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i Mr Ron Rowe 1 Page 2 ' Groundwater flow was generally easterly with a gradient from approximately 0 002 to 0 015 feet g Y Y per foot A groundwater gradient map generated using the November 10, 1998 monitoring data is shown on Figure 2 Recent groundwater monitoring data are summarized in Table 1 Monitoring logs and well construction information are included in Attachment A On November 10 and 11, 1998, Ground Zero collected groundwater samples from groundwater monitoring wells MW 1 through MW 13. 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 Samples were collected after groundwater recharged to 100% of the original level Purged water was ' contained in 55-gallon drums approved by the Department of Transportation and stored onsite in a locked enclosure Purge logs are presented in Attachment A ' Samples were placed on ice and transported under chain of custody to Argon Laboratories (DHS #1873). Samples were analyzed for TPHg using modified EPA method 8015 and BTEX using EPA method 8020 Additional sample matrix collected from monitoring wells MW1, MW3, ' MW4, MW 11, MW12, and MW 13 was delivered by Argon under chain of custody to McCampbell Analytical in Pacheco, California (DHS #1644) and analyzed for oxygenates using modified EPA method 8260 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 Petroleum hydrocarbons were detected in groundwater samples collected from all monitoring wells, except MW6, MW10, MW11, and MW12. Concentrations of TPHg and BTEX in the samples collected from MW 1, MW2, MWS, MW8, MW9, and MW 13 were still within the middle to low historical range. Gasoline hydrocarbons were detected in MW7 for the first time since February, 1997 Hydrocarbon concentrations increased in wells MW3 and MW4 The ' highest concentrations of TPHg and BTEX were detected in samples collected from wells MW4, MWS, MW8, and MW 13 Petroleum concentrations are summanzed in Table 2 ' Samples from wells MW1, MW3, MW4, MW11, MW12, and MW13 were also analyzed for oxygenates Oxygenates were not detected in sample from well MW 13, although the detection limits were rased as a result of dilution MTBE was detected in samples from wells MW3 and tMW4 at concentrations of 220 and 7,000 parts per billion (ppb), respectively DIPE was detected in the samples from wells MW 11 and MW12 at concentrations of 26 and 3 3 ppb, respectively TBA was detected in well MW 1 (64 ppb), MW l l (35 ppb), and well MW12 (45 ' ppb) ETBE and TAME were not detected in any samples The oxygenate concentrations are summarized in Table 3 roWgmM4,n1998