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T1 Groundwater Monitoring to and Analytical Results Former Tosco(Unocal)Service Station#4409 1502 North El Dorado Street - Stockton,California EXPLANATION'S TOC=Top of Casing TPH-G=Total Petroleum Hydrocarbons as Gasoline (ppb)=Parts per billion (ft)=Feet B=Benzene ND=Not Detected DTW=Depth to Water T=Toluene --=Not Measured/Not Analyzed S I =Screen Interval E=Ethylbenzene QA=Quality Assurance/Trip Blank (ft bgs)=Feet Below Ground Surface X=Xylenes GW E=Groundwater Elevation MTBE=Methyl tertiary butyl ether (msi)=Mean sea level D Lead=Dissolved Lead TOC elevations were re-surveyed in November of 2001,by Stegfned Engineering,using the previous benchmark Previously,TOC elevations were surveyed relative to msi, per the City of Stockton Benchmark No 23,(Elevation= 11 14 feet,msl)NGVD 29 1 MTBE by EPA Method 8260 '- Laboratory report indicates gasoline C6-C12 3 Laboratory report indicates weathered gasoline C6-C12 ° Well development performed 5 Detection limit raised Refer to analytical reports 6 Laboratory report indicates sample has a reported value of 100 ppb by EPA 8021B,however,the EPA 8260B MTBE result on this sample is ND All of the data has been reviewed and no laboratory discrepancies were noted Based upon the data review,there was co-elution of MTBE with 3-methyl-pentane on the EPA 8021B analysis and the reported value of 100 ppb is a false positive The 8260B chromatogram and spectra have been reviewed for sample MW-10 and the MTBE result for this sample is ND 7 TPH-G,BTEX and MTBE by EPA Method 8260 8 Laboratory report indicates a hydrocarbon was present in the gasoline range that does not match the laboratory gasoline standard 9 All reports issued through the July 11,2002,event reported an incorrect screen interval of 25-35 feet The correct screen interval is 25-45 feet 4409 xlsl4180238 7 As of 07/28/03