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5 Conclusions <br /> Based on review of the laboratory analytical results generated as part of the TBA, the following <br /> conclusions are presented: <br /> • Arsenic is present in surface and subsurface soils up to 2.5 feet bgs at concentrations <br /> above the 2005 California EPA CHHSL for arsenic throughout the site. The <br /> concentrations of arsenic detected at the site are within the published range of naturally <br /> occurring concentrations for arsenic in soil. <br /> • TPH-d is present in the surface soil in the vicinity of boring location EC2-07, which is the <br /> roadway where the Fire Department parks their vehicles. It is likely that the surface soil <br /> contamination is related to historic fuel leaks from these vehicles. <br /> • TPH-d is present in groundwater throughout the site at concentrations above the 2008 <br /> RWQCB ESL for TPH-d. Based on a groundwater flow direction to the east-southeast, <br /> the former diesel UST that was located at the northwest corner of the fire station is the <br /> most likely source of the TPH-d contamination in groundwater found on site. <br /> • TPH-g is present in groundwater at boring location EC2-09, which is next to the former <br /> gasoline UST, at a concentration above the 2008 RWQCB ESL for TPH-g. It is likely that <br /> residual contamination from the former gasoline UST is the most likely source of TPH-g <br /> contamination in groundwater on site. <br /> • MTBE and 1,2-DCA is present in groundwater at boring location EC2-09, which is next <br /> to the former gasoline UST, at a concentration above the 2008 RWQCB ESL for MTBE <br /> and 1,2-DCA. It is likely that residual contamination from the former gasoline UST is the <br /> most likely source of MTBE and 1,2-DCA contamination in groundwater on site. <br /> • Concentrations of the COPCs not described above were below the site-specific screening <br /> levels selected for this assessment. <br /> 5-1 <br />