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Ouarteriy Groundwater Monitoring Repoli ,ir X11 14800 West Frontage Road Manteca California ►1 „ In August 1988, two soil borings were drilled and completed by ETS as groundwater monitoring wells MW-1 and MW-2 In April and May 1989, Delta completed two additional soil borings as groundwater monitoring wells MW-3 and MW-4 In November 1989, Delta performed soil sampling during removal of three 10,000-gallon underground fuel storage tanks Delta completed four more soil borings as groundwater monitoring wells MW-5 through MW-8 in November and December 1989 The previous consultants' groundwater data, along with Aegis' data, is included in Table 1 In November 1991, Aegis drilled and completed groundwater monitoring well MW-9 (Figure 2) GROUNDWATER MONITORING On August 30, September 24, and October 21, 1991, Aegis personnel collected measurements of depths to groundwater in wells MW-1 through MW-8 On November 21 and December 19, 1991, Aegis personnel collected measurements of depths to groundwater in wells MW-1 through MW-9 Between July 22, 1991, and September 24, 1991, groundwater levels have risen in all wells (Figure 3) an average of approximately 1 24 feet, the rise in groundwater ranged from 0 89 to 2 01 feet (Table 1) Over the past 3 months, since September 24, 1991, groundwater levels have fallen in all wells (Figure 3) an average of approximately 3 03 feet, the fall in groundwater ranged from 2 59 to 3 76 feet (Table 1) On the basis of the October 21, 1991, measurements, calculated groundwater flow direction and gradient calculations are inconclusive Previous groundwater levels are summarized in Table 1 All groundwater elevation 9 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 October 21, 1991, Aegis personnel collected groundwater samples from wells MW-1 through MW-8 On November 21, 1991, Aegis personnel collected groundwater samples from wells MW-1 through MW-9 The samples were collected according to the Aegis SOP included in Attachment 1, and delivered under chain-of-custody to Net Pacific of Santa Rosa, California, a state-certified analytical laboratory The samples were analyzed for concentrations of a) total petroleum hydrocarbons (TPH), as gasoline, by Method GC/FID 5030, b) benzene, toluene, ethylbenzene, and total xylenes by EPA Method 8020, and c) total lead by EPA Method 7421 The analytical reports and chain-of-custody forms are included in Attachment 2 90-097F RFr 2 r