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880 Victor Road,Lodi <br /> Former Shell Service Station <br /> Page 3 <br /> In a letter dated July 22,2002,you were directed to conduct a full 8260B scan and report all <br /> peaks for one quarter sampling event annually to monitor for degradation products of <br /> oxygenate compounds. Since TBA concentrations in the wells have continued to rise as <br /> MTBE concentrations fall, there is strong evidence that degradation of MTBE to other <br /> oxygenate compounds are occurring at the site. This annual full scan has not been <br /> conducted to date. <br /> In Response Letter/Site Investigation and ThirdQuarter 2002 Groundwater Monitoring Dort/Work <br /> Plan dated December 13,2002,your consultant, Cambria,responded to EHD directive that <br /> you and Cambria are in the process of discussing this request with the CVRWQCB. This <br /> directive was included in the July 2002 EHD letter after discussion with Central Valley <br /> Regional Water Quality Control Board (CVRWQCB) staff. In a meeting with on March 12, <br /> 2003,CVRWQCB again supported the EHD directive to conduct a full 8260B scan.. EHD <br /> requests you to conduct a full 8260B scan and report all peaks for the 2nd quarterly <br /> monitoring event of 2003. <br /> EHD is concerned with the potential hydrolysis of MTBE to TBA and methanol in <br /> groundwater samples and the accuracy of the reported concentrations.Acidity is one of the <br /> more important factors that influence the rate of hydrolysis of MTBE. For each drop in pH <br /> of one unit, the rate of reaction increases 10 times. In normal groundwater sample <br /> collecting procedure hydrochloric acid is added to sample vials to bring the sample pH to <2 <br /> as a preservative against bio-degradation of the hydrocarbon content in the samples. <br /> However,this lowering of the pH may increase the hydrolysis of MTBE such that the <br /> analytical results may under-estimate the actual concentrations of MTBE and over-estimate <br /> the concentrations of TBA. EHD recommends collecting split samples for at least two <br /> quarters,with one group using an acidic preservative, and the other using a base, trisodium <br /> phosphate (TSP) to evaluate the effect of pH on MTBE and TBA concentrations. <br /> Donna Heran,REHS,Director <br /> Environmental Health Department <br /> Jeffrey ong, enior REHS Nuel C. Henderson,Jr.,RG <br /> LOP/Site Mitigation Unit IV LOP/Site Mitigation Unit IV <br /> C: CRWQCB,Central Valley Region—James L. L. Barton,RG <br /> C: Cambria Environmental Technologies,Inc.—Aubrey Cool <br />