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:- Interim Corrective Action Plan—Tosco(76)Service Station No. 11195,Lathrop, California
<br /> LA st 28 2002
<br /> One 10,000-gallon, one 8,000-gallon, and one 6,000-gallon single-wall fiberglass gasoline USTs, two
<br /> dispenser islands,related product lines,and one canopy were replaced with two 12,000-gallon double-wall
<br /> gasoline USTs,two dispenser islands,related product lines,and one canopy in December 1998. The new
<br /> USTs were installed in an excavation located immediately adjacent to the former UST complex. These
<br /> excavations are hydraulically connected with pea gravel backfill material encountered in the northeast
<br /> corner of the former UST pit.
<br /> Soil samples collected from the capillary fringe of the former and new UST excavations at depths of 11 to
<br /> 12 feet bgs contained petroleum hydrocarbons at concentrations of up to 130 ppm of TPHg, 50 ppm of
<br /> MtBE,290 ppm of ethanol,and 51 ppm of tertiary butyl alcohol(TBA). All of the soil samples were non-
<br /> detect for benzene and the oxygenate compounds. Soil samples collected from beneath the former product
<br /> lines at depths of 3 to 4 feet bgs were non-detect for TPHg, benzene, MtBE, or the six oxygenate
<br /> compounds. A set of first generation product lines were discovered during construction activities and
<br /> removed. Soil samples were collected from beneath these product lines at depths of 2.5 to 4 feet bgs.
<br /> Concentrations of TPHg (50 ppm), MtBE (0.17 ppm), and ethanol (64 ppm) were reported in these
<br /> samples. The area surrounding these samples was overexcavated and four sidewall soil samples and one
<br /> bottom sample were collected at depths ranging from 6 to 11.5 feet bgs. These samples contained TPHg
<br /> concentrations up to 950 ppm,but were non-detect for all other analytes.
<br /> Groundwater was encountered in the excavations at a depth of approximately 11 to 12 feet bgs. Two grab
<br /> groundwater samples were collected from the former UST excavation and analyzed for TPHg, BTEX,
<br /> Z1, and six oxygenate compounds. Grab groundwater samples SW and CW,collected from beneath
<br /> the former south and center USTs, contained 8,400 and 60,000 ppb of TPHg, 310 and 1,500 ppb of
<br /> benzene, 100,000 and 130,000 ppb of MtBE, and 460 and 870 ppb of tert-amyl methyl ether(TAME),
<br /> respectively (Gettler-Ryan 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 UST pits during
<br /> the 1998 construction activities, and transported by Waste Management Industrial Services (WMIS) of
<br /> 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 casing
<br /> was placed near the northwest corner of the former UST excavation. The casing was installed to facilitate
<br /> the removal of groundwater from within the former UST cavity. The conductor casing consisted of 11.5
<br /> feet of 6-inch diameter polyvinyl chloride (PVC) and 10 horizontal feet of 6-inch PVC in an "L"
<br /> configuration extending eastward from the vertical section.The bottom 10 feet of the vertical casing and
<br /> the horizontal casing consisted of 0.02-inch machine slotted well screen. The location of the conductor
<br /> casing is shown on Figure 2.
<br /> Between February 26 and March 26, 1999,approximately 41,760 gallons of groundwater were removed
<br /> from the former UST backfill utilizing the conductor casing. Groundwater removal and transportation was
<br /> performed by WNIIS. The water was transported to the Tosco Refinery for treatment and disposal. A total
<br /> of approximately 102,760 gallons of groundwater were removed from the former and present UST pits and
<br /> transported to the Tosco Refinery between January 1999 and March 26, 1999.
<br /> 140193.13 3
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