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S• {:,N'. 1 �{. 1 9"W'P' 1 Wi . _ � � C; L � �.�.'tr, d Y F, „�, <br /> 4 <br /> t" FINAL REbtET)IATUbN PIAN p <br /> Shell off Company <br /> 620 West Chm-ter Way,Stockton,California <br /> t Delta Project No-40438-586 <br /> Page 10 <br /> l <br /> E� Based on field screening measurements and laboratory analysis, it has been determined that petroleum <br /> constituents in the soils beneath the site have resulted from two source ir4.a!ions:the former pump islands <br /> to and the former underground storage tank locations. Four soil samples contained TPH concentrations greater <br /> than 3,000 parts per million(ppm)beneath the former tank locution. A soil sample collectrd in the area <br /> beneath the former pump islands (from the boring of monitoring well MW-9) at 20 feet below grade <br /> contained Tl?H concentrations of 4,400 ppm. The inferred subsurface extent of petroleum constituents in <br /> the soils underlying the site is illustrated on the crass-sections presented in Figures 5(A A)and 6(B-B'). <br /> Note that deeper soil samples collected from soil boring MW-2 may be affecteA by the presence of free <br /> product on the water table. All original laboratory data sheets for soil sampling at this site have been <br /> submitted in previous reports listed in Section 1.3 of this report <br /> t y 3.3 Site HydMgeoay_ <br /> f4769ti>kt4l has been monitored at the site since December 1959. The latest ground water levet <br /> measurements(December G,1990)indicate that depth to water ranges from 31.04 to 33.3 feet below grade. <br /> ) s) ratttuppe appmit( y 4tivt+een December 1989 and December 1990. <br /> tWater level measurements matte since December 1989 are compiled in Table 5. Water level measurements n <br /> made between December 1989 and September 1990 have indicated an inferred direction of ground water flow <br /> toward the north as indicated in Figure 7-A ith a hydraulic.gradient of approximately 4.022 foot per foot. <br /> However, ground water level measurements made in October and December 1990 indicate no definite <br /> f <br /> direction of ground water flow. Monitoring wells containing free product were not used in determining <br /> I a hydraulic gradient, <br /> t 3.4 Ground Water Analytical Results and Distributlortor Petroleum Constituents In Ground Water <br /> Ground water samples have been collected an a quarterly basis(December 1989,March,July,and October <br /> 1 = <br /> Flt 1990) and submitted to a certified laboratory for analysis of BT.EX and TPl•1 as gasoline. The analytical <br /> results of ground water samples collected since December 1989 are compiled in Table 6. <br /> i •, <br /> lx <br /> i <br /> ►R. <br /> 3 <br /> L. <br /> E <br /> r.r <br /> :r <br />