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Jerry Lile <br /> March 3, 2014 <br /> Page 10 of 13 <br /> Soil Depth Related Uncertainties: Soil depth limitations, discussed above <br /> for residents, likely resulted in underestimated maximum soil <br /> concentrations for all COCs during sampling and analysis, and thus <br /> predicted risks to construction workers within the Surland Homes area. <br /> However, since the data are over 15 years old natural attenuation may <br /> have reduced concentrations of TPH and volatile chemicals. <br /> 2) Groundwater to Indoor air(residential) <br /> Predicted cumulative indoor air risks to current and future residents from <br /> groundwater in situ volatilization and migration to indoor air are also less than <br /> 1 x 10-6, however the cumulative hazard was well above 1 largely due to <br /> aliphatic TPHs. <br /> The major uncertainties in HERO's risk estimates are due to data limitations <br /> and assumptions used in the risk evaluation because data were not available. <br /> o TPH Uncertainties: Significant uncertainty exists in HERO's hazard <br /> estimates due to assumptions necessitated by lack of speciation of <br /> TPH groundwater concentrations into aliphatic and aromatic carbon <br /> range fractions. See discussion below on TPH-related uncertainties. <br /> o All groundwater data are from the Homes area, however the <br /> groundwater data were from 1998. Use of this data in HERO's <br /> screening level risk evaluation likely overestimates the hazards from <br /> TPH migration from groundwater to indoor air presented above <br /> because present concentrations are expected to be lower due to <br /> volatilization and natural attenuation. However, it is uncertain whether <br /> concentrations have reduced sufficiently to yield a HI of less than 1. <br /> 3) TPHs Uncertainties due to Soil and Groundwater Data <br /> TPHs are the dominant risk driver in groundwater and soil for current and <br /> potential future residents and construction workers, however these risks are <br /> based on 15 years old data. Current groundwater and soil TPH <br /> concentrations data are anticipated to be reduced from natural attenuation <br /> and hence demonstrate lower risks. Soil risks are currently anticipated to be <br /> lower due to landscaping, though cannot be confirmed with the data available. <br /> The absence of carbon fraction data for aliphatic and aromatic compounds, <br /> necessitated assumptions on the TPH composition to calculate risks. HERO <br /> assumed '/detected concentration was present as aliphatic and '/as <br /> aromatic TPH, using the most conservative (most toxic) aliphatic fraction (C9- <br /> file:209 40303J L.doe <br />