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<br /> 76 Service Station#11195
<br /> April 5, 2004
<br /> Page 2
<br /> with neat cement placed by the use of a grout pump and tremie pipe. The well destruction was
<br /> permitted and observed by the PHS-EHD.
<br /> Five offsite wells (MW-8 through MW-12) were installed and one offsite well (MW-7) was destroyed in
<br /> September 1998. Soil samples collected during the investigation at depths of 4 to 6 feet bgs contained
<br /> petroleum hydrocarbon concentrations of up to 1.5 ppm of TPHg and 0.0034 ppm of benzene.
<br /> Oxygenating compounds including methyl tert-butyl ether(MtBE)were not detected (Alisto, 1999).
<br /> A sensitive receptor survey and a'/-mile radius water well survey were performed by Alisto in 1999. No
<br /> basements or subways were found within a 300-foot radius of the subject site. An offsite subsurface
<br /> utility survey revealed the presence of a sanitary sewer trench adjacent to the subject site that may
<br /> influence the transport of petroleum hydrocarbons in groundwater. A search of California Department of
<br /> Water Resources (DWR) and Banks Information Solutions files indicated that seven water wells had
<br /> been installed within a %-mile radius of the subject site, however, the wells could not be located based
<br /> upon the information provided by DWR. A visual reconnaissance of the area did not identify the
<br /> presence of any additional water wells(Alisto, 1999).
<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-
<br /> wall gasoline USTs, two dispenser islands, related product lines, and one canopy in December 1998.
<br /> - The new USTs were installed in an excavation located immediately adjacent to the former UST
<br /> =` complex. These excavations are hydraulically connected with pea gravel backfill material encountered
<br /> in the northeast 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
<br /> to 12 feet bgs contained petroleum hydrocarbons at concentrations of up to 130 ppm of TPHg, 50 ppm
<br /> of MtBE, 290 ppm of ethanol, and 51 ppm of tertiary butyl alcohol (TBA). All of the soil samples were
<br /> non-detect for benzene and the oxygenate compounds. Soil samples collected from beneath the former
<br /> product lines at depths of 3 to 4 feet bgs were non-detect for TPHg, benzene, MtBE, or the six
<br /> oxygenate compounds. A set of first generation product lines were discovered during construction
<br /> activities and removed. Soil samples were collected from beneath these product lines at depths of 2.5
<br /> to 4 feet bgs. Concentrations of TPHg (50 ppm), MtBE (0.17 ppm), and ethanol(64 ppm)were reported
<br /> in these samples. The area surrounding these samples was overexcavated and four sidewall soil
<br /> samples and one bottom sample were collected at depths ranging from 6 to 11.5 feet bgs. These
<br /> samples contained TPHg 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
<br /> grab groundwater samples were collected from the former UST excavation and analyzed for TPHg,
<br /> BTEX, MtBE, and six oxygenate compounds. Grab groundwater samples SW and CW, collected from
<br /> beneath the former south and center USTs, contained 8,400 and 60,000 ppb of TPHg, 310 and 1,500
<br /> ppb of benzene, 100,000 and 130,000 ppb of MtBE, and 460 and 870 ppb of tert-amyl methyl ether
<br /> (TAME), respectively (Gettler-Ryan Inc., UST and Product Line Replacement Report, dated April 23,
<br /> 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 /> I:1ConocoPhillips1111951Work Plan For Reinstallation Of MW-13.Doc
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