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S E C 0 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 Wells MW-1, MW-3 through MW-10, MW-12, and MW-
<br /> 13 are screened in the shallow water-bearing zone, and well MW-11 is screened in the
<br /> intermediate water-bearing zone Groundwater samples were collected by TRC from
<br /> each of the wells on November 11, 2005
<br /> The groundwater samples were submitted to Severn Trent Laboratories, Inc (STL) for
<br /> analysis of gasoline range organics (GRO), BTEX, fuel oxygenates (MtBE, TBA, tertiary
<br /> amyl methyl ether (TAME], DIPE, ethyl tertiary butyl ether [EtBE], and ethanol), 1,2-DCA,
<br /> and ethylene dibromfde (EDB) by EPA Method 8260B Groundwater samples from wells
<br /> MW-3 and MW-7 were additionally analyzed for acetone by EPA Method 82608 Due to
<br /> a laboratory oversight, the groundwater samples from wells MW-3 and MW-7 were not
<br /> analyzed for tertiary butyl formate and tertiary butyl acetate by EPA Method 8260B
<br /> Results are discussed below and are summarized in TRC's Quarterly Monitoring Report,
<br /> October Through December 2005 dated December 27, 2005 (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 During the November 11,
<br /> 2005 coordinated sampling event, split samples were collected by TRC from Shell wells
<br /> S-1 through S-4, and TRC obtained permission to sample off-site Shell wells S-5 and S-
<br /> 6 These samples were submitted to STL for analysis of GRO, BTEX, fuel oxygenates
<br /> (MtBE, TAME, DIPE, EtBE, TBA, and ethanol), 1,2-DCA, and EDB by EPA Method
<br /> 8260B
<br /> DISCUSSION
<br /> During the fourth quarter 2005, depth to groundwater ranged between 14 63 and 19 21
<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 /> MW-1, MW-4, and MW-6 have since declined over time Petroleum hydrocarbon
<br /> concentrations have generally not been detected at or above laboratory MRLs in wells
<br /> MW-5, and MW-8 through MW-10, MW-12, and MW-13 Well MW-11, which is
<br /> • screened in a deeper water-bearing zone beneath the site, has occasionally contained
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