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Ta Groundwater Monitoring ON and Analytical Results Former Tosco(Unocal)Service Station#6981 4707 Pacific Avenue Stockton, California EXPLANATIONS Groundwater monitoring data and laboratory analytical results prioi to March 5, 1998,were compiled from reports prepared by MPDS Services Inc TPH-G—Total Petroleum Hydrocaibons as Gasoline (ppb)=Parts per billion TOC=Top of Casing ND=Not Detected Feet B=Benzene (ft) T=Toluene --—Not Measured/Not Analyzed DTW=Depth to Water NA = Not Available S 1 =Screen Interval E=Ethylhenzene X=Xylenes QA=Quality AssuranielTrip Blank (ft bgs)=Heet Below Ground Surface y G WE=Groundw ater Elevation MTBE=Methyl tertiary butyl ether * TOC elevations have been surveyed relative to the City of Stockton Datum On September 9, 1999 and on September 30,2000,TOC elevations were re-surveyed based on City of Stockton Benchmark a brass cap in monument well on the east side of Pacific,Avenue approximately fifty feet south of March Lane (Elevation= It 56)City of Stockton datum I Laboratory ieport indicates the hydrocarbons detected did not appear to be gasoline The analytical results of the groundwater samples collected from monitoring wells MW-8 through MW 13 on January 17 and 18 1994,were inconsistent with the previous analytical results for these wells Therefore,MPDS Services,Inc resampled these wells on February 28, 1994 3 Laborator} has identified the presence of MTBE at a level above or equal to the taste and odor threshold of 40 ppb in the sample collected from this well 4 Covered by a new sidewalk 5 1 he positive result for gasoline does not appear to have a typical gasoline pattern 6 MTBE by EPA Method 8260 7 Field Blank B Well was obstructed 9 Laboratory report indicates gasoline and unidentified hydrocarbons>C8 10 Laboratory report indicates gasoline and unidentified hydrocarbons C6-C8 11 Laboratory report indicates gasoline and unidentified hydrocarbons<C7 12 Laboraton report indicates unidentified hydrocarbons>C7 1' Laboratory report indicates gasoline C6-C12 14 Laboratory report indicates weathered gasoline C6-C12 15 Laboratory report indicates discrete peaks 16 Laboratory report indicates unidentified hydrocarbons C6-C12 17 TPH-G and BTEX by EPA Method 8260 18 TPH-G BTEX and MTBE by EPA Method 8260 19 Laboratory report indicates a hydrocarbon pattern is present in the requested fuel quantitation range but does not resemble the pattern of the requested fuel 2 0 Laboratory report indicates that sample vials for MW-9 were not received,although documentation of the sample arriving at the laboratory is presented on the Chain of Custody As of 12/31/02 6981 xis/#180138 i