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„� � (�wrdwaDer Marrl�Ortrq Ae�at . <br /> W1 F Street,9arda.CelVorru <br /> l Y. BACKGROUND <br /> Aegis has been conducting groundwater monitoring and sampling at the site since <br /> February 1, 1991. Work conducted 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 Levels <br /> On July 7, 1993, Aegis personnel collected measurements of the depths to groundwater <br /> in wells MW-1 through MW-6. Since the previous monitoring event in April 1993, <br /> groundwater levels have risen in all wells (Table 1, Figure 3) an average of approximately <br /> 1.02 feet; ranging from 0.98 to 1.06 feet. Based on the latest depth-to-groundwater <br /> measurements, the groundwater flow direction is estimated to be to the northeast (Figure <br /> 4) at an average gradient of approximately 0.0002 ft/ft. Figure 4 is a potentiometric <br /> surface map of the shallow water-bearing zone for July 7, 1993. } <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 /> i 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 July 7, 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 (BTEX) by <br /> modified EPA Method 8020; and c) TPH, as diesel, by GC-FID/EPA Methods 3510/8015. <br /> Well 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 /> 90-099G.OMR -2- <br /> f <br />