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QUARTERLY GROUNDWATER MONIIMNG A9a0RT 1399 East Yosemite Avenue Manteca California 4.0 GROUNDWATER MONITORING 41 Groundwater Aegis personnel collected measurements of the depths to groundwater in wells MW-1 B, MW-2, MW-3, MW-4, and MW-5 Over the past 3 months, since January 1992, groundwater levels have fallen in all wells (Figure 3) an average of approximately 1 02 feet (Table 1) On the basis of the April 9, 1992, measurements, groundwater is estimated to flow to the west (Figure 4) at an average gradient of approximately 0 0013 ft/ft For January 17, 1992, the flow direction was estimated to be to the northwest Il Previous groundwater levels are summarized in Table 1 All groundwater elevation 1� 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 as Appendix A Figure 4 is a potentiometric surface map of the shallow water-bearing zone on April 9, 1992 Groundwater monitoring well MW-1 B was not used i in the polestametric surface map due to an anomaly in the groundwater measurement ,I I 4 2 Water Sampling and Analysis On April 9, 1992, Aegis personnel collected groundwater samples from four of the five groundwater monitoring wells at the project site The samples were collected according to the Aegis SOP in Appendix A, and delivered under than-of-custody to NET Pacific, I Inc , of Santa Rosa, California, a state-certified laboratory, for chemical analyses MW1-B was not sampled due to the presence of floating liquid hydrocarbons The samples were analyzed for concentrations of total petroleum hydrocarbons (TPH), as gasoline, by GC/FID Method 5030, and, benzene, toluene, etnylbenzene, and total xylenes by EPA Method 8020 Groundwater analytical results obtained to date, including data reported by previous consultants, are summarized in Table 2 Concentrations of TPH, as gasoline, and y benzene reported for samples collected on April 9, 1992, are also shown on Figure 5 Copies of the laboratory analytical reports and chain-of-custody form are included in Appendix B fi 90 098A QMR -2 a� � i