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=� [)tl f't�ttt 13ic�ti-�:�1�t�ls Page 19 ^- August 10, 1989 Job No.211-71-6 depth of approximately 58 to 62 feet below the existing grade at the site. Elevations of the potentiometric levels measured in the wells which do not contain free-floating product on June 19, 1989 range from a high of-7.42 feet to a low of-9.80 feet MSG The Ground-Water Gradient Map (Figure 6) shows potentiometric elevations and contours based on the wells at the site which do not contain free product. The Ground-Water Gradient.Map indicates that ground water generally flows towards the southeast with a gradient of approximately 1.5 foot/100 feet (ie., a gradient of 0.015). Anal ical Results- Soils The results of the soil chemical analyses are presented hi Appendix B and also swmzarized in Table E. A total of 69 soil samples collected from monitoring wells MW-15 through MW-25 and exploratory'borings B-1 through B-9 were analyzed for total petroleum hydrocarbons(as gasoline), benzene,ethylbenzene,toluene,and xylenes to better define the extent of soil contamination at the al results available from the previous monitoring wells site. There were only a few soil analytic installed at the site. Total petroleum hydrocarbon as gasoline (TPHg) levels in the soil samples ranged from non- - detected to a high of 8, 00 mg/kg (ppm)in boring B-5 at 25 1/2 feet. Figures 7, 8,and 9 show the lateral extent of TPHg soil contamination within the unsaturated zone at three depth intervals `- (i.e.,6 to 11 feet,25 to 31 feet,and 40 to 45 feet). Thesr maps are interpretive and were generated using the laboratory analytical results;non-detectable limits were substantiated using organic vapor W analyzer(OVA meter) results where laboratory analytical results are lacking. Figures 7, 8 and 9 _ show that thE,majority of the conEaminated soil occurs in the northern and west centra!portions of the site(near the underground fuel tanks and adjacent piping). The highest concentrations of TPHg in the soil remain in the vicinity of the underground tanks and the bulk rack piping. Plate 3 shows the boundaries and relative concentrations of the soil piume in cross see ion based on OVA readings taken from soil samples collected at approximately five foot intervals. The crass sections again show that the highest concentrations of hydrocarbons in.the soil occur in the vicinity of the underground fuel tanks but that the lateral extent of the soil contamination is greatest at a depth of 40 to 45 feet. The subsurface soils between 40 and 45 feet are highly interfingered and include silt,clayey silt,silty sand,'and sand. The greater lateral extent of hydrocarbon contamination 4t this depth may be attributable to prior shallower ground-water levels. Benzene levels in the soil samples ranged from non-detected to a high of 56 mg/kg(ppm)in boring; _ B-2 at 55 1/2 feet. The highest benzene concentrations were detected in samples obtained from borings B-1 through B-5 and monitoring well MW-17 (located in the immediate vicinity of the piping, undergrou►td fuel tanks,-the-adJacent' and - u -Fac ------ - Soil samples were also collected within the saturated zone and analyzed for TPHg and BETX -"� concentrations in order to help determine the verticai extent of ground-water contamination. All soil samples collected below a depth of 61 feet which were submitted for laboratory analyses yielded