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Mr Ron Rowe <br /> Page 3 of 5 <br /> ' MW7 following three consecutive rounds of non-detectable or trace concentrations MTBE was <br /> also present in MW7, for the first time Wells MW3 and MW4 are located along the southern <br /> ' boundary of the subject property and are affected by offsite releases MW7, located slightly north <br /> of MW3, is now apparently affected as well TPHg and BTEX concentrations are summarized in <br /> Table 2 <br /> ' Samples from all wells were also analyzed for oxygenates Oxygenates were not detected in the <br /> samples from wells MW1, MW2, MWS, MWb, MW8, MW10, MWII, MW12, and MW13 <br /> ' MTBE was detected in samples from wells MW3 and MW4 at concentrations of 1,500 and 4,000 <br /> parts per billion (ppb), respectively and in samples from MW7 and MW9 at levels of 12 and 18 <br /> ppb, respectively The source of MTBE in each of these wells is believed to be offsite releases <br /> DIPE, TBA, ETBE and TAME were not detected in any of the samples collected from the wells <br /> Oxygenate concentrations are summarized in Table 3 <br /> ' Groundwater Sampling Summary and Discussion <br /> MTBE was detected in well MW4 for the ninth consecutive quarter MTBE was also detected in <br /> ' well MM3, located downgradient of MW4, for the seventh consecutive quarter, near the highest <br /> concentration to date TPHg and BTEX concentrations also remained high in MW3 during this <br /> sampling event and increased significantly in MW4 TPHg, BTEX and MTBE were detected in <br /> MW7, located north of well MW3 <br /> Dissolved contaminants present in groundwater from wells MW3, MW4 and MW7 appear to be <br /> related in large part, if not entirely, to offsite releases The sudden appearance of MTBE in these <br /> wells, the discernable downgradient movement of the MTBE plume and the increased <br /> ' concentrations of BTEX — rich gasoline suggests an offsite contributing source It is suspected <br /> that the ARCO station at 130 S Wilson Way, the former Top Pilling Station at 101 S Wilson <br /> Way, or both may the source of this encroaching contamination In addition, we understand that <br /> a release of MTBE was recently documented at the ARCO facility This provides further <br /> indication that ARCO is the source of the MTBE and fresh gasoline on at Ieast the southern <br /> portion of the subject property <br /> ' Hydrocarbon concentrations in well downgradient of the former onsite USTs continue to decline <br /> in wells MW2, MW8 and MW13 Concentrations in well MW5 are stable Overall, the plume of <br /> contamination is diminishing <br /> 1 <br /> roek%gmrl4gm 1999 <br />