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a <br /> dn+ <br /> 3.0 <br /> DATA ANALYSIS <br /> 3.1 CHEMICALS OF CONCERN <br /> The first step of the risk assessment was to review recently collected data specific to the <br /> site. The objective of the data evaluation was to identify chemicals.of concern that were <br /> related to the two former underground storage tanks. Data collected from October 21 <br /> through November 23, 1994 were used for the risk assessment. Fifty-seven soil samples <br /> from the vicinity of the tanks were evaluated for use in the risk assessment. Details on <br /> the sampling and analysis can be found in an another report (Woodward-Clyde 1995 <br /> ` Volume I of this report). Soil samples collected October 4 through October 18, 1994 <br /> were not used in the risk assessment because they were excavated. <br /> L- <br /> Risk assessments for sites contaminated with petroleum products are complicated by a <br /> general lack of information relevant to exposure to and toxicity of petroleum mixtures, <br /> especially Total Petroleum Hydrocarbons (TPH). Benzene, ethylbenzene, toluene, and <br /> xylene (BTEX) are frequently used to represent TPH in the environment. BTEX was <br /> r quantified separately from TPH for the YFS site and will be used in the risk assessment. <br /> Of the 57 soil samples, only eight had detectable levels of toluene, ethylbenzene, and <br /> total xylene. Benzene was detected in only one of the 57 soil samples. Three soil <br /> - samples detected TPH as diesel that did not detect BTEX. Polynuclear aromatic <br /> hydrocarbons (PAHs) were not analyzed for in the samples. Although PAHs are toxic <br /> they are not very mobile nor volatile. Impacts from potential PAHs would be expected <br /> to be insignificant based on their transport properties. <br /> 3.2 DATA EVALUATION <br /> All data have been validated and only those reliable data were used in the_quantitative <br /> risk assessment (EPA 1989b, 1990). To quantify analyte average concentrations, a value <br /> of one half the Detection Limit (DL) was used when the sample was reported as not <br /> being detected. This is consistent with EPA guidance (EPA 1989b). The 95 percent <br /> upper confidence limit (UCL) of the arithmetic mean was calculated using the eight soil <br /> [ S:\LDC\YELLO.RPT May 4, 1995 3-1 <br /> C <br />