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1 Ms Margaret Lag ono Page 3 of 5 � Vapor Extraction Wells 1 The concentrations of TPHg and benzene reported in vapor wells VW1, VW2, VW4 and VWS remained relatively stable since the last event In vapor well VW6, TPHg decreased to near the historic low while ' the level of benzene decreased over one order of magnitude to the lowest level recorded No gasoline oxygenate additives, EDB, 1,2-DCA were detected in any sampled vapor wells, except VW4 1,2 DCA was detected in well VW4 at a concentration of 110 ppb TPHg and BTEX concentrations are ' summarized in Table 2 1,2-DCA, EDB and gasoline oxygenate additive concentrations are summarized in Table 3 Attachment B contains laboratory reports and chain of custody documentation ' GROUNDWATER SAMPLING SUMMARY AND DISCUSSION ' • Water levels fell during this quarter Groundwater elevation data continue to show an easterly groundwater flow direction ' • Despite variability from sampling event to sampling event, the extent of groundwater contamination associated with the onsite release is stable and concentrations are stable to decreasing ' • High levels of MTBE persist in the wells located along the southern portion of the property The concentrations in wells MW3, MW4, and MW14 are at the highest levels to date The contamination ' plume originating at the Top Filling Station is continuing to spread and is now comnungling: with the Knowles Plume VAPOR EXTRACTION SYSTEM ACTIVITIES ' Vapor Extraction System Operation As requested by EHD, the soil vapor extraction was operated on an intermittent basis during the first/second quarters of 2002 to evaluate current hydrocarbon removal capabilities On March 7, 2002, the San Joaquin Valley Air Pollution Control District (APCD) inspected the vapor extraction system (VES) ' During the inspection vapor samples were collected from the influent and effluent to determune the destruction efficiency Analysis consisted of TPHg, BTEX and MTBE using EPA Method TO-3 The system was subsequently shut down pending analytical results Analytical results indicated a destruction ' efficiency of greater than 99 % On March 18, 2002, the VES was restarted The system was operated intermittently from March 18 ' through June 17, 2002 In general, the system was operated for a period of a week or more, shut down for a similar period and then restarted Field notes are included in Attachment D During each period of operation, influent samples were collected after startup and before shutdown in order to bracket the ' concentration decline during operation and the increase after operational hiatus Effluent samples were collected on a monthly basis as per APCD requirements Samples were submitted to state-certified Air Toxics Laboratories for the analysis of TPHg, BTEX and MTBE by EPA Method TO-3 Analytical data ' roeklgnuMgm2002