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Jerry Lile <br /> March 3, 2014 <br /> Page 6 of 13 <br /> Direct contact with groundwater was not evaluated due to the incomplete <br /> exposure pathways (current and future) resulting from the City of Tracy <br /> ordinance prohibiting installation of wells for drinking water purposes. <br /> 1) Soil <br /> a) HERO evaluated screening-level risk to residents using (1) the data <br /> available for the Surland Homes area, (2) data available for the ROW, <br /> and (3) the combined Homes and ROW data set. Data gaps make the <br /> Homes data insufficient for risk assessment, thus data from the ROW, at <br /> the source area, were used in lieu of data from the Homes area; data <br /> from the source area are expected to be more conservative than from <br /> the more,distant soils in the Homes area. <br /> b) For both residents and construction workers, HERO used the maximum <br /> soil concentrations. Soil data were insufficient to calculate 95% upper <br /> confidence limits on the arithmetic mean concentrations (95%UCLs) for <br /> residents. <br /> c) TPH risk evaluation was based on the toxicities of carbon range fractions <br /> as per Massachusetts Department of Environmental Protection <br /> (MassDEP, 2003). In the absence of speciation into aliphatic and <br /> aromatic fractions, HERO assumed TPH results from the ROW(C10-C36) <br /> of 6300 mg/kg (Lancaster Labs results in SAIC, 2007) and from the <br /> Homes area (Cs-C36) of 3600 mg/kg were present as '/ the detected <br /> concentration as aliphatic and '/ as aromatic TPH, using the most <br /> conservative (most toxic) aliphatic fraction (C9-C1a) and aromatic fraction <br /> (C9-C16) within the C10-C36 and C8-C36 intervals. That is, toxicity criteria <br /> are available from two carbon ranges for both the aliphatic hydrocarbons <br /> and aliphatic hydrocarbons within the C10-C36 and Ca-C36 intervals that <br /> the analytical data correspond to, however the C19-C32 aliphatic and the <br /> C17-C32 aromatic fractions are less toxic. Recently, DTSC has issued <br /> recommended TPH toxicity criteria (DTSC, 2013); most are identical to <br /> the MassDep criteria, however a few are slightly less conservative. Use <br /> of the recently released DTSC values would not alter the outcome of the <br /> screening level risk evaluation presented herein. <br /> 2) Groundwater to Indoor Air <br /> a) HERO used the maximum groundwater concentrations from Geomatirx <br /> (1999) data presented in the 2009 H H S E (Appendix A). <br /> file:20140303J L.doc <br />