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E�® Mr James L Barton April 12, 2005 Page 6 EMTBE was detected in MW-25S (0 77 pg/L) during the first quarter 2005 groundwater monitoring and sampling event MTBE was not found in samples from any other well in the first quarter 2005 sampling event In response to the RWQCB letter dated February 23, 2004, ENSR is preparing a workplan for the installation of one additional air sparging well and the conversion of a monitoring well into an air sparging well The work plan is being prepared for submittal prior to March 31, 2005 A copy of the RWQCB letter dated February 23, 2004 is included as Attachment H Recommendations Since the fourth quarter 2003, ENSR has observed stable to decreasing trends of dissolved TPHg and benzene concentrations in groundwater samples collected from monitoring wells located within the site boundaries Based on the stable to decreasing trends in wells located onsite, ENSR recommends that during the second quarter of 2005, the SVE and AS systems operate continuously and be monitored on a weekly basis to maximize contaminant removal and minimize downtime ENSR also recommends that quarterly groundwater monitoring continue IFuture Work ENSR will continue to optimize the AS system in order to limit system downtime and increase the effectiveness of the system ENSR will submit a work plan to expand the air sparging remediation system by installing one additional sparging well in the vicinity of MW-3 and by modifying MW-23S into a sparging well Both wells are screened in water bearing zone `C' and are intended to remediate concentrations of dissolved hydrocarbons in the shallower `B' zone The second quarter 2005 groundwater monitoring and sampling is scheduled for April 2005 i i J 1Proiects10694015098-2931WorkinglReports15098 tst Qtr 05-QMR doc r Celebrating 3�i Years of Excellence m Environmental Services