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Ta1 Groundwater MonitoringW and Analytical Results Former Unocal Service Station#80187 437 East Miner Avenue Stockton,California Groundwater monitoring data and laboratory analytical results prior to March 9, 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 DTW=Depth to Water B=Benzene --=Not Measured/Not Analyzed (ft.)=Feet T=Toluene (D)=Duplicate S i =Screen Interval E=Ethyibenzene (ft bgs)=Feet Below Ground Surface X=Xylenes GWE=Groundwater Elevation MTBE=Methyl tertiary butyl ether (msl)=Mean sea level I * TOC elevations have been surveyed relative to Benchmark marked"IS-9"1n monument box at San Joaquin and Oak Streets,(Elevation=10 523 feet,msl) Site re-surveyed on February 10, 1999 by Field Designs TOC elevations were surveyed on November 16,2000,by Virgil Chavez Land Surveying using the previous Benchmark GWE corrected due to the presence of free product, correction factor [(DTW-TOC)+(Product Thickness x 0 75)] I Laboratory reported the hydrocarbons detected appeared to be a gasoline and non-gasoline mixture 2 Laboratory reported the hydrocarbons detected did not appear to be gasoline 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 MTBE by EPA Method 8260 5 Laboratory report indicates gas and unidentified hydrocarbons<C7 6 Laboratory report indicates discrete peak C6 7 Laboratory report indicates unidentified hydrocarbons C6-C12 R Laboratory report indicates gasoline and unidentified hydrocarbons C6-C12 9 Well development performed 10 Laboratory report indicates gasoline C6-C12 11 Laboratory report indicates weathered gasoline C6-C 12 12 Detection limit raised Refer to analytical reports 13 Laboratory report indicates gasoline C6-C 12+unidentified hydrocarbons<C6 19 Laboratory report indicates gasoline C6-C12+unidentified hydrocarbons C6-C12 1s Detection limit raised due to high levels of non-target compounds Refer to analytical reports 16 Sample collected from bottom of well using discrete bomb sampler at 114 feet 17 Sample collected from bottom of well using discrete bomb sampler at 69 feet iR Well development not completed DTW only 19 Sample collected at the top of water column using a disposable bailer 0 18 7 xis/#280045 21 As of 11/28/01 I