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7 t <br /> 5491"F"Street,Banta.CaJdomia <br /> BACKGROUND <br /> Aegis was assigned as consultant, and resumed groundwater monitoring at the site, on <br /> February 1, 1991. Work performed at the site prior to February 1991 included <br /> investigations by Earth Treatment Systems, Inc., of Manteca, California, Delta <br /> Environmental Consultants, Inc.,of Rancho Cordova, California,and Nations Groundwater <br /> Associates of Sacramento, California. <br /> GROUNDWATER MONITORING <br /> Groundwater <br /> On October 20, 1992, Aegis personnel collected measurements of the depths to <br /> groundwater in wells MW-1 through MW-6. Since July 1992, groundwater levels have <br /> fallen in all wells (Table 1, Figure 3) an average of approximately 1.08 feet; ranging from <br /> 0.97 to 1.27 feet. Based on the depth-to-groundwater measurements, the groundwater <br /> flow direction is estimated to be to the east (Figure 4) at an average gradient of <br /> approximately 0.001 ft/ft. Figure 4 is a potentiometric surface map of the shallow water- <br /> bearing zone for October 20, 1992. <br /> Previous groundwater levels are summarized in Table 1. All depth-to-groundwater <br /> measurements were made from the referenced wellhead elevations, measured to the <br /> nearest 0.01 foot, and conducted according to the Aegis standard operating procedures <br /> (SOP) included in Attachment 1. <br /> Water Sampling and Analysis <br /> On October 20, 1992, Aegis personnel collected groundwater samples from monitoring <br /> wells MW-2 through MW-6. The samples were collected according to the Aegis SOP <br /> included in Attachment 1, and delivered under chain-of-custody to NET Pacific, Inc., of <br /> Santa Rosa, California, a state-certified analytical laboratory. The samples were analyzed <br /> for concentrations of: a) total petroleum hydrocarbons (TPH), as gasoline, by GC- <br /> FID/EPA Methods 5030/8015; b) benzene, toluene, ethylbenzene, and total xylenes by <br /> EPA Method 8020; and c) TPH, as diesel, by GC-FID/EPA Methods 3510/8015. Well <br /> MW-1 was not sampled due to the presence of floating liquid hydrocarbons. The <br /> analytical results are summarized in Table 2. The analytical reports and chain-of-custody <br /> form are included in Attachment 2. Concentrations of TPH, as gasoline and diesel, and <br /> benzene reported in Table 2 are also shown on Figure 5. <br /> 90-MD.OMR -2- <br />