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Groundwater Monitoring ju and Analytical Results Tosco(Former BP Oil)Service Station#11195 16500 South I-5 Lathrop,California EXPLANATIONS: Groundwater monitoring data and laboratory analytical results prior to May 20, 1999,(with the exception of September 3, 1998),were compiled from reports prepared by Blaine Tech,Inc. TPH-D=Total Petroleum Hydrocarbons as Diesel (ppb)=Parts per billion TOC=Top of Casing ND=Not Detected (ft.)=Feat TPH-G=Total Petroleum Hydrocarbons as Gasoline B=Benzene --=Not Measured/Not Analyzed DTW=Depth to Water CC=Conductor Casing S.I.=Screen Interval T=Toluene (ft.bgs)=Feet Below Ground Surface E=Ethylbenzene NP=No Purge GWE=Groundwater Elevation X=Xylenes QA=Quality Assurance/Trip Blank (ms])=Mean sea level MTBE=Methyl tertiary butyl ether On July 5,2002,the following wells were surveyed(MW-13,MW-14,MW-15,MW-16,and MW-17)by Virgil Chavez Land Surveying. The benchmark for this survey was a brass disk,stamped"City of Lathrop Bench Mark No.5,"at the southeast curb return of Louise Avenue and Harlan Road,(Benchmark Elevation=14.77 feet,NGVD 29). TOC elevations referenced to cross in sidewalk,run from City of Lathrop Benchmark No.5(Elevation=9.22 feet,msl). Prior to May 20, 1999,TOC elevations were referenced to San Joaquin datum,brass cap UV-34 at Mathey Road,45 feet north and 52 feet west of centerline(Elevation=12.50 feet above msl). MTBE by EPA Method 8260. 2 Laboratory report indicates discrete peak C6. 3 Detection limit raised. Refer to analytical reports. 4 MTBE by EPA Method 8260 analyzed dilution past recommended holding time. Initial analysis was within hold time. 5 Total Oil and Grease(TOG)was ND. 6 Halogenated Volatile Organic Compounds(HVOCs)were ND. 7 TOG was detected at 110 ppb. 9 Laboratory report indicates gasoline C6-C12. 9 Laboratory report indicates unidentified hydrocarbons C6-C 12. 10 MTBE reported from dilution run. 11 This sample was analyzed outside of the EPA recommended holding time. - 12 Laboratory report indicates weathered gasoline C6-C12. 13 TPH-G and BTEX by EPA Method 8260. 14 Laboratory report indicates a hydrocarbon pattern is present in the requested fuel quantitation range but does not resemble the pattem:of the requested fuel. 15 Well development performed. 16 TPH-G,BTEX and MTBE by EPA Method 8260. 17 Field Technician inadvertently missed well MW-8 for this event date. 1a TOC elevations were resurveyed in July 2002;data was provided on April 15,2003. GWE data for the following events 08115102, 11/18 -19/02,02/13-14103,and 02/21/03 have been changed to reflect the new elevations. 19 TOC was altered,do not use in contouring. 17 As of 05/13/03 11195.xls/#190175