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i Tab � Groundwater Monitoring16 and Analytical Results Tosca(Unocal)Service Station#5886 2701 West March Lane _ Stockton,California i EXPLANATIONS Groundwater monitoring data and laboratory analytical results prior to March 25, 1998,were compiled from reports prepared by MPDS Services,inc TOG=Top of Casing TPH-D=Total Petroleum Hydrocarbons as Diesel (ppb)=Parts per billion )= TPH-G=Total Petroleum Hydrocarbons as Gasoline _-=Not Measured/Not Analyzed (ftFeet B=Benzene ND Not Detected DTW=Depth to Water S i =Screen Interval T=Toluene QA=Quality Assurance/Trip Blank (ft bgs)=Feet Below Ground Surface E=Ethylbenzenc GWE=Groundwater Elevation X=Xylenes (msl)-Mean sea level MTBE=Methyl tertiary butyl ether * The TOC elevations were surveyed relative to msl These well casing elevations were used prior to the May 2, 1997 monitoring event The TQC elevations of the well casings were resurveyed(except for wells MW-2 and MW-3)relative to msl on April 28, 1997 The well casing elevations are used beginning with the May 2, 1997 The new TOC elevations for wells MW-2 and MW-3 were calculated by using the previously surveyed elevations for wells MW-1,MW-2 and MW-3(MW-1 =-0 84 feet mel, MW-2=-0 30 feet msl,and MW-3=-0 14 feet msl)and the resurveyed elevatton of well MW-i (=-1 35 feet msl) ** Wells were re-surveyed on April 27, 1999 by Morrow Surveying TOC elevations are based on City of Stockton Benchmark#226,top of 314"iron pin in monument box at the intersection of the centerline of Feather River and the S R O W line of March Lane,(Elevation=-0 92 feet) ' Laboratory report indicates unidentified hydrocarbons unidentified hydrocarbons>C14 2 Laboratory report indicates unidentified hydrocarbons unidentified hydrocarbons>C15 ' Laboratory report indicates unidentified hydrocarbons diesel and unidentified hydrocarbons>C20 4 Laboratory report indicates the hydrocarbons detected did not appear to be diesel 5 Laboratory report indicates the hydrocarbons detected appeared to be a diesel non-diesel mixture G TPH-D analysis with silica gel cleanup 7 MTBE by EPA Method 8260 R Detection limit raised Refer to analytical reports 9 Laboratory report indicates unidentified hydrocarbons C9-C24 to Laboratory report indicates unidentified hydrocarbons C9-C24 and Discrete peak Q C24 11 Laboratory report indicates unidentified hydrocarbons C6-Cl 2 12 Laboratory report indicates unidentified hydrocarbons>Cl6 'j MTBE by EPA Method 8260 required reanalysis past hold time due to failing internal standard on first run First analysis was within hold time 14 Laboratory report indicates discrete peaks 15 Instrument continuing calibration failed Since silica cleanup was requested on diesel hits,the sample was not rerun The results should be considered estimated values 16 Laboratory report indicates MTBE reported from a second run dilution t' Laboratory report indicates sample was analyzed beyond the EPA recommended holding time i 5986 xis/#180137 19 As of 02/23/03