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Tab! . Groundwater Monitoring D nd Analytical Results 4 Former Tosco(Unocal)Service Station#6981 4707 Pacific Avenue Stockton,California I I EXPLANATIONS Groundwater monitoring data and laboratory analytical results prior to March 5, 1998,were compiled from reports prepared by MPDS Services,Inc TPH-G=Total Petroleum Hydrocarbons as Gasoline (ppb)=Parts per billion TOC=Top of Casing ND=Not Detected (ft)=Feet B=Benzene - T=Toluene -=Not Measured/1�Eot Analyzed DTW=Depth to Water NA = Not Available S 1 =Screen Interval E=Ethylbenzene (ft bgs)=Feet Below Ground Surface X=Xylenes QA=Quality Assurance/Trip Blank GWE=Groundwater 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= 11 56)City of Stockton datum I 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 MWA 3 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 5 The positive result for gasoline does not appear to have a typical gasoline pattern 6 MTBE by EPA Method 8260 7 Field Blank 8 Well was obstructed 9 Laboratory report indicates gasoline and unidentified hydrocarbons>C8 i0 Laboratory report indicates gasoline and unidentified hydrocarbons C6-C8 I it Laboratory report indicates gasoline and unidentified hydrocarbons<C7 12 Laboratory report indicates unidentified hydrocarbons>C7 13 Laboratory report indicates gasoline C6-C12 14 Laboratory report indicates weathered gasoline C6-C12 1s Laboratory report indicates discrete peaks 16 Laboratory report indicates unidentified hydrocarbons C6-C12 " 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 'n 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 6981 xis/#180138 27 As of 09/25/03