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13 rl <br /> Ouarterly Groum water Monitoring Report <br /> 14800 West Frontage Road Manteca Caldomia <br /> i <br /> In August 1988, two soil borings were drilled and completed by ETS as groundwater <br /> I <br /> monitoring wells MW-1 and MW-2 In April and May 1989, Delta completed two additional <br /> soil borings as groundwater monitoring wells MW-3 and MW-4 in November 1989, Delta <br /> performed soil sampling during removal of three 10,000-gallon underground fuel storage <br /> tanks Delta completed four more soil borings as groundwater monitoring wells MW-5 <br /> through MW-8 in November and December 1989 The previous consultants' groundwater <br /> data, along with Aegis' data, is included in Table 1 In November 1991, Aegis drilled and <br /> completed groundwater monitoring well MW-9 (Figure 2) <br /> GROUNDWATER MONITORING <br /> On January 31, February 26, and March 24, 1992, Aegis personnel collected <br /> measurements of depths to groundwater in wells MW-1 through MW-9 Between <br /> December 19, 1991, and March 24, 1992, groundwater levels have fallen in all wells <br /> (Figure 3) an average of approximately 0 90-feet, ranging from 0 83 to 0 97-feet (Table 1) <br /> Figure 4 is a potentiometnc surface map of the shallow water-bearing zone on <br /> March 24, 1992 On the basis of these measurements, estimates of groundwater flow <br /> direction is to the southwest with a gradient of approximately 0 002 ft/ft The previous <br /> (December 19, 1991), quarter groundwater calculations were inconclusive as to gradient <br /> and direction <br /> Previous groundwater levels are summarized in Table 1 All groundwater elevation <br /> measurements were conducted according to the Aegis standard operating procedures <br /> (SOP) included in Attachment 1 <br /> WATER SAMPLING AND ANALYSIS <br /> I <br /> On January 31, 1992, Aegis personnel collected groundwater samples from wells MW-1 <br /> through MW-9 The samples were collected according to the Aegis SOP included in <br /> Attachment 1, and delivered under chain-of-custody to Net Pacific of Santa Rosa, <br /> California, a state-certified analytical laboratory The samples were analyzed for <br /> concentrations of <br /> • total petroleum hydrocarbons (TPH), as gasoline, by GC/FID Method 5030, <br /> and, <br /> • benzene, toluene, ethylbenzene, and total xylenes by EPA Method 8020 <br /> The laboratory analytical reports and chain-of-custody forms are included in Attachment 2 <br /> 90-097A pM R 2 <br />