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S E C O R
<br /> 76 Station 11195
<br /> September 13, 2004
<br /> Page 3
<br /> MtBE, and 460 and 870 ppb of tert-amyl methyl ether (TAME), respectively (Gettler-Ryan
<br /> Inc., UST and Product Line Replacement Report, dated April 23, 1999).
<br /> Approximately 61,000 gallons of groundwater were removed from the former and present
<br /> UST pits during the 1998 construction activities, and transported by Waste Management
<br /> Industrial Services (WMIS) of Benicia, California, to the Tosco Refinery in Rodeo, California,
<br /> for disposal.
<br /> Prior to backfilling and compacting of the former gasoline UST complex excavation, one
<br /> conductor casing was placed near the northwest corner of the former UST excavation. The
<br /> casing was installed to facilitate the removal of groundwater from within the former UST
<br /> cavity. The conductor casing consisted of 11.5 feet of 6-inch diameter polyvinyl chloride
<br /> (PVC) and 10 horizontal feet of 6-inch PVC in an "L" configuration extending eastward from
<br /> the vertical section. The bottom 10 feet of the vertical casing and the horizontal casing
<br /> consisted of 0.02-inch machine slotted well screen. The location of the conductor casing is
<br /> shown on Figure 2.
<br /> Between February 26 and March 26, 1999, approximately 41,760 gallons of groundwater
<br /> => were removed from the former UST backfill utilizing the conductor casing. Groundwater
<br /> E _ removal and transportation was performed by WMIS. The water was transported to the
<br /> Tosco Refinery for treatment and disposal. A total of approximately 102,760 gallons of
<br /> groundwater were removed from the former and present UST pits and transported to the
<br /> Tosca Refinery between January 1999 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-
<br /> WS on a weekly basis. The purged groundwater is transported to the Tosca Refinery in
<br /> Rodeo, California for disposal. As of July 29, 2002, Onyx has removed a total of 570,320
<br /> gallons of groundwater from the site.
<br /> In February 2002, GR advanced five offsite geoprobe soil borings (B-1 through B-5)
<br /> downgradient of the subject site. Soil and groundwater samples were collected at each of
<br /> the geoprobe locations and analyzed for TPHg (by EPA Method 8015 modified), and
<br /> benzene, toluene, ethylbenzene, and xylenes (BTEX) and MtBE by EPA Method 8021. In
<br /> addition, all soil and groundwater samples were analyzed for Ethanol, TBA, MtBE, di-
<br /> isopropyl ether (DIPE), ethyl tert-butyl ether (ETBE), 1,2-dichloroethane (1,2 DCA), TAME,
<br /> and ethylene dibromide (EDB) by EPA Method 8260B. None of the hydrocarbon
<br /> constituents were detected in soil. Four groundwater samples (B-1, B-2, B-4, and B-5)
<br /> contained MtBE at concentrations ranging from 3.0 to 10,000 ppb.
<br /> On May 28 and 29, 2002, GR installed five additional offsite groundwater monitoring wells
<br /> (MW-13 through MW-17) at the locations shown on Figure 2. The well borings were drilled
<br /> to depths ranging from 20 to 21 feet bgs. Groundwater was encountered in the well borings
<br /> during drilling at depths ranging from approximately 8 to 10 feet bgs. All soil samples
<br /> CP 11195 Assessment WP 9-04.doc SECOR Intemationat Incorporated
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