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595 East 11 th Street, Tracy CA November 8, 1993 <br />'i <br /> Laboratory analyses results of the soil samples showed that TPHg concentrations ranging from 260 to 630 <br /> ppm Avere detected in soil bonngs SB-3, SB-5, SB-8, and SB-9, located dawn gradient, and to the north <br /> and north-east of the former UST locations The highest TPHg concentration (630 ppm) was found at <br /> bonng SB-8, located at the north-east corner of the site In addition, BTEX constituents were also <br /> detected at these locations Figure 3, is a TPHg concentration contour map illustrating the areas of <br /> hydrocarbon impacted soils Soil samples from bonngs located south and north-west of the former UST <br /> area (SB-1, S13-2, S13-6,and S13-7) did not contain TPHg or BTEX The TOG analysis performed on the <br /> sample from SB-3, located near the former waste oil tank, showed a concentration of 280 ppm In <br /> addition, results of the grab groundwater sample collected at boring B-2 show traces of ethyl-benzene and <br /> total, xylenes of 0 6 and 3 5 ppb, respectively <br /> FID field screening results of the soil bonngs showed that TVH concentrations ranging from 1,100 to <br /> 19,400 ppm were detected at bonngs SB-3, SB-4, SB-5, SB-8, and SB-9 These readings were taken at <br /> approximately the 9-feet depth interval A visual inspection of soils from these areas showed silver-gray <br /> soil discoloration indicative of soils that have been weathered by gasoline products Soil conditions <br /> generally consisted of clayey-silt to approximately 8-feet, underlain by saturated silty-sand and fine <br /> grained sand to approximately 10-feet <br /> RRM attempted to dnII three off-site soil borings located on the Tracy Union High School property <br /> HoNNe%er, the power actuated hand auger was not able to penetrate the shallow sub-surface soil layer <br /> CONCLUSIONS <br /> Main conclusions are as follows <br /> 1 Soils impacted by gasoline hydrocarbon products occur down gradient,to the north and north- <br /> east of the former UST area, primarily at the 7 to 10-feet depth interval(capillary fringe) Based <br /> on the TVH field screening and soil sample analyses results,soils at or near the groundwater <br /> surface(approumately 8-feet below surface grade)contain the highest levels of petroleum. <br /> hydrocarbons ,This data suggests that the source of down gradient soil contamination is from <br /> the impacted shallow groundwater <br /> 2 Based on soil sample results from bonngs located along the north boundary and north-ast comer <br /> of the subject site property,it is suspected that hydrocarbon impacts to soillgroundwater may <br /> extend off-site,and onto the Tracy Union High School Property <br /> 3 Soils located near the former waste oil tank area at boring SB-3 contained 280 ppm TOG <br /> 4 Soils not impacted by gasoline hydrocarbon products occur south and north-west of the former <br /> UST area at bon ng locations SB-1, SB-2, S13-6,and SB-7 The laboratory analysis results of the <br /> soil sample collected at SB-4 (located down-gradient of the former UST area)show that TPRg <br /> and BTEX were not detected This is most likely because the sample was collected at a depth of <br /> 10 5-feet below surface grade which was beneath the impacted soil zone that is located at <br /> approximately 7 0 to 10 0-feet, as confirmed by the TVH field screening reading of 12,050 ppm <br /> ry <br /> 0 <br /> 3 <br /> J <br />