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L <br /> Oua►L"Groundwater I -dWring PWpad <br /> l+- 14800 West Frontage Road Manteca,California <br /> �l during the removal of three 10,000-gallon underground fuel storage tanks Delta installed <br /> four more monitoring wells, MW-5 through MW-8, in November and December 1989 <br /> Aegis began a program of monthly monitoring and quarterly sampling of the wells in <br /> January 1991 In November 1991, Aegis supervised drilling and completion of <br /> groundwater monitoring well MW-9 (Figure 2) The previous consultants' groundwater <br /> data, along with Aegis' data, is included in Table 1 <br /> GROUNDWATER MONITORING <br /> On October 20, 1992, Aegis personnel collected measurements of depths to groundwater <br /> 4n wells MW-1 through MW-9 Over the past month, groundwater levels have fallen in all <br /> wells (Figure 3) an average of approximately 0 79-feet, ranging from 0 50 to 1 10 feet <br /> (Table 1) Figure 4 is a potentiometric surface map of the shallow water-bearing zone on <br /> October 20, 1992 On the basis of the October 20, 1992, measurements, groundwater <br /> flow direction is estimated to be generally to the southwest, at a gradient of approximately <br /> 0 0008 ft/ft The current data indicate a reversal in flow direction since the previous <br /> measurements <br /> Groundwater measurements are summarized in Table 1 All groundwater elevation <br /> measurements were made according to the Aegis standard operating procedures (SOP) <br /> included in Attachment 1 <br /> WATER SAMPLING AND ANALYSIS <br /> On October 20, 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, Inc , 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/EPA Methods <br /> 5030/8015, and, <br /> • benzene, toluene, ethylbenzene, and total xylenes by EPA Method 8020 <br /> The analytical results are summarized in Table 2 The laboratory analytical reports and <br /> chain-of-custody forms are included in Attachment 2 Figure 5 is a distribution map of <br /> TPH, as gasoline, and benzene in groundwater based on the data summarized in Table 2 <br /> 90-097p QMR 2 <br />