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.' ..E3ogr "sFF'-.�-a« _ - 'w.,�'Y° t{�'bz".y-s- r .y, nr _,aryvz�,. t'�r- K'`.'aR.a: a".a.•3+. ,s: <br /> Z— <br /> '7�.,n'a1 <br /> �.. . `" ',. . ... <br /> F;YE' <br /> ANAL RFMF.DIATION PIAN <br /> ! Shell Oil Company <br /> 620 West Charter Way,Stockton,California <br /> r Delta Project No.40 .586 <br /> t Page 10 <br /> 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 locations.the former pump islands <br /> and the forntr,,underground storage tank locations. Four soil samples contained TPH concentrations greater <br /> i than 3,OOC parts per million (ppm)beneath the former tank location. A soil sample collected in the area <br /> beneath the former pump islands (from the boring, of monitoring well MW-9) at 20 feet below grade <br /> 4=, <br /> V contained TPH concentrations of 4,400 ppm. The inferred subsurface extent of petroleum constituents in <br /> the soils underlying the site is illustrated on the cross-sections presented in Figures 5(A-A')and 6(B-B'). <br /> iv Note that deeper soil samples collected fr:)m soil boring MW-2 may be affected by the presence of free <br /> product on the water table. All original laboratory data sheets for soil sampling at this site have n;en <br /> -= submitted in previous reports listed in Section 1.3 of this report. <br /> 3.3 Slte IlvdroaeoloQv <br /> 'y water has been monitored at the site since December 1989. The latest ground water Level <br /> r measurements(December 6,1990)indicate that depth to water ranges from 31.04 to 33.3 feet below grade. <br /> :► :t44eba3 dct3pped.spproxtra> ely 4�.ieet between December 1489 and December 1990. <br /> .f Water level measurements made since December 1989 are compiled in Table 5. Water level measurements <br /> E <br /> made between December 1989 and September I990 have indicated an inferred direction of ground water flow <br /> toward the north as indicated in Figure 7 with a hydraulic gradient of approximately 0.022 foot per foot. <br /> ! a <br /> However, ground water level measurements made in October and December 1990 indicate no definite <br /> direction of ground water flow. Monitoring wells containing free product were not used in determining <br /> I'm hydraulic gradient. <br /> 3.4 Gt sund Water Anal licat Results and Distribution or Petroleum Constituents In Ground Water <br /> Ground water samples have been collected on a quarterly basis(December 1989,Nlarch,July,and October <br /> 1990)and submitted to a certified laboratory for analysis of BTEX and TPH as gasoline. The analytical <br /> results of ground water samples collected since December 1989 are compiled in'Table 6. <br />