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i • T � • Groundwater Momtorin and Analytical Results Former Tosco(Unocal)Service Station#6981 4707 Pacific Avenue Stockton,California EXPLANATIONS Groundwater monitoring data and laboratory analytical results prior to March 5, 1998,were compiled from reports prepared by MPDS Services,inc TOC=Top of Casing TPH-G=Total Petroleum Hydrocarbons as Gasoline (ppb)=Parts per billion (ft)=Feet B=Benzene ND=Not Detected DTW=Depth to Water T=Toluene --=Not Measured/Not Analyzed S I =Screen Interval E=Ethylbenzene NA = Not Available (ft bgs)=Feet Below Ground Surface X=Xylenes QA=Quality Assurance 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 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 I 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 9 Well was obstructed 9 Laboratory report Indicates gasoline and unidentified hydrocarbons>C8 `0 Laboratory report indicates gasoline and unidentified hydrocarbons C6-C8 tl Laboratory report indicates gasoline and unidentified hydrocarbons DC7 12 Laboratory report Indicates unidentified hydrocarbons>C7 r' Laboratory report indicates gasoline C6-C12 14 Laboratory report indicates weathered gasoline C6-C12 rs Laboratory report indicates discrete peaks if; 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 6981 xls/#180138 25 As of 49/30/02