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Table I Groundwater Monitoring Data and Analytical Results Tosco(Unocal)Service Station#5886 2701 West March Lane I' Stockton,California �k llf jf EXPLANATIONS f 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 DTW=Depth to Water TPH-G=Total Petroleum Hydrocarbons as Gasoline --=Not Measured/Not Analyzed - r (ft)=Feet B=Benzene ND = Not ietectedk S i =Screen Interval T=Toluene a � (ft bgs)=Feet Below Ground Surface E=EthylbenzeneG OWE=Groundwater Elevation X=Xylenes (msf)=Mean sea level MTBE=Methyl tertiary butyl ether �} G * The TQC 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 c1asing 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 i elevations for wells MW-1,MW-2 and MW-3 (MW-1=-0 84 feet msl, MW-2=-0 30 feet msl,and MW-3=-0 14 feet ms])and the resurveyed elevation of well MW-1 (=-1 35 feet msl) _ #22 to of 3/4"iron to ** Wells were re-surveyed on April 27, 1999 by Morrow Surveying TOC elevations are based on City of Stockton Benchmark 6, p p �i in monument box at the intersection of the centerline of Feather River and the S R 0 W line of March Lane,(Elevation=-0 92 feet) N ' Laboratory report indicates unidentified hydrocarbons unidentified hydrocarbons>C14 r xntified hydrocarbons unidentified hydrocarbons>C15 Laboratory report indicates unite y Y I Laboratory report indicates unidentified hydrocarbons diesel and unidentified hydrocarbons>C20 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 �I { I _ 6 TPH-D analysis with silica gel cleanup 7 MTBE by EPA Method 8260 Detection limit raised Refer to analytical reports v Laboratory report indicates unidentified hydrocarbons C9-C24 10 Laboratoryreport indicates unidentified hydrocarbons C9-C24 and Discrete peak @ C24 1 �F 11 Laboratory report indicates unidentified hydrocarbons C6-C12 12 Laboratory report indicates unidentified hydrocai bons>C16 13 MTBEby EPA Method 8260 required reanalysis past hold time due to failing internal standard on first run First analysis was within hold Wille j4 Laboratory report indicates discrete peaks 1` calibration failed Since silica cleanup was requested on diesel hits,the sample was not rerun The results should be considered estimated values Instrument continuing � 16 Laboratory report indicates MTBE reported from a second run dilution iC ti Laboratory report indicates sample was analyzed beyond the EPA recommended holding time 3 I � " 1120101 5686 x1137 I I YL