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1 <br /> EIN Wt <br /> Ms. Margaret Lagorio <br /> ' May 4, 2005 <br /> Page 4 <br /> ' Periodic groundwater samples are collected from wells U-3, U-10 and peizometers NP-1 and <br /> NP-2 to further assess the effectiveness of the Ozone Microsparge system. Such groundwater <br /> 1 samples were collected at the site on January 28, 2005 and were submitted to CLS for analyses <br /> of BTEX by EPA Method 8021 and TPHg by EPA Method 8015 Modified. Laboratory analytical <br /> results with chain-of-custody documentation are included in Attachment C. Cumulative <br /> 1 groundwater sampling analytical results for wells U-3 and U-10 and piezometers NP-1 and NP-2 <br /> are summarized in Table 9. Graphs of concentrations of TPHg and benzene versus time in wells <br /> U-3 and U-10 and piezometers NP-1 and NP-2 are included as Attachment D. <br /> 1 Based on a the concentrations of dissolved TPHg and benzene in zone A wells U-1 through <br /> U-6, U-7, and U-8, in zone B wells U-13, U-14, U-20, and piezometer NP-1-65 and NP-2-60, <br /> and zone C wells U-10, U-12, U-17, U-21 and piezometer NP-2-116 during first quarter 2005, <br /> 1 the C-SpargeTM system appears to have reached its maximum potential to remediate all zones <br /> and constituents of concern beneath the site. <br /> 1 Discussion <br /> Groundwater analytical results for wells U-1 through U-6, U-7, U-8, U-10, U-12 through U-14, <br /> 1• U-17, U-20, U-21, NP-1-65, NP-2-60, and NP-2-116 indicate that the C-SpargeTM system <br /> appears to be effective at decreasing concentrations of dissolved TPHg and benzene in zone A, <br /> zone B and zone C beneath the site. <br /> 1 The groundwater gradients appear similar to previous quarters. Average groundwater <br /> elevations have deceased approximately 0.50 feet since November 2004. <br /> 1 MTBE was not detected at or above the laboratory reporting limit in any of the monitoring wells <br /> during the first quarter 2005 groundwater monitoring and sampling event. <br /> ' Concentrations of TPHg were not reported at or above the laboratory detection limits in wells U4 <br /> through U-9, U-14, and U-15, during the eight most recent quarterly sampling events. <br /> 1 Except for well NP-2-22, concentrations of MTBE were not reported at or above the laboratory <br /> detection limits in the remaining site wells during the five most recent quarterly sampling events. <br /> 1 Recommendations <br /> ENSR recommends that the C-SpargeT"" system be re-evaluated to assess the system's ability <br /> ' to remediate the A-, B- and C-water bearing zones and constituents of concern beneath the site. <br /> ENSR recommends that the Monitoring and Reporting Program be modified and that the <br /> laboratory analyses for TPHg in groundwater samples collected from wells U4 through U-9 (zone <br /> ' A), U-14 (zone B), and U-15 (zone C) be discontinued. Additionally, with the exception of wells <br /> • U-18 (zone B), U-26 (zone C), and NP-2-22 (zone A), ENSR recommends that the analyses for <br /> ' J:Trojects10694010187-3251WorkingkReports101871 st Qtr 05-QMR RSR.doc <br /> Celebrating 35 Years of Excellence in Environmental Services <br />