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Table 1 Groundwater Monitoring Data and Analytical Results Former,Unocal Semce Station#2859 1665 Pacific Avenue i i l Stockton,California EXPLANATIONS Groundwater monitoring data and laboratory analytical results prior to March i 6, 1998,were compiled from reports prepared by MPDS Services,Inc TOC=Top of Casing f B 1Benzene (ppb)=Parts per billion (ft =Feet it T�I Toluene ND=Not Detected DTW=Depth to Water I E�!Ethylbenzene (D)=Duplicate i --=Not Measured/Not Analyzed GWE=Groundwater Elevation X I�Xylenes (msl)=Mean sea level I, MfiBE=Methyl tertiary butyl ether QA=Quality Assuranceflnp Blank TPH-G=Total Petroleum Hydrocarbons as Gasoline { EB�=Equipment Blank * TOC elevations have been surveyed relative to mean sea level On Fet ruary 11110, 1999,TOC measurements were re-surveyed relative to City of Stockton BM#24, located in monument box at the northwest corner of Pacific Avenue aid Harding Way,(Benchmark Elevation=9 71 feet,NGVD29) On June 31,2001,the following wells were surveyed MW-4,MW-6 and MIWI -11 through MW-14 using the previous benchmark ' Laboratory report indicates the hydrocarbons detected appeared to be II gasoline and non-gasoline mixture Laboratory report indicates the hydrocarbons detected did not appear to be gasoline ` '- i 3 Detection limit raised Refer to analytical reports a MTBE by EPA Method 8260 i s Laboratory report indicates unidentified hydrocarbons C6-C12 I 6 Laboratory report indicates gasoline and unidentified hydrocarbons>C8 Well development only a Laboratory report indicates gasoline and unidentified hydrocarbons C6-C12 9 Laboratory report indicates discrete peaks h 10 Laboratory report indicates gasoline C6-C12 Laboratory report indicates weathered gasoline C6-C 12 i' Laboratory report indicates hydrocarbon pattem is present in the requested fuel quantitation range,but does not resemble the pattern of the requested fuel i} Laboratory report indicates the result was reported with a high bias due to the continuing calibration verification failing outside acceptance criteria 3, 14 Laboratory report indicates gasoline Cb-CIO � s Laboratory report indicates discrete peak @ C7 16 Current laboratory analytical results to not coincide with historical data,andlalthough the laboratory results were confirmed,it appears that the samples were switched 17 Laboratory report indicates discrete peak @ non-target @13 RT 's Laboratory report indicates discrete peak @ non-target @9 37 RT i ANALYTICAL METHODS EPA Method 8015 for TPH-G EPA Method 8020 for BTEX and MTBE{except where noted} EPA Method 8260 for MTBE(except where noted) 2859 x1s54 1� ,*27/03