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27 <br /> V <br /> 1 6.4 VERTICAL EXTENT OF SITE PETROLEUM HYDROCARBON IMPACTS <br /> 6 4.1 Soil Impacts <br /> At the direction of SJCPHS, boring NP-1 was located approximately 25 feet from the <br /> monitoring well with the current highest benzene concentration While this location posed the <br /> ' risk that the drilling would create a vertical contaminant pathway, it also provided a worse-case <br /> samphng point at which to delineate the vertical extent of impacts at the Site Table 5-1 and <br /> ' Figure 5-1 summarize the vertical delineation of the soil impacts beneath the Site as indicated <br /> by Simulprobe soil sampling results from boring NP-1 Detections of TPHg and benzene in <br /> samples taken from the saturated zone in boring NP-1 occurred at a depths of 40, 50, and 60 <br /> feet bgs Soil samples taken at three depths above (at depths of 10, 20, and 30 ft bgs) and <br /> below(at depths of 70, 80, and 90 ft bgs)were nondetect for both TPHg and benzene <br /> ' The NP-1 boring data indicate that the vertical extent of soil impacts has been <br /> delineated and that the impacts are comprised of a 30 foot thickness below 30 ft bfs and above <br /> 70 ft bgs <br /> ' 6.4.2 Groundwater Impacts <br /> Table 5-1 and Figure 5-2 summarize the vertical delineation of the groundwater <br /> impacts beneath the Site as indicated by the Sinulprobe grab sampling results from boring NP- <br /> ' 1 TPHg and benzene were detected in water samples taken from the saturated zone in boring <br /> NP-1 at depths of 50, 60, and 70 feet bgs Water sampling was also attempted at two depths <br /> ' above (at depths of 30 and 40 ft bgs) and two depths below at depths of 80 and 90 ft bgs) <br /> ' The formation at these depths did not yield water after a 20-25 minutes sampling interval Soil <br /> types noted in the boning logs indicate that moist, firm sandy clay and sandy silt was <br /> ' encountered at the 30 and 40 ft bgs depths, respectively Photoionization detector readings of <br /> 0 and 192 ppm, respectively, were recorded at the 30 and 40 ft bgs depths Slightly moist, <br /> ' moderate cemented silt with trace sand was encountered at the 80 and 90 ft bgs depths PID <br /> readings of 8 and 2, respectively, were recorded at the 80 and 90 ft bgs depths The <br />