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S E C 0 R
<br /> 2001}
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<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 dram 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 — SECOND QUARTER 2005
<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 W
<br /> well on May 27, 2005, and were submitted to Severn Trent Laboratories, Incorporated
<br /> (STL) for analysis of gasoline range organics (GRO), BTEX, fuel oxygenates (MtBE,
<br /> TBA, tertiary amyl methyl ether ]TAME], DIPE, ethyl tertiary butyl ether [EtBE], ethanol),
<br /> 1,2-DCA, and ethylene dibromide (EDB) by EPA Method 82608 Groundwater samples
<br /> from wells MW-3 and MW-7 were additionally analyzed for acetone by EPA Method
<br /> 82606 Results are discussed below and are summarized in TRC's Quarterly Monitoring
<br /> Report, April Through June 2005 dated June 28, 2005 (Attachment 1)
<br /> Groundwater monitoring and sampling activities at the site are typically performed in
<br /> conjunction with those performed concurrently at the nearby Shell Service Station,
<br /> located at 1267 Country Club Boulevard, however, during the second quarter 2005,
<br /> Blaine Tech Services (BTS) performed groundwater monitoring and sampling at the
<br /> Shell Service Station one week prior to the TRC sampling event on May 20, 2005
<br /> Groundwater samples are collected by BTS from Shell wells S-1 through S-4 quarterly,
<br /> and from Shell wells S-5 and S-6 annually during the first quarter Groundwater
<br /> samples were submitted by BTS for analysis of GRO, BTEX, and 1,2-DCA by EPA
<br /> Method 8260B, and TPHd by EPA Method 8015M Upon authorization granted by
<br /> representatives of the Shell Service Station, TRC requested that STL report the
<br /> analytical results for wells S-1 through S-4 for fuel oxygenates g (MtBE, TAME, DIPS,
<br /> EtBE, TBA, and ethanol), 1,2-DCA, and EDB by EPA Method 8260B These results are
<br /> included in Attachment 1 The EDB results for wells S-2 and S-4, however, were not r„
<br /> reported, as the equipment was not calibrated to run EDB on the day that the samples
<br /> were analyzed 3
<br /> DISCUSSION
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<br /> During the second quarter 2005, depth to groundwater ranged between 12 01 and 16 73
<br /> feet bgs, which was in range of historical levels Historical groundwater depths have 3
<br /> been reported between 11 40 feet and 32 14 feet bgs The direction of groundwater flow
<br /> was toward the northeast at a hydraulic gradient of 0 002 feet per toot (ft/ft), which Is
<br /> also consistent with the groundwater flow direction reported over previous quarters
<br /> (north and northeast)
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<br /> The highest concentrations of petroleum hydrocarbons have historically been detected in E
<br /> on-site wells MW-3 and MW-7 within concentrations of GRO and benzene peaking In ,
<br /> 2001 at site maximum concentrations of 180,000 pg/L (MW-7) and 472 pg/L (MW-3),
<br /> respectively, concentrations within these wells and other on-site wells MW-1, MW-3,
<br /> MW4, and MW-6 have since declined over time Petroleum hydrocarbon
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