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76(Former BP)Service Station No. 11193
<br /> S- ECOR
<br /> S.lCEHD
<br /> August 30,2007
<br /> Page 2
<br /> due to the sand unit encountered in the lower portion of well MW-1, and may not be
<br /> representative of the material in the saturated zone (Alisto, 1995). Revised calculations of
<br /> hydrogeologic parameters were submitted in October 1995. Resulting hydraulic conductivity(K)
<br /> values for wells MWA, MW-2, and MW-5:ranging:from 2.25x10"4 to 8.68x10-5 centimeters per
<br /> second (cmis)were within the lower range of expected K values associated with the soil types
<br /> encountered beneatli the site (1 to 1x10-5cmis, Freeze and Cherry, 1979),which consisted of
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<br /> silt and silty sand underlain by fine to medium sand (Alisto, 1995). f
<br /> Between December 10 and 22, 1998, Gettler-Ryan Incorporated(GRI)supervised the removal
<br /> of two 10,000-gallon USTs and one 8,000=gallon'$ingle-walled UST,dispensers,and associated
<br /> product dispenser"piping.. Laboratory analysis of soil samples collected from the UST
<br /> excavation indicated maximum concentrations of GRO at 31 ppm, benzene at 0.27 ppm, and
<br /> MtBE at 80 ppm. Laboratory analysis of soil samples collected from the beneath the dispensers
<br /> and product piping indicated maximum.concentrations of GRO at 1,600 ppm and MtBE at 1.8
<br /> ppm., Approximately.15,000 gallons of water were removed from the excavation during the
<br /> installation of the new USTs. Laboratory analysis of a grab groundwater,sample indicated
<br /> maximum concentrations of GRO, benzene, and MtBE at 17,000 micrograms per liter(pg/Q,
<br /> 1,500 [Lg/L, and 120,000 gg/L, respectively. Well MWA was destroyed to allow for the
<br /> enlargement of the''existing UST excavation for the installation,of the new USTs (GRI, 1999).
<br /> On October 7 and 8, 1999, Cambria Environmental Technology, Incorporated (Cambria)
<br /> conducted a Cone:Penetrometer Testing(CPT)`investigation by advancing six borings (CB-1
<br /> through CB-6) for soil and groundwater 'sampling, and two borings (CB-2E and CB-4E) for
<br />` logging subsurface'soil. Water samples were collected using a hydropunch sampling device at
<br /> depths of 16 and 29 ft bgs in borings CB-1, CB-2, and CB-4 through CB-6. Water samples were
<br /> collected at depths'of 16 and 29 ft bgs in boring CB-3. Gasoline range organics, MtBE, and
<br /> tertiary amyl methyl ether`(TAME) were detected in soil at maximum concentrations of 27
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<br /> milligrams per kilogram (m. Ik9), 27 mg/kg, and 0.058 mg/kg, res ectivel . Groundwater
<br /> samples containe&maximum concentrations of GRO at 87,000 fig&(CB-4-16HP), benzene at
<br /> 1,300 µg/L (CB-4-1,6HP), MtBE at 38,000 µg/l_ (CB-1-16HP), and TAME at 160 µglL (CB-1-
<br /> 16HP, Cambria, 1999). .-
<br /> Also in late 1999, Cambria conducted a sensitive receptor survey. Based on a review of United
<br /> States Geolog icaC Survey (USGS) topographic maps and area maps, an unnamed levy-
<br /> restricted slough was identified 2,000 ft south of the site, and a man-made lake was located in a.
<br /> residential area approximately 1,500 ft southwest of the site. Well logs obtained through the
<br /> State of California' Department of Water Resources (DWR) indicated the presence of an
<br /> irrigation well owned by the California Department of Transportation (Cal-Trans), which was
<br /> screened from approximately 214 ft to 350 ft bgs, and located approximately 315 ft west of the
<br /> site (Cambria, 1999). According to Cambria; the Cal-Trans well had been destroyed in
<br /> preparation for reconfiguration of the Interstate 5 and Hammer Lane.interchange (Cambria,
<br /> 2000). According to Mr.. Witzak Gilon of the City 'of Stockton Municipal Water System
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