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4 Working to Restore Nature RESNA began monitoring the groundwater in wells MW-1 through MW-4 in October 1991 ' (RESNA, June 26, 1991, Report 30004-4). Well MW-S was added to the monitoring program in March 1993. Dissolved hydrocarbons have been detected in monitoring wells MW-1 and MW-5 since monitoring began. In March 1992, EA Engineering, Science,.Technology (EA) observed removal of the oil- water separator/clarifier (EA Engineering, Science and Technology, August 1992, Report 80633.01). EA collected one soil sample from beneath the former oil-water separator and one sample from the concrete. Analytical results from the soil samples indicated that oil and grease (quantified as total oil and grease [TOG]) were present. Concentrations of volatile organic compounds,semi-volatile organic compounds,and polychlorinated biphenyls were below detection limits. Metal concentrations were also below detection limits with the exception of arsenic and barium which were detected at concentrations of 0.0051 and 0.12 parts per million, respectively. •' -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 soil beneath the site can be remediated by vapor extraction and the evaluated radius of influence was 30 feet. GROUNDWATER MONITORING, FIRST QUARTER 1994 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 RESNA. Field work included measuring depths to water and collecting groundwater samples for subjective and laboratory analyses. RESNA used these data to evaluate the direction and gradient of groundwater flow beneath the site. On April 8, 1994, a technician 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 to this report. The technician did not observe floating product or product sheen on samples collected from the wells (Table 1). The surveyed elevations of the top of casing and the depth-to-groundwater measurements (summarized in Table 1) were used to evaluate the potentiometric surface beneath the site. On April 8, 1994, the direction of groundwater flow was east with a gradient of approximately 0.002 (Plate 3). The direction of groundwater flow has generally been southeast since our investigation began. The groundwater surface has risen an average of 3.00 feet since the last monitoring event. Groundwater samples from each well were analyzed for benzene, toluene, ethylbenzene, and 4429=r/_VW4-11 2