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Jerry Lile <br /> March 3, 2014 <br /> Page 8 of 13 <br /> PAHs Uncertainties: Soil data collected from the Homes area in 1998 prior <br /> to development were insufficient for assessing risks, thus additional PAH <br /> data were collected from the ROW soil in 2007 and used as supporting <br /> data. Homes area risks may be higher or lower if the PAH soil data were <br /> more complete. PAH maximum concentrations are likely underestimated <br /> due to shortcomings on soil depths investigated, as discussed below. <br /> Potential cumulative residential risks from arsenic also were within the risk <br /> management range. The maximum arsenic concentration of 5.8 mg/kg is <br /> consistent with background in the extensive data sets evaluated by HERO <br /> (DTSC, 2009). Thus, HERO supports no further action with respect to <br /> arsenic in soil at the OVP pipeline near Surland Homes, but not PAHs. <br /> Residents' potential cumulative hazards slightly exceeded a Hazard Index <br /> (HI) of 1 due to TPHs, suggesting potential for non-carcinogenic effects <br /> from TPHs. A HI of 1 or less indicates the contaminant concentration <br /> levels correspond to no expected adverse effects for the human <br /> Population, including sensitive subpopulations, from exposures during a <br /> lifetime or portion of lifetime. <br /> TPH Uncertainties: Significant uncertainty exists in HERO's hazard <br /> estimates due to assumptions necessitated by lack of speciation of TPH <br /> soil concentrations into aliphatic and aromatic carbon range fractions. <br /> See discussion below on TPH-related uncertainties. <br /> Soil Depth Related Uncertainties: No shallow soil data are available from <br /> the Homes area. The soil data from the Surland Homes development <br /> were collected in 1998 and limited to sampling 6 to 7 ft below ground <br /> surface (bgs) with the exception of one 9 ft bgs sample; a total of four <br /> samples 4 samples were collected within the TPH impacted area. <br /> Subsequently, the land was developed into a residential subdivision. Soil <br /> depths of up to 10-12 feet below ground surface (bgs) may have been <br /> redistributed during redevelopment (USEPA, 1989b). Potential risks to <br /> residents from soil exposures may be underestimated because limited <br /> depths of soil were investigated. However, since the data are over 15 <br /> years old natural attenuation may have reduced concentrations of TPH <br /> and volatile chemicals, but not PAHs. <br /> The major uncertainties in HERO's risk estimates are due to data <br /> limitations and assumptions used in the risk evaluation because data were <br /> not available. Due to the age of the data, present TPH soil concentrations <br /> are anticipated to have naturally attenuated, although it is uncertain <br /> whether concentrations correspond to a HI less than 1. <br /> frle:20140303J L.doc <br />