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June 16, 1992 "ALAF <br /> - ARCO Station No. 548, Stockton, California <br /> with a hydraulic gradient of 0.004. Dissolved gasoline hydrocarbons have been analytically <br /> identified in ground-water samples collected-from(monitoring well MW_-T_� Dissolved <br /> gasoline hydrocarbons were not detected in groundwater samples collected from the <br /> remaining wells (RESNA, report in preparation). <br /> GROUND-WATER MONITORING <br /> A technician from Emcon visited the site on March 18, 1992, to take water-level <br /> measurements, perform subjective analyses of ground water, and collect ground-water <br /> samples from monitoring wells MW-1 through MW-4 for laboratory analyses. The field <br /> methods and procedures used are presented in an attachment to this report. The technician <br /> did not observe floating product or product sheen on samples collected from the wells <br /> (Table 1). . <br /> The surveyed elevations of the top of casing and the depth-to-ground-water measurements, <br /> summarized in Table 1, were used to evaluate the potentiometric surface beneath the site. <br /> ',On March 18, 1991; the direction of,ground-water flow beneath the site was south of easy <br /> with a gradient of approximately 0.003 (Plate 3). The direction of ground-water flow has <br /> generally been south of east since our investigation began. <br /> Groundwater samples from each well were analyzed for total petroleum hydrocarbons as <br /> gasoline (TPHg) and benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) <br /> using Environmental Protection Agency Method 5030/8020/DHS/LUFT Method. The <br /> samples were analyzed at Columbia Analytical Services, Inc. in San Jose, California <br /> (Hazardous Waste Testing Laboratory Certificate No. 1426). The results of these analyses <br />• are summarized in Tables 2. Copies of the laboratory analysis reports are attached. <br /> The results of analyses indicated TPHg and BTEX concentrations were below laboratory <br /> detection limits in ground-water samples collected from.-wells MW72 through MW-4�_ TPHg_! <br /> 4and BTEX were detected in_grou-nd-water samples collected from well MW-1.1 <br /> r <br /> WORK IN PROGRESS <br /> A�vapor extraction test'utilizing the three vapor-extraction wells was performed on March <br /> 3, 1992. The test was performed to evaluate vapor extraction as a soil remediation . <br /> alternative. The report describing the test procedures and results will be submitted to <br /> ARCO under separate cover. <br /> 0421ccar 2 <br /> 30004-6 <br />