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i . Mr Ron Rowe Page 2 GROUNDWATER ACTIVITIES Groundwater Monitoring and Sampling Groundwater monitonng was conducted on May 5, 1998 The depth to groundwater was measured in each well and subtracted from the wellhead elevation to determine groundwater elevation Water levels rose an average of 3 03 feet since last monitored on February 25, 1998 Groundwater flow was generally east-southeasterly with a gradient ranging from 0 002 to 0 01 feet per foot A groundwater gradient map generated using the May 5, 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 May 5 and 6, 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 Due to equipment problems, physical parameters (pH, conductivity, temperature) were not monitored during purging Samples were collected after groundwater recharger] to at least 80% 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 l 1, MW 12, and MW13 was delivered by Argon under chain of custody to McCampbell Analytical in Pacheco, California (DHS #f1644) 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 Groundwater Analytical Results Petroleum hydrocarbons were detected in groundwater samples collected from all monitoring wells, except MW7, MW 1 1, and MW 12 Al-hough the TPHg and BTEX concentrations in the sample collected from MW4 showed a decrease since the previous quarter, concentrations were still above historical levels For the second consecutive quarter, concentrations in the sample from MW2 were at levels lower than those shown historically The highest concentrations of TPHg and BTEX were detected in samples collected from wells MW5, MW8, and MW13 Petroleum concentrations are summarized in Table 2 Samples from wells MW 1, MW3, MW4, MW 11, MW 12, and MW13 were also analyzed for oxygenates Oxygenates were not detected in sample from well MW13, although the detection limits were raised as a result of dilution MTBE was detected in samples from wells MW3 and r�rtiamrl2gmI998