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' Fourth Quarter 2004 Groundwater Report
<br /> 8200 N Highway 99, Stockton, CA
<br /> Page 3 of 6
<br />' calculated to be 36 87 and 37 01 feet below MSL, respectively, an average rise of 2 40 feet between
<br /> September 14, 2004 and December 14, 2004 The groundwater elevation in C Zone well MW 13C
<br /> was measured at 69 77 feet btoc (37 59 feet below MSL), a rise of 3 23 feet between September 14,
<br />' 2004 and December 14, 2004
<br /> Groundwater in the A Zone aquifer on December 14, 2004 generally flowed in a northeasterly
<br />' direction, although a cone of depression is evident around both of the extraction wells The
<br /> groundwater gradient across the site was 0 002 on December 14, 2004, or approximately 10 feet
<br /> per mile Table 4 summarizes groundwater elevations in site monitoring wells Figure 3
<br />' presents a potentiometric surface map generated using the December 14, 2004 monitoring data
<br /> Attachment C contains field notes
<br />' 3.2 Groundwater Sampling and Analysis
<br /> An experienced Ground Zero technician purged at least three well casing volumes of water from
<br />' monitoring wells MW2 through M W 16 prior to sampling The vapor extraction well V W 1 went
<br /> dry after only 1 8 casing volumes was produced The technician measured the temperature, pH
<br /> and electrical conductivity of the water during the purging process Purged groundwater was
<br />' contained in appropriately labeled DOT-approved 55-gallon drums in accordance with 49 CFR
<br /> part 172 and 40 CFR part 262, and will eventually be processed through the groundwater
<br /> treatment system Attachment C contains field purge logs
<br /> Groundwater samples were collected after the physical parameters stabilized and water levels in
<br /> the wells recovered to at least 95% of their respective pre-purged levels Groundwater samples
<br /> were also collected from the extraction wells EWI (MW1) and EW2 The samples were
<br /> temporarily stored in an ice chest refrigerated to a temperature of approximately 4°C and
<br /> delivered under chain of custody protocol to Argon Laboratories (ELAP #2359) for analysis
<br /> Argon Laboratories analyzed all groundwater samples collected for total petroleum hydrocarbons
<br /> as gasoline (TPHg) using EPA 801513, benzene, toluene, ethylbenzene, and total xylenes (BTEX)
<br /> I using EPA 8021B, and oxygenated gasoline additives, ethylene dibromide (EDS), 1,2-
<br /> dichloroethane (1,2-DCA)using EPA 8260B
<br /> I No gasoline constituents, including MTBE, were detected in the groundwater samples collected
<br /> from shallow aquifer wells MW7, MWS, MW10, MW11, MW15 or MW16 in December 2004 In
<br /> addition, no gasoline constituents or MTBE were detected in deeper zone wells MW9B or
<br /> MW 14B
<br /> TPHg. and BTEX constituents were detected in groundwater samples collected from wells EW1,
<br /> MW2 and VW1 in December 2004 The sample collected from well EW1 contained TPHg at
<br /> 6,200 parts per billion (ppb), benzene at 890 ppb, toluene at 1,200 ppb, ethylbenzene at 27 ppb, and
<br /> xylenes at 540 ppb Well EW1 was also sampled this quarter on October 26 and November 24,
<br /> 2004 The results for those sampling events are given on Table 5 Well MW2 contained TPHg at
<br /> 210 ppb, benzene at 3 1 ppb, ethylbenzene at 2 2 ppb, and xylenes at 4 1 ppb Well V W 1 contained
<br /> TPHg at 10,000 ppb, benzene at 1,200 ppb, toluene at 720 ppb, ethylbenzene at 380 ppb, and
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