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r i Quarterly Groundwater Monitoring Report 5491 F Street,Banta,California BACKGROUND Aegis was assigned as consultant, and resumed groundwater monitoring at the site, on February1 1 1. 99 Work performed at the it p site prior to February 1991 included investigations by Earth Treatment Systems, Inc., of Manteca, California, Delta E Environmental Consultants, Inc., of Rancho Cordova, California, and Nations Groundwater Associates of Sacramento, California. GROUNDWATER MONITORING Groundwater On January 22, 1993, Aegis personnel collected measurements of the depths to groundwater in wells MW-1 through MW-6. Since October 1992, groundwater levels have fallen in all wells (Table 1, Figure 3) an average of approximately 0.22-feet; ranging from 0.10 to 0.33-feet. Based on the latest depth-to-groundwater measurements, the groundwater flow direction is estimated to be to the southeast (Figure 4) at an average gradient of approximately 0.002 ft/ft. Figure 4 is a potentiometric surface map of the shallow water-bearing zone for January 22, 1993. 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. Water Sampling and Analysis On January 22, 1993, Aegis personnel collected groundwater samples from monitoring wells MW-2 through MW-6 and domestic well DW-1. The monitoring well samples were collected according to the Aegis SOP included in Attachment 1. The domestic well was sampled at the hosebib located on the northwest corner of the residence after allowing the water to run for 15 minutes in order to obtain the most representative sample possible of the groundwater. All the samples were submitted under chain-of-custody to Pace, Inc., of Novato, California, a state-certified analytical laboratory. The samples were analyzed for concentrations of: a) total petroleum hydrocarbons (TPH), as gasoline, by modified EPA Method 8015; b) benzene, toluene, ethylbenzene, and total xylenes by modified EPA Method 8020; and c) TPH, as diesel, by GC-FID/EPA Methods 3510/8015. Well MW-1 was not sampled due to the presence of floating liquid hydrocarbons. The analytical results are summarized in Table 2. The analytical reports and chain-of-custody form are included in Attachment 2. With the exception of DW-1, concentrations of TPH, as gasoline and diesel, and benzene reported in Table 2 are also shown on Figure 5. 90-099E.QMR -2- '