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Quarterly Groundwater Monitoring Report 5491 F Street,Banta,CaWornia GROUNDWATER MONITORING Groundwater On November 21 and December 19, 1991, and January 17, 1992, Aegis personnel collected measurements of the depths to groundwater in wells MW-1 through MW-6. Over the past 3 months, since October 1991, groundwater levels have fallen in all wells (Table 1, Figure 3) an average of approximately 1.33 feet, ranging from 1.30 to 1.35 feet. Based on depth-to-groundwater measurements, the groundwater flow direction is estimated to be to the east (Figure 4) at an average gradient of approximately 0.0014 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. The wellhead elevations were surveyed by previous consultants or their agents and are referenced to mean sea level. Water Sampling and Analysis On January, 17, 1992, 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 under chain-of-custody to National Environmental Testing, Inc., 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/FED Method 5030; b) benzene, toluene, ethylbenzene, and total xylenes by EPA Method 8020; and, c) TPH, as diesel, 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. Concentrations of TPH, as gasoline and diesel, and benzene reported in Table 2 are also shown on Figure 5. 90-099D.RPT -2-