending eastward from the vertical section. The bottom 10 feet of
<br /> ysj the vertical casing and the horizontal casing consisted of 0.02-inch machine slotted well screen.
<br /> The location of the conductor casing is shown on Figure 2.
<br /> Between February 26 and March 26, 1999, approximately 41,760 gallons of groundwater were
<br /> removed from the former UST backfill utilizing the conductor casing. Groundwater removal and
<br /> transportation was performed by WMIS. The water was transported to the Tosco Refinery for
<br /> treatment and disposal. A total of approximately 102,760 gallons of groundwater were removed
<br /> from the former and present UST pits and transported to the Tosco Refinery between January 1999
<br /> and March 26, 1999.
<br /> Starting in January 2000, Tosco contracted Onyx Industrial Services, Inc. (Onyx) of Benicia,
<br /> California to purge approximately 5,000 gallons of groundwater from conductor casing CC-WS on a
<br /> weekly basis. The purged groundwater is transported to the Tosco Refinery in Rodeo, California for
<br /> disposal. As of July 29, 2002, Onyx has removed a total of 570,320 gallons of groundwater from
<br /> the site.
<br /> In February 2002, GR advanced five offsite geoprobe soil borings (B-1 through B-5) downgradient
<br /> of the subject site. Soil and groundwater samples were collected at each of the geoprobe
<br /> locations and analyzed for TPHg (by EPA Method 8015 modified), and benzene, toluene,
<br /> ethylbenzene, and xylenes (BTEX) and MtBE by EPA Method 8021. In addition, all soil and
<br /> groundwater samples were analyzed for Ethanol, TBA, MtBE, di-isopropyl ether(DIPE), ethyl tert-
<br /> butyl ether (ETRE), 1,2-dichloroethane (1,2 DCA), TAME, and ethylene dibromide (EDB) by EPA
<br /> Method 82606, None of the hydrocarbon constituents were detected in soil. Four groundwater
<br /> samples (B-1, B-2, B-4, and B-5) contained MtBE at concentrations ranging from 3.0 to 10,000
<br /> ppb.
<br /> On May 28 and 29, 2002, GR installed five additional offsite groundwater monitoring wells (MW-
<br /> 13 through MW-17) at the locations shown on Figure 2. The well borings were drilled to depths
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