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<br /> S E C ® R
<br /> Smith Canal is located approximately 1,300 feet south of the site, and the Calaveras
<br /> River is located approximately 3,500 feet north of the site Both of these surface water
<br /> bodies are channeled, flow generally to the southwest, and drain into the Stockton Deep
<br /> Water Channel (GRI, Groundwater Monitoring Well, CPT, and Ozone Microsparge
<br /> System Installation Report, May 9, 2003)
<br /> MONITORING AND SAMPLING
<br /> The current monitoring well network consists of 12 wells (MW-1 and MW-3 through MW-
<br /> 13) that are sampled quarterly Groundwater samples were collected by TRC from each
<br /> of the wells on August 26, 2005, except for well MW-8, which was not monitored or
<br /> sampled due to the repaving of the street by the City of Stockton in the area of the well
<br /> The well had been paved over and fresh asphalt was observed to have penetrated the
<br /> cracks of the well lid The well could not be accessed or uncovered as the nearby traffic
<br /> had been diverted over the well
<br /> The groundwater samples were submitted to Severn Trent Laboratories, Inc 's (STL)
<br /> subcontracted laboratory, BC Laboratories, Inc (BC) for analysis of gasoline range
<br /> organics (GRO), BTEX, fuel oxygenates (MtBE, TBA, tertiary amyl methyl ether [TAME],
<br /> DIPE, ethyl tertiary butyl ether [EtBE], ethanol), 1,2-DCA, and ethylene dibromide (EDB)
<br /> by EPA Method 8260B Groundwater samples from wells MW-3 and MW-7 were
<br /> additionally analyzed for acetone, tertiary butyl formate, and tertiary-butyl acetate by
<br /> EPA Method 8260B Results are discussed below and are summarized in TRC's
<br /> Quarterly Monitoring Report, July Through September 2005 dated September 29, 2005
<br /> (Attachment 1)
<br /> Groundwater monitoring and sampling activities at the site were performed in
<br /> conjunction with those performed by Blaine Tech Services (BTS) at the nearby Shell
<br /> Service Station, located at 1267 Country Club Boulevard Groundwater samples were r
<br /> collected by BTS from Shell wells S-1 through S-4 during the third quarter 2005 Shell
<br /> wells S-5 and S-6 are typically sampled annually during the first quarter During the
<br /> August 26, 2005 coordinated sampling event, split samples were collected by TRC from
<br /> Shell wells S-1 through S-4, and access was granted by TRC for sampling off-site Shell
<br /> wells S-5 and S-6 These samples were submitted to STL's subcontracted laboratory,
<br /> BC, for analysis of GRO, BTEX, fuel oxygenates (MtBE, TAME, DIPE, EtBE, TBA, and
<br /> ethanol), 1,2-DCA, and EDB by EPA Method 82608
<br /> DISCUSSION
<br /> During the third quarter 2005, depth to groundwater ranged between 13 77 and 19 25
<br /> feet bgs, which was in range of historical levels Historical groundwater depths have
<br /> been reported between 11 40 feet and 32 14 feet bgs The direction of groundwater flow
<br /> was toward the north at a hydraulic gradient of 0 002 foot per foot (ft/ft), which is also
<br /> consistent with the north to northeast groundwater flow direction reported over previous
<br /> quarters
<br /> The highest concentrations of petroleum hydrocarbons have historically been detected in
<br /> on-site wells MW-3 and MW-7 Concentrations of GRO and benzene were reported at
<br /> • site maximum concentrations of 180,000 pg/L (MW-7) and 472 pg/L (MW-3),
<br /> respectively, during 2001, concentrations within these wells and other on-site wells
<br />
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