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Mr Kyle Chnsne Y Project 0$05-140 01 November 14, 1994 ' Page 2 On March 2, 1992, RESNA conducted a vapor extraction test at the site (RESNA, June 15, 1992, Report 30004-5) Results of the test Indicated that soli beneath the site can be remediated by vapor extraction and the evaluated radius of influence was 30 feet GROUNDWATER MONITORING, THIRD QUARTER 1994 1 Groundwater Technology, Inc , (GTI) Concord, California, was contracted by ARCO to conduct the ' field work at the site, GTI subsequently forwarded their field notes and the laboratory reports to EMCON Field work Included measuring depths to water and collecting groundwater samples for subjective and laboratory analyses EMCON used these data to evaluate the direction and gradient of ' groundwater flow beneath the site On September 23, 1994, a techrucian from GTI measured the depth to water and collected ' groundwater samples from monitoring wells MW-1 through MW-6 for subjective and laboratory analyses The field methods and procedures used are presented in an Attachment A The technician did not observe floating product or product sheen on samples collected from the wells (see Table 1) The surveyed elevations of the top of casing and the depth to groundwater measurements (summarmed in Table I) were used to evaluate the potentiomemc surface beneath the site On September 23, 1994, the direction of groundwater flow was east-southeast with a gradient of approximately 0 004 (see Figure 2) The direction of groundwater flow is consistent with previous sampling events Groundwater elevations decreased approximately 2 23 feet from the previous sampling event (June ' 1994) Groundwater samples from each well were analyzed for total petroleum hydrocarbons as gasoline (TPHG), and benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) using Environmental Protection Agency Methods 5030 and 8020 using DHS/LUFT Method The samples were analyzed at National Environmental Testing, Inc , in Santa Rosa, California. The results of these analyses are ' summarized in Table 1 Copies of the laboratory analysis reports are Attachment A ' Results of analyses indicated TPHG concentrations were detected in groundwater samples collected from wells MW-1. MW-3 and MW-5 at concentrations ranging from 110 parts per billion ([ppb] well MW-3) to 2,700 ppb (well MW-5) Benzene concentrations ranged from 4 6 ppb (well MW-1) to ' 400 ppb (well MW-5) TPHG and BTEX were not detected in wells MW-2, MW-4 and MW-6 Concentrations of benzene and TPHG are shown on Figure 2 ' WORK IN PROGRESS ' At the request of San Joaquin County Public Health Services information gathered during site investigations conducted at ARCO service station Nos 548 and 760 (225 South Cherokee Lane in Lodi, California) were reevaluated in an effort to address which site warrants the next available San Joaquin County designated ARCO vapor extraction treatment unit The results of this evaluation were presented in a report dated September 14, 1994 ARCO will continue quarterly monitoring The next ' sampling event is tentatively scheduled for December 1994 JAGpj0\0805\08051400 las-9411fc 5