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We 1 I Groundwater MorntollWData and Analytical Results • Tosco(Unocal)Service Station#5886 2701 West March Lane Stockton,California EXPLANATIONS Groundwater monitoring data and laboratory analytical results prior to March 25, 1998,were compiled from reports prepared by MPDS Services,Inc TOC=Top of Casing B=Benzene (ppb)=Parts per billion DTV=Depth to Water T=Toluene --=Not Measured/Not Analyzed (ft)=Feet E=Ethylbenzene ND = Not Detected S I =Screen Interval X=Xylenes (ft bgs)=Feet Below Ground Surface MTBE=Methyl tertiary butyl ether GWE=Groundwater Elevation (msl)=Mean sea level TPH-D=Total Petroleum Hydrocarbons as Diesel TPH-G=Total Petroleum Hydrocarbons as Gasoline * The TOC elevations were surveyed relative to msl These well casing elevations were used prior to the May 2, 1997 monitoring event The TOC 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-I =-0 84 feet ms), MW-2=-0 30 feet msl,and MW-3=-0 14 feet msl)and the resurveyed elevation of well MW-1 (=-I 35 feet msl) ** Wells were re-surveyed on April 27, I999 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 unidenttfied hydrocarbons>C14 Laboratory report indicates unidentified hydrocarbons unidentified hydrocarbons>C15 ° Laboratory report indicates unidentified hydrocarbons diesel and unidentified hydrocarbons>C20 Laboratory report indicates the hydrocarbons detected did not appear to be diesel s Laboratory report indicates the hydrocarbons detected appeared to be a diesel non-diesel mixture fi TPH-D analysts with silica gel cleanup 7 MTBE by EPA Method 8260 x Detection limit raised Refer to analytical reports 9 Laboratory report indicates unidentified hydrocarbons C9-C24 10 Laboratory report indicates unidentified hydrocarbons C9-C24 and Discrete peak @ C24 11 Laboratory report indicates unidentified hydrocarbons C6-C12 12 Laboratory report indicates unidentified hydrocarbons>C16 " 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 5886 xls/#180137 13 Ac of 02/06/01