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4) No man-made conduits exist that would increase the vertical <br /> migration of leachate in the vicinity of Tank 874. A score of 10 <br /> is assigned to this site feature. <br /> 5) No unique site features exist that would influence downward <br /> ' migration. A score of 10 is assigned to this characteristic. <br /> ' The Tank 874 locale scored a total of 39 points for its leaching <br /> potential. Strictly interpreted, this indicates a "high leaching <br /> ' potential", leading to acceptable TPH and BTX&E levels of 100 ppm and <br /> 0.3/0.3/0.3/0.3 ppm, respectively. However, a score of 39 is close to the <br /> boundary separating the "medium leaching potential" and "high leaching <br /> potential" categories (Appendix B) . Therefore, it is proposed that the <br /> allowable contaminant concentrations specified for each category be <br /> interpolated. This results in acceptable clean-up levels for TPH and <br /> BTX&E of 500 ppm and 0.3/0.3/0.6/0.6 ppm, respectively. <br /> ' A soil sampling plan has been developed in accordance with the <br /> "Underground Tank Regulations" and guidance provided in the LUFT Field <br /> ' Manual. Sampling will occur prior to excavation of the tank. If analyses <br /> of all sampled material show TPH and BTX&E concentrations less than 500 <br /> ppm and 0.3/0.3/0.6/0.6 ppm, respectively, the fill and soil surrounding <br /> ' the tank system will be considered clean and no further sampling will <br /> occur. If analyses of sampled materials show contaminant concentrations <br /> greater than these values, the soil or fill materials represented by these <br /> samples will be removed and disposed of as hazardous waste. Additional <br /> ' sampling, and if necessary, additional excavation and resampling, will <br /> occur until analyses of samples taken below the excavation are shown to be <br /> clean. It may be necessary to remove the tank to permit removal of <br /> contaminated fill or soil materials. <br /> Soil samples will be taken from the following nine locations (see <br /> Figure 2) and analyzed for TPH and BTX&E concentrations using the <br /> Department of Health Services method described in Appendix C of the LUFT <br /> Field Manual and EPA Method 8020, respectively. <br /> Sample 1. From the north side of the tank just below the suspected <br /> leak site identified by the Precision Test and the Helium Test. This <br /> ' is considered the worst-case location. <br /> 5 <br />