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I <br /> Mr Ron Rowe <br /> Page 3 of 6 <br /> MW13 MTBE was detected in samples from wells MW3 and MW4 at concentrations of 1,400 <br /> and 3,400 parts per billion (ppb), respectively DIPE was detected in the sample from well <br /> MW11 at a concentration of 16 ppb TBA, ETBE and TAME were not detected in any samples <br /> Oxygenate concentrations are summarized in Table 3 <br /> Groundwater Sampling Summary and Discussion <br /> 1 MTBE was detected in well MW4 for the seventh consecutive quarter MTBE was also detected <br /> in well MW3, located downgradient of MW4, for the fifth consecutive quarter near the highest <br /> concentration to date TPHg and BTEX concentrations also remained high in MW3 and MW4 <br /> ' during this sampling event <br /> ' Dissolved contaminants present in groundwater from wells MW3, MW4 and MW 12 appear to be <br /> t, related in large part to offsite releases The sudden appearance of MTBE in these wells, the <br /> discernable downgradient movement of the MTBE plume and the increased concentrations of <br /> BTEX — rich gasoline suggests an offsite contributing source It is suspected that the ARCO <br /> station at 130 S Wilson Way, the former Top Filling Station at 101 S Wilson Way, or both may <br /> the source of this encroaching contamination In addition, we understand that a release of MTBE <br /> was recently documented at the ARCO facility <br /> After the eigth quarter of oxygenate analysis, the only apparent trends are the presence of MTBE <br /> in wells MW3, MW4 ETBE, TAME and TBA were not been detected in any samples this <br /> quarter, and ETBE and TAME have never been detected in groundwater at the site <br /> VAPOR EXTRACTION SYSTEM ACTIVITIES <br /> u <br /> VES Operation <br /> The soil vapor extraction system operated on vapor wells VW2, VW5, and VW6 for a total of <br /> 1,914 hours between April 1, 1999 and June 30, 1999 <br /> The VES was shut down from April 8 through April 13 due to burned out motor New <br /> components were installed and the system was restarted and placed back in full time operation on <br /> on April 13, 1999 The system functioned properly during the months of May and June <br /> During the second quarter 1999, the VES was monitored on a weekly basis (except during system <br /> shutdown) The systems monitoring data sheets are included in Attachment C On April 19, and <br /> May 24, June 14, and June 21, 1999 influent and effluent vapor samples were collected and <br /> I1 subnutted to Sequoia Analytical for analysis The samples were analyzed for total purgeable <br /> L petroleum hydrocarbons (TPPH) and BTEX <br /> rock*nr\2"19" <br /> v <br /> r <br />