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i I ' Mr. Ron Rowe Page 2 shown on Figure 2. Recent groundwater monitoring data are summarized in Table I Monitoring logs and well construction information are included in Attachment A On August 11 and 12, 1998, Ground Zero collected groundwater samples from groundwater monitoring wells MW 1 through MW13. 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 1 l, MW 12, and MW13 was delivered by Argon under chain of custody to McCampbell Analytical in Pacheco, California (DHS #1644) and analyzed for oxygenates using t 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 Groundwater Analytical Results Petroleum hydrocarbons were detected in groundwater samples collected from all monitoring ' wells, except MW7, MW 10, MW 11, and MW 12 Although the TPHg and BTEX concentrations in the samples collected from MW 1, MW2, MW5, MW6, and MW9 showed a decrease since the previous quarter, concentrations were still within the middle to low historical range The ' highest concentrations of TPHg and BTEX were detected in samples collected from wells MW4, MW5, MW8, and MW13 Petroleum hydrocarbon concentrations are summarized in Table 2 ' Samples from wells MW 1, MW3, MW4, MW 11, MW 12, and MW 13 were also analyzed for oxygenates Oxygenates were not detected in the sample from well MW13, although the detection limits were raised as a result of dilution MTBE was detected in samples from wells ' MW3 and MW4 at concentrations of 27 and 600 parts per billion (ppb), respectively DIPE was detected in the samples from wells MW4 (1 6 ppb), MW11 (28 ppb), and MW12 (3 4 ppb) TBA was detected in all the samples, except from MW13, at concentrations ranging from 26 to ' 130 ppb ETBE and TAME were not detected in any samples The oxygenate concentrations are summarized in Table 3 ' Groundwater Sampling Summary MTBE was detected in well MW4 for the fourth consecutive quarter, and concentrations ' increased from the previous quarter's historic low MTBE was also detected in well MW3, meklgmrl3gmS998 doc