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Table I ' . Groundwater Monitoringnd Analytical Results Former Tosco(Unocal) rvice Station#6981 4707 Pacific Avenue Stockton,California EXPLANATIONS' Groundwater monitoring data and laboratory analyhcal results prior to March 5, 1998,were compiled from reports Prepared by MPDS Services,Inc �billion (ppb)=Parts p TOC=Top of Casing TPH-G=Total Petroleum Hydrocarbons as Gasoline ND=Not Detected (ft)=Feet B=Benzene --=Not Measured/Not Analyzed DTW=Depth to Water T=TolueneNA = Nat Available S I =Screen interval E=Ethylbenzene QA=Quality Assurance./fnp Blank X=Xylenes (ft bgs)=Feet Below Ground Surface MTBE—Methyl teary butyl ether GWE=Groundwater Elevation tertiary * 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=11 56)City of Stockton datum 1 Laboratory report indicates the hydrocarbons detected did not appear to be gasoline 2 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 Laboratory 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 S The positive result for gasoline does not appear to have atypical gasoline pattern 6 MTBE by EPA Method 8260 7 Field Blank s 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 Laboratory report indicates unidentified hydrocarbons>C7 13 Laboratory report indicates gasoline C6-C 12 14 Laboratory report indicates weathered gasoline C6-C 12 13 Laboratory report indicates discrete peaks i6 Laboratory report indicates unidentified hydrocarbons C6-C 12 17 TPH-G and BTEX by EPA Method 8260 is 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 20 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 25 6981 als/#180138 I