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T1 Groundwater Monitortn and Analytical Results Tosca(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 TPH-D=Total Petroleum Hydrocarbons as Diesel (ppb)=Parts per billion (ft)=Feet TPH-G=Total Petroleum Hydrocarbons as Gasoline --=Not Measured/Not Analyzed DTW=Depth to Water B=Benzene ND = Not Detected S I =Screen Interval T=To]uene QA=Quality Assurance (ft bgs)=Feet Below Ground Surface E=Ethylbenzene GWE=Groundwater Elevation X=Xylenes (ms1)=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 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 i 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 msl, MW-2=-0'10 feet ms],and MW-'i=-0 14 feet msl)and the resurveyed elevation 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) I 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 ` Laboratory report indicates the hydrocarbons detected appeared to be a diesel non-diesel mixture b TPH-D analysis with silica gel cleanup 7 MTBE by EPA Method 8260 s 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 ii Laboratory report indicates unidentified hydrocarbons C6-C12 12 Laboratory report indicates unidentified hydrocarbons>C16 14 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 P; Instrument continuing calibration faded 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 17 Laboratory report indicates sample was analyzed beyond the EPA recommended holding time As of 08/02/02 5886 xla/#180137 19