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i <br /> 1 <br /> Mr Ron Rowe <br /> Page 3 <br /> Groundwater Sampling Summary <br /> MTBE was detected in well MW4 for the fifth consecutive quarter, and concentrations increased <br /> significantly from the previous quarter MTBE was also detected in well MW3, located <br /> downgradient of MW4, for the third consecutive quarter (at the highest concentration to date) <br /> Contaminant concentrations present in wells MW4 and MW3 do not appear to be related entirely <br /> to onsite releases due to the presence of MTBE, the period of onsite UST use/removal and the <br /> easterly groundwater flow The sudden appearance of MTBE in these wells in conjunction with <br /> ' increased gasoline concentrations suggests an offsite contributing source It is suspected that the <br /> Top Filling Station at 101 S Wilson Way, the ARCO Station at 130 S Wilson Way, or both <br /> may be the source of this encroaching contamination <br /> tAfter the fifth quarter of oxygenate analysis, the only apparent trends are the presence of MTBE <br /> in wells MW3 and MW4, the presence of DIPE in wells MW 11, and MW 12, and the presence <br /> ' of TBA in wells MW1, MW11, and MW12. The presence or absence of TBA in wells MW3, <br /> MW4 and MW 13 during this sampling round is uncertain due to elevated detection limits <br /> resulting from dilution of these samples ETBE and TAME have not been detected in any <br /> ' samples. <br /> VAPOR EXTRACTION SYSTEM ACTIVITIES <br /> VES Operation <br /> The soil vapor extraction system operated on vapor wells VW2, VW5, and VW6 for a total of <br /> ' 1777 hours between September 14 and December 31, 1998 Following the completion of repairs <br /> in October, the system operated continuously for the balance of the quarter <br /> System failure caused a shutdown on September 14 The nature of the failure was not readily <br /> apparent A manufacturers representative determined that the internal logic system was <br /> corrupted The system was reprogrammed on October 8 However, memory could not be <br /> ' retained by the controller The digital recorder/controller was removed and shipped to the <br /> manufacturer for repair On October 14 the recorder/controller was reinstalled and the logic <br /> system reprogrammed Startup was successful The system subsequently was down from <br /> ' October 15 through 19 due to a plastic bag clogging the supplemental air flow blower The <br /> system was restarted on October 19 and operated continuously through December 31 <br /> ' During the fourth quarter 1998, the VES was monitored on a weekly basis The systems <br /> monitoring data sheets are included in Attachment C On October 26, November 23, and <br /> ' December 21, 1998 influent and effluent vapor samples were collected Additional influent <br /> samples were collected on December 7, 1998 and submitted to Sequoia Analytical for analysis <br /> in order to confirm the significant decrease in influent concentrations reported for the November <br /> ' 23 sampling event The samples were analyzed for TPPH and BTEX <br /> i <br /> I <br />