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<br /> In December 1994, Emcon advanced soil borings TB-1 through TB-3 to 20 feet bgs and TB-4 to
<br /> 71 feet bgs. Concentrations of benzene (0.18 parts per million [ppm]), toluene (0.005 ppm),
<br /> ethylbenzene (0.031 ppm), and xylenes (0.040 ppm) were detected in the soil sample collected
<br /> from TB-4 at 65 feet bgs. Xylenes were detected at 0.005 ppm in TB-2 at 20 feet bgs. Total
<br /> petroleum hydrocarbons as oil and grease (TOG) was detected in soil samples from TB-1 at 10
<br /> feet bgs, TB-3 at 10 and 20 feet bgs, and TB-4 at 65 feet bgs (EMCON, 1994).
<br /> Based on a March 19, 1996 letter from the California Regional Water Quality Control Board
<br /> (RWQCB) —Central Valley Region, the site (then BP Station No.11190) was granted No Further
<br /> Action status.
<br /> In preparation for sale of the site, in March 2005, SECOR International (SECOR) advanced six
<br /> soil borings (B-1 through B-6) at the site. TPHg, TPHd, benzene, methyl tert-butyl ether (MTBE)
<br /> and tert-butyl alcohol (TBA) concentrations were reported as maximum concentrations of 1,600
<br /> milligrams per kilograms (mg/kg), 1,300 mg/kg, 3 mg/kg, 6.3 mg/kg, and 0.47 mg/kg, respectively
<br /> (SECOR, 2005).
<br /> In January 2007, SECOR observed the drilling of soil borings B-7 through B-11 to depths of 50 to
<br /> 55 feet bgs in the vicinity of the existing UST's and gasoline dispensers. Gasoline-range organics
<br /> (GRO [ aka TPHg]), diesel range organics (DRO [aka TPHd]), and benzene were only detected
<br /> in soil boring B-7, at concentrations of 8,000 mg/kg, 32 mg/kg, and 25 mg/kg, respectively. MTBE
<br /> was reported in several borings at a maximum concentration of 8.0 mg/kg (B-11@50').
<br /> Groundwater was encountered in two borings, B-7 and B-11 at depths of 45 to 47 feet bgs and
<br /> groundwater samples were collected. GRO and BTEX were detected at concentrations of up to
<br /> 6,000 pg/L, 150 pg/L, 970 pg/L, 200 pg/L and 1,000 pg/L, respectively in the groundwater sample
<br /> collected from B-7. The highest MTBE and TBA concentrations (60,000 pg/L and 7,700 pg/L,
<br /> respectively) were detected in the groundwater sample collected from B-11 (SECOR, 2007).
<br /> In March 2008, SECOR supervised the installation of on-site groundwater monitoring wells MW-
<br /> 1 through MW-4 to a total depth of approximately 55 feet bgs (SECOR, 2008).
<br /> In February 2010, Stantec (formerly SECOR) oversaw the installation of monitoring wells MW-5
<br /> through MW-9 to an approximate depth of 65 feet bgs. MTBE was detected in soil samples
<br /> collected from wells MW-6 through MW-9, with a maximum concentration of 6.8 mg/kg in soil
<br /> sample MW-7@62, while TBA was detected in soil samples collected from well MW-7 at a
<br /> maximum concentration of 1.2 mg/kg (Stantec, 2010).
<br /> In June 2016, ATC oversaw the installation of off-site monitoring well MW-10 to an approximate
<br /> depth of 65 feet bgs. Petroleum hydrocarbons were not detected in soil and groundwater samples
<br /> collected from off-site monitoring well MW-10.
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