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1 EFLIt. <br /> 1 <br /> Ms. Margaret Lagorio <br /> ' February 11, 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. The periodic <br /> 1 groundwater samples were submitted to CLS for analyses of BTEX by EPA Method 8021 and <br /> TPHg by EPA Method 8015 Modified. Laboratory analytical results with chain-of-custody <br /> documentation are included as Attachment C. Cumulative groundwater sampling analytical <br /> results for wells U-3 and U-10 and piezometers NP-1 and NP-2 are summarized in Table 9. <br /> 1 Graphs of concentrations of TPHg and benzene versus time in wells U-3 and U-10 and <br /> piezometers NP-1 and NP-2 are included as Attachment D. <br /> ' Based on a the concentrations of dissolved TPHg and benzene in zone A wells (U-1 through U- <br /> 6, U-7, and U-8), zone B wells (U-13, U-14, and U-20), and peizometer wells (NP-1-65, NP-2- <br /> 60), and zone C wells (U-10, U-12, U-17, U-21) and peizometer (NP-2-116) during fourth <br /> quarter 2004, the C-SpargeM system appears to have reached its maximum potential to <br /> remediate all zones 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 /> U-17, U-20, U-21, NP-1-65, NP-2-60, and NP-2-116 indicate that the C-Sparge system <br /> ' • <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 /> ' The groundwater gradients appear similar to previous quarters. Groundwater elevation <br /> deceased approximately 0.50 feet since August 2004. <br /> ' MTBE was not detected at or above the laboratory reporting limit in any of the monitoring wells <br /> during the fourth quarter 2004 groundwater monitoring and sampling event. <br /> Concentrations of TPHg were not reported at or above the laboratory detection limits in wells U-4 <br /> through U-9, U-14, and U-15, during the eight most recent quarterly sampling events. <br /> 1 Except for wells U-18, U-26 and NP-2-22, concentrations of MTBE were not reported at or above <br /> the laboratory detection limits in the remaining site wells during the five most recent quarterly <br /> sampling events. <br /> 1 Recommendations <br /> ENSR recommends that the C-SpargeTM system be re-evaluated to assess the system's ability <br /> 1 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 /> 1 laboratory analyses for TPHg in groundwater samples collected from wells U-4 through U-9, U-14, <br /> and U-15 be discontinued. Additionally, with the exception of wells U-18, U-26 and NP-2-22, the <br /> • <br /> 1 J:Trojects10694010187-3251Working'Reports10187 4th Qtr 04-QMR RSR.doc <br /> ' Celebrating 35 Years of Excellence in Environmental Services <br />