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s_a ; 511 IIR f , asuterty Groancf der Mortatirg Report 5491 F Street,Banta,California GROUNDWATER MONITORING Groundwater On October 21, November 21, and December 19, 1991, Aegis personnel collected measurements of the depths to groundwater in wells MW-1 through MW-6. Over the past 3 months, since September 24, 1991, groundwater levels have fallen in all wells (Table 1, Figure 3) an average of approximately 1.89 feet. Based on depth-to-groundwater measurements, the groundwater flow direction is estimated to be to the east (Figure 4) s at an average gradient of approximately 0.001 ft/ft. Figure 4 is a potentiometric surface map of the shallow water-bearing zone. Previous groundwater levels are summarized in Table 1. All depth-to-groundwater measurements were made from the referenced wellhead elevations, measured to the nearest 0.01 foot, and conducted according to the Aegis standard operating procedures (SOP) included in Attachment 1. Wellhead elevations, surveyed by previous consultants or their agents, are referenced to mean sea level. Water Sampling and Analysis On October 21, 1991, Aegis personnel collected groundwater samples from monitoring ��- wells MW-1 through MW-6. The samples were collected according to the Aegis SOP included in Attachment 1,and delivered lander chain-of-custody to National Environmental Testing, Inc. (NET), of Santa Rosa, California, a state-certified analytical laboratory. The samples were analyzed for concentrations of: a)total petroleum hydrocarbons(TPH),as gasoline, by GC/FID Method 5030; b) benzene, toluene, ethylbenzene, total xylenes (STEX) by EPA Method 8020; and, c) TPH, as diesel and motor oil, by GC/FID Method 3510. The analytical results are summarized in Table 2. The analytical reports and chain-of-custody form are included in Attachment 2. ;L 90-099C.RPT