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549- Street allorrM <br /> -&—t Rq= <br /> .%.W BACKGROUND <br /> Aegis was assigned as consultant, and resumed groundwater monitoring at the site, on <br /> February 1, 1991. Work conducted at the site prior to February 1.991 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 Levels <br /> On April 9, 1993, Aegis personnel collected measurements of the depths to groundwater <br /> in wells MW-1 through MW-6. Since January 1993, groundwater levels have risen in all <br /> wells (Table 1, Figure 3) an average of approximately 0.59-feet; ranging from 0.43 to 0.75- <br /> feet. Based on the latest depth-to-groundwater measurements, the groundwater flow <br /> direction is estimated to be to the east-northeast (Figure 4) at an average gradient of <br /> approximately 0.007 ft/ft. Figure 4 is a potentiometric surface map of the shallow water- <br /> bearing zone for April 9, 1993. <br /> Previous groundwater levels are summarized in Table 1. All depth-to-groundwater <br /> k <br /> w 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 SamRillng and Analysis <br /> On April 9, 1993, Aegis personnel collected groundwater samples from monitoring wells <br /> MW-2 through MW-6. The samples were collected according to the Aegis SOP included <br /> in Attachment 1. All the samples were submitted under chain-of-custody to Pace, Inc., <br /> of Novato, California, a state-certified analytical laboratory. The samples were analyzed <br /> for concentrations of: a) total petroleum hydrocarbons (TPH), as gasoline, by modified <br /> EPA Method 8015; b) benzene, toluene, ethylbenzene, and total xylenes by modified EPA <br /> Method 8020; and c) TPH, as diesel, by GC-FID/EPA Methods 3510/8015. Well MWA <br /> was not sampled due to the presence of floating liquid hydrocarbons. The analytical <br /> results are summarized in Table 2. The analytical reports and chain-of-custody form are <br /> included in Attachment 2. Concentrations of TPH, as gasoline and diesel, and benzene <br /> reported in Table 2 are also shown on Figure 5. <br /> 96-099F,QM R 2 <br />