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Mr Ron Rowe <br /> Page 2 <br /> shown on Figure 2. Recent groundwater monitoring data are summarized in Table 1 <br /> Monitoring logs are included in Attachment A as is a table of well construction details <br /> From November 18 through 21, 1997, as directed by San Joaquin County Public Health Services <br /> Environmental Health Division (PHSIEHD), Ground Zero collected groundwater samples from <br /> vapor wells VW3, VW4, and VW6 and from groundwater monitoring wells MW 1 through <br /> MW13 Grab samples were collected from vapor wells that contained groundwater At least <br /> three well casing volumes were purged from each groundwater monitoring well prior to <br /> sampling Physical parameters (pH, conductivity, temperature) were monitored during purging <br /> and allowed to stabilize prior to sampling Purged water was contained in 55-gallon drums <br /> approved by the Department of Transportation and remains on site pending analytical results <br /> Purge logs, as wells as well construction details, are presented in Attachment A <br /> i <br /> Samples were placed on ice and transported under chain of custody to Argon Laboratories (DHS <br /> #1873) Samples collected from the monitoring wells were analyzed for TPHg using modified <br /> EPA method 8015 and BTEX using EPA method 8020 Additional sample matrix collected from <br /> monitoring and vapor wells was delivered by Argon under chain of custody to McCampbell <br /> Analytical in Pacheco, California (DHS#1644)and analyzed for oxygenates using modified EPA <br /> method 8250 Recent analytical results of groundwater samples are summarized in Table 2, and <br /> oxygenate results are summarized in Table 3 Attachment B contains laboratory reports and <br /> chain of custody documentation <br /> i <br /> Groundwater Analytical Results <br /> The TPHg and BTEX concentrations in the sample collected from MW4 showed a significant i <br /> increase since the previous quarter Since there was no apparent sample mishandling, the well <br /> was resampled on December 16, 1997 to confirm the hydrocarbon concentrations The field <br /> notes for the resampling are included in Attachment A <br /> Petroleum hydrocarbons were detected in groundwater samples collected from all monitoring <br /> wells, except MW7, MW 11, and MW 12 The highest concentrations of TPHg and BTEX were <br /> detected in samples collected from wells MW2, MW4, MWS, and MW13 The increased <br /> concentrations detected in well MW4 were confirmed by the resampling <br /> Oxygenates (RIPE, ETBE, MTBE, TAME, and TBA) were not detected in samples collected <br /> from monitoring wells MW3, MW6, MW7, and MW13 nor in vapor wells VW3, VW4, and <br /> VW6 However, detection limits were raised for some samples ETBE and TAME were not <br /> detected in any samples However, the detection limits were raised for some samples as a result <br /> of dilution MTBE was only detected in samples from wells MW4 and MW9 at concentrations <br /> of 8,700 ppb and 9 3 ppb respectively The confirmation sampling of MW4 resulted in an <br /> rodclgmrl4ga,i997 <br />