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Margaret Lagorio <br /> April 26, 2004 <br /> Page 4 <br /> ' Benzene Concentration Trends <br /> • Benzene concentrations decreased in piezometers NP-1-22, NP-2-116 since the last <br /> sampling event. <br /> Benzene concentrations in well U-3, and piezometers NP-1-65 and NP-2-60 increased since <br /> the last sampling event. <br /> ' Benzene concentrations remained below laboratory reporting limits in monitoring well U-10 <br /> and piezometers NP-1-111 and NP-2-22. <br /> MtBE Concentration <br /> ' MtBE was detected in piezometer NP-2-22 at 1.4 µg/L. All remaining well samples were <br /> below laboratory reporting limits. <br /> Discussion <br /> ' During March 2004, new tubing, valves and fittings were installed on the <br /> 9 g existing system. <br /> Concentrations of petroleum hydrocarbons in groundwater are expected to decrease near wells <br /> U-3, U-10, NP-1-22, NP-1-65 and NP-2-22 due to system upgrades. <br /> Recommendations <br /> ENSR recommends that operation of the Ozone Pilot Test continue and further groundwater <br /> sampling and D.O. monitoring be performed to evaluate the system's effectiveness. <br /> Future Work <br /> The second quarter groundwater monitoring and sampling is currently scheduled for May 2004. <br /> Remarks/Signatures <br /> ' The interpretations in this report represent our professional opinions and are based, in part, on <br /> the information supplied by the client. These opinions are based on currently available <br /> information and are arrived at in accordance with currently accepted hydrogeologic and <br /> ' engineering practices at this time and location. Other than this, no warranty is implied or <br /> intended. <br /> J:1Projects10694010187-3251FinallReportsllst Qtr 04-QMR RSR10187 1st Qtr o4-QMR RSR.doc <br /> ' ✓ 35 Years of Excellence in Environmental Services <br />