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i Ta Groundwater Monitoring and Analytical Results Tosco(Unocal)Service Station#6981 4707 Pacific Avenue Stockton,California EXPLANATIONS: Groundwater momtonng data and laboratory analytical results prior to March 5,1998,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 ND=Not Detected (ft)=Feet E=Ethylberizene --=Not Measured/Not Analyzed S 1 =Screen interval X=Xylenes NA = Not Available (ft bgs)=Feet Below Ground Surface MTBE=Methyl tertiary butyl ether GWE=Groundwater Elevation TPH(G)=Total Petroleum Hydrocarbons as Gasoline * 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 mconsistent 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 3 The positive result for gasoline does not appear to have a typical gasoline pattern 6 MTBE by EPA Method 8260 7 Field Blank s Well was obstructed s 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-C12 14 Laboratory report indicates weathered gasoline C6-C 12 13 Laboratory report indicates discrete peaks 16 Laboratory report indicates unidentified hydrocarbons C6-C12 6981 xlst*180138 21 As of 09/23/00