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