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<br /> S E C 0 R
<br /> 76 Station No. 11193
<br /> August 13, 2004
<br /> Page 4
<br /> Transportation (Cal-Trans), which was screened from approximately 214 feet to 350 feet
<br /> bgs and located approximately 315 feet west of the site (Cambria, 1999). According to
<br /> Cambria, the Cal-Trans well had been destroyed in preparation for reconfiguration of the
<br /> Interstate 5 and Hammer Lane interchange (Cambria, 2000). According to Mr. Witzak
<br /> Gilon of the City of Stockton Municipal Water System (CSMWS), there were no CSMWS
<br /> water supply wells located within the 2,000-foot search radius (Cambria, 1999).
<br /> On June 12 and 13, 2000, Cambria replaced destroyed Well MW-1 and damaged Well
<br /> MW-2 with Groundwater Monitoring Wells MW-1R and MW-2R to depths of 31.5 and 30
<br /> feet bgs, respectively. In addition, Cambria drilled and installed two 2-inch diameter wells
<br /> (MW-9 and MW-10) to a total depth of 31.5 feet bgs. Laboratory analysis of soil samples
<br /> collected from the soil borings detected maximum concentrations of TPHg at 0.82 mg/kg
<br /> (MW8-12') and MtBE at 2.6 mg/kg (MW8-30). BTEX was not detected above laboratory
<br /> detection limits. Laboratory analysis of groundwater samples collected from all wells
<br /> detected maximum concentrations of TPHg at 3,400 µg/l_ (VW-1), benzene at 84 µg/L
<br /> (VW-1), MtBE at 250,000 pg/L, and tert-butyl alcohol (TBA) at 17,000 84 µg/L (MW-2R)
<br /> (Cambria,2000).
<br /> In August 2000, GR implemented an interim migration control plan at the site to reduce the
<br /> amount of petroleum hydrocarbons and MtBE beneath the site, and to prevent further off-
<br /> site migration of the dissolved plume (GR, 2000). The plan consisted of the periodic
<br /> extraction,of approximately 5,000 gallons of groundwater from wells historically containing
<br /> the highest concentrations of petroleum hydrocarbons and MtBE (MW-1 R, MW-2R, and
<br /> VW-1).
<br /> In November 2001, SECOR conducted a five-day dual-phase extraction (DPE) test to
<br /> reduce the amount of petroleum hydrocarbons in soil and groundwater beneath the site,
<br /> and to determine the feasibility of DPE as an applicable technology for remediation at the
<br /> site. DPE tests were performed on well MW-1 R for 3 hours, MW-2R for 3 hours, VW-1 for
<br /> 2 hours, and simultaneously on wells MW-1 R, MW-2R, and VW-1 for 92 hours. DPE was
<br /> conducted at vapor extraction flow rates ranging between 10.90 standard cubic feet per
<br /> minute (scfm) to 42.86 scfm, at vacuums ranging from 14 to 25 inches of mercury, and at
<br /> groundwater extraction flow rates ranging from 0.01 gpm to 6.2 gpm. During DPE testing,
<br /> an estimated 8.11 pounds of TPHg, 0.17 pounds of benzene, and 5.26 pounds of MtBE
<br /> were removed from beneath the site, and approximately 26,210 gallons of groundwater
<br /> were extracted and transported off-site for disposal. Based on the results of DPE testing,
<br /> this technology was determined to be ineffective based on the low soil vapor extraction
<br /> radius of influence (24 feet), the large quantity of extracted groundwater, and low estimated
<br /> mass removal quantities (SECOR, 2002).
<br /> SUMMARY OF PREVIOUS INTERIM REMEDIAL ACTION
<br /> Interim remediation via groundwater batch extraction has been performed on a weekly
<br /> basis from wells MW-1R, MW-2R, and VW-1 since August 2000. Between August 2000
<br /> and July 21, 2003, a total of 790,900 gallons of groundwater has been removed from the
<br /> � site. Since January 2, 2002, batch extraction has occurred from well MW-1 R.
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