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Jerry Lite <br /> March 3, 201 <br /> Page 7of13 <br /> b) HERO assessed vapor intrusion indoor air risks and hazards using a <br /> default attenuation factor (a) of 0.002 for current residents (CaIEPA, <br /> 2011) after estimating the vapor concentration (C„) just above the <br /> groundwater using Henry's Law. <br /> C, = CwxH' <br /> CW= water concentration <br /> H' = unitless Henry's Law Constant <br /> a = Cal( Cw x H') <br /> Ca = indoor air concentration <br /> Groundwater TPH data on carbon range fractions was not available, only <br /> TPH as gasoline (TPHg = C4-C12 = 1200 µg/l) analyzed from unfiltered <br /> groundwater and TPH as diesel (TPHd; C12-C24 = 520 µg/l) analyzed <br /> from filtered groundwater. As with soil, TPH risk evaluation was based <br /> on carbon range fractions as per Massachusetts DEP. HERO assumed <br /> '/2 detected concentration of TPHg was present as aliphatic and '/2 as <br /> aromatic TPH, using the most conservative (most toxic) aliphatic fraction <br /> (C9-C18) and aromatic fraction (Cs-C16)within the interval analytically <br /> quantified (C4-C24). <br /> B. HERO Results and Uncertainties <br /> 1) Soil <br /> a) Residents <br /> Predicted current and future residents' potential cumulative risks from <br /> hypothetical exposures to soil in the Homes Area (supplemented with <br /> metals and PAH data from the ROW) are above the federally established <br /> (40 CFR 300.430) risk management point of departure of 1 x 10"6 for <br /> cancer risk owing to PAHs. PAHs detected in the ROW but not the <br /> Homes area (benzo(a)pyrene and dibenz(a,h)anth racene) had detection <br /> limits (DLs) above risk-based concentrations in the Homes area, thereby <br /> necessitating use of'h DL as the concentration in the risk analysis. PAH <br /> data suggest risks from residential exposures to soil are within the risk <br /> management range of 1 x 10"6 to 1 x 10-4, but are inconclusive and likely <br /> underestimated due to data limitations (elevated detection limits in the <br /> 1998 data set from the Homes area and QA/QC recovery issues in the <br /> 2007 ROW data set). <br /> file:20140303J L.doc <br />