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• Tb f Groundwater Monttoringa*and Analytical Results Tosco(Unocal) Service Station#5886 • 2701 West March Lane Stockton,California = EXPLANATI &S: 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 DTW=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 OWE=Groundwater Elevation msi=Mean sea level TPH(D)=Total Petroleum Hydrocarbons as Diesel ` TPH(G)=Total Petroleum Hydrocarbons as Gasoline * The TOC elevations were surveyed relative to Mean Sea Level(ms]) 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 msi 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 msi, MW-2=-0 30 feet ms],and MW-3=-014 feet msI)and the resurveyed elevation of well MWA (�I 35 feet ms]) ** Well 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 ROW 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 3 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 6 TPH(D)analysis with silica gel cleanup 7 MTBE by EPA Method 8260 8 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 `i Laboratory report indicates unidentified hydrocarbons C6-C12 L2 Laboratory report indicates unidentified hydrocarbons>C16 13 MTBE by EPA Method 8260 required reanalysis past hold time due to failing internal standard on first run First analysis was within hold time t4 Laboratory report indicates discrete peaks is 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 Note Wells designated as"S"are screened in the shallow zone,wells designated as"]"are screened in the intermediate zone,and wells designated as "D"are screened in the deep zone 5886 xls/#180I37 ii As of 08/04/00