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' Mr Ron Rowe Page 3 Samples from wells MW 1, MW3, MW4, MW I I, MW12, and MW 13 were also analyzed for ' oxygenates Oxygenates were not detected in the sample from well MW 13, although the detection limits were raised as a result of dilution MTBE was detected in samples from wells MW3 and MW4 at concentrations of 1,600 and 1,700 parts per billion (ppb), respectively MTBE was also ' detected in well MW12 for the first time at a concentration of 12 ppb DIPE was detected in the samples from wells MW11 and MW12 at concentrations of 22 and 2 7 ppb, respectively TBA ' was detected in well MW 1 (310 ppb), MW 11 (18 ppb), and well MW12 (18 ppb) ETBE and TAME were not detected in any samples Oxygenate concentrations are summarized in Table 3 ' Groundwater Sampling Summary and Discussion MTBE was detected in well MW4 for the sixth consecutive quarter MTBE was also detected m well MW3, located downgradient of MW4, for the fourth consecutive quarter at the highest ' concentration to date TPI-Ig and BTEX concentrations also increased an order of magnitude in MW3 during this sampling event In addition, MTBE was detected for the first time in well MW12, located downgradient of MW3 ' Dissolved contaminants present in groundwater from wells MW3, MW4 and MW12 appear to be related in large part 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 the southern portion of the subject property After the sixth quarter of oxygenate analysis, the only apparent trends are the presence of MTBE in ' wells MW3, MW4, and for the first time in MW12, the presence of DIPE in wells MW 11 and MW12, and the presence of TBA in wells MW 1, MW 11, and MW12 The presence or absence of TBA in wells MW3, MW4 and MW13 is uncertain due to elevated detection limits resulting from ' dilution of these samples ETBE and TAME have not been detected in any samples VAPOR EXTRACTION SYSTEM ACTIVITIES ' VES Operation The soil vapor extraction system operated on vapor wells VW2, VW5, and VW6 for a total of ' 1268 hours between January 1, 1999 and March 31, 1999 -k%q=k1gm 1499 1