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I Mr Ron Rowe Samples from wells MW 1, MW3, MW4, MW7, and MW 11 through MW 13 were also analyzed for oxygenates Oxygenates were not detected, in the samples from wells MW 1, MW7, MW 11, MW 12, and MW 13 MTBE was detected in samples from wells MW3 and MW4 at concentrations of 1,400 and 7,400 parts per billion (ppb), respectively DIPE, TBA, ETBE and TAME were not detected in any of the samples collected from the wells Oxygenate concentrations are summarized in Table 3 Groundwater Sampling Summary and Discussion ' MTBE was detected in well NM for the eighth consecutive quarter MTBE was also detected in well MW3, located downgradient of MW4, for the sixth consecutive quarter, near the highest concentration to date TPHg and BTEX concentrations also remained high in MW3 during this sampling event and increased significantly in MW4 ' Dissolved contaminants present in groundwater from wells MM3, MW4 and MW12 appear to be related in large part, if not entirely, to offsite releases The sudden appearance of MTBE in these wells, the discernable downgradient movement of the MTBE plume and the increased ' concentrations of BTEX — rich gasoline suggests an offsite contributing source It is suspected that the ARCO station at 130 S Wilson Way, the former Top Filling Station at 101 S Wilson Way, or both may the source of this encroaching contamination In addition, we understand that a release of MTBE was recently documented at the ARCO facility This provides further indication that ARCO is the source of the MTBE and fresh gasoline on at least the southern portion of the subject property i VAPOR EXTRACTION SYSTEM ACTIVITIES VES Operation ' The soil vapor extraction system operated on vapor wells VW2, VW5, and VW6 for a total of 1,827 hours between July 1 and September 30, 1999 ' The VES functioned normally during July and most of August The system shut down once in August and twice in September for unknown reasons Ground Zero was able to restart the system each time during regular maintenance and data acquisition inspections The system shut down on August 29, September 15, and on September 22, and was restarted on August 31, September 20, and October 4 1999, respectively during regular monitoring and sampling events The system ' appears to be functioning properly again I During the Third Quarter 1999, the VES was monitored on a weekly basis The systems ' monitoring data sheets are included in Attachment C On July 19, August 23, and September 13, 1999 influent and effluent vapor samples were collected and submitted to Sequoia Analytical or Air Toxics, Ltd for analysis The samples were analyzed for total purgeable petroleum roelc cgw\3gm 1999