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S EC ® R
<br /> Mr Michael Infurna—SJCEHD
<br /> January 29, 2003
<br /> Page 5
<br /> samples were collected directly from a spigot at the holding tank DW-2R, DW-3, and DW-4 are t
<br /> sampled quarterly, and DW-1 is sampled monthly f
<br /> Groundwater Sampling Procedures
<br /> The groundwater monitoring wells were re-monitored to verify at least 80% recovery prior to
<br /> sampling Adequate recovery was observed in the purged wells prior to sampling A disposable
<br /> bailer was used to collect the groundwater samples All samples were collected in appropriate
<br /> containers, preserved on ice, and transported under chain-of-custody manifest to Kiff Analytical LLC
<br /> located in Davis, California
<br /> The water samples were analyzed for TPHg, BTEX, 1,2-DCA, EDB, and five oxygenates using EPA
<br /> method 8260B Per the RWQCB written request, the water samples collected from wells MW-5,
<br /> MW-5D, MW-6, and MW-9 were also analyzed for dissolved metals using EPA Method 200 8
<br /> Groundwater Analytical Results
<br /> Historical and recent groundwater laboratory analytical results are summarized in Table 3 The
<br /> highest benzene and TPHg concentrations were detected in MW-3 at 7,000 ppb and 93,000 ppb,
<br /> respectively (Figure 5) The highest MtBE concentration was detected in monitoring well MW-1 at
<br /> and 250 ppb Other oxygenates were not detected above the laboratory reporting limits in samples
<br /> collected from the monitoring wells Well AS-1, located within the source area and screened from 40 ;
<br /> to 45 feet bgs, was sampled for the second time The water sample did not contain concentration of
<br /> TPHg, BTEX or oxygenates above the laboratory reporting limits (Table 3) The dissolved metal
<br /> concentrations from wells MW-5, MW-5D, MW-6, MW-7 and MW-9 will be compared with future l
<br /> dissolved metal concentrations in order to monitor the effects of the ozone sparge remedial system
<br /> (Table 4)
<br /> Domestic Well Analytical Results
<br /> 3
<br /> The water samples collected from domestic wells DW-2R, DW-3, and DW-4 sampled quarterly did
<br /> not contain detectable concentrations of TPHg, BTEX, oxygenates, 1,2-DCA, or EDB DW-1,
<br /> sampled on November 4, 2002, contained detectable concentrations of toluene, xylenes, and TBA at
<br /> concentrations of 1 4 ppb, 0 63 ppb, and 5 8 ppb, respectively DW-1 was resampled on November
<br /> 15 and December 11, 2002 and all concentrations were reported as nondetect Copies of the
<br /> laboratory analytical reports and chain-of-custody manifests are included in Attachment 4
<br /> Conclusions
<br /> Nine of the ten groundwater monitoring wells, one air sparge well, and four domestic water wells
<br /> were sampled this quarter Well MW-7 was not sampled due to access limitations Groundwater
<br /> elevation decreased an average 0 42 feet since July 2002 Referring to Table 3, an increase in the
<br /> concentration of benzene, TPHg, and MtBE was observed in well MW-4 Perimeter wells MW-6,
<br /> MW-8, and MW-9, and the source area AS-1 screened approximately 10 feet below the water table
<br /> from 40 to 45 feet bgs did not contain benzene, TPHg, or MtBE above laboratory reporting limits this
<br /> quarter It appears the dissolved petroleum hydrocarbons in the source area are present within the
<br /> upper 10 feet of the saturated zone and are laterally defined by perimeter wells MW-6, MW-8, and
<br /> MW-9
<br /> Riverbank-02-40 doc SECOR international Incorporated
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