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• Phase II Environmental Site Assessment
<br /> Mountain House Neighborhood G
<br /> July 9,2002
<br /> Page 7
<br /> children would be exposed for 18 years, 365 days per year. Using these default factors, this screening
<br /> evaluation quantifies the potential lifetime risk and hazard from site conditions for a defined set of
<br /> exposure pathways. Pathways of exposure evaluated by this method are 1) inhalation of airborne dust from
<br /> soils, 2) incidental ingestion of soil, and 3) dermal absorption by direct contact with soil. Water pathways
<br /> were not evaluated based on consultation with a DTSC Risk Manager on similar projects completed by
<br /> Condor, and for reasons stated in Section 3.0. Exposure point concentrations were taken as the highest
<br /> concentrations of any soil contaminant in all soil samples collected from the 294acre site.
<br /> 7.2 RISK AND HAZARD CHARACTERIZATION
<br /> 7.2.1 Identification of Chemicals of Potential Concern
<br /> Chemicals of potential concern(COPC) were identified as the pesticides and herbicide detected at the site
<br /> (gamma-BHC, DDD, DDE, DDT,endosulfan I,endosulfan II, endrin, endrin aldehyde,heptachlor, kepone,
<br /> MCPP, azinphos-methyl, bolstar, chlorpyrifos, coumaphos, demeton, diazinon, dimethoate, disulfoton,
<br /> ethoprop, ethyl parathion, famphur, fensulfothion, fenthion, merphos, methyl parathion, mevinphos,
<br /> 0,0,0-triethylpitosphorothioate, tetrachlorvinphos, thionazin,tokuthion, and thrichloronate). Human health
<br /> risk assessment (HHRA) calculations were performed on these constituents identified as COPC, except for
<br /> those without published toxicity reference values.
<br /> The concentration in the exposure media used for the exposure assessment was the highest concentration
<br /> detected at the site. For inhalation exposure to dusts, a dust-in-air concentration of 50µg/m3 was assumed
<br /> (PEA Guidance Manual pg. 2-25).
<br /> 7.2.2 Exposure Assessment Methods
<br /> Conceptual Site Model
<br /> As shown below, all soil pathways discussed in the Cal/EPA PEA Guidance Manual were evaluated for
<br /> residential exposure as mandated by Cal/EPA for school assessments.
<br /> Source Media Pathway Receptors
<br /> pesticide soil ingestion, dermal absorption residents
<br /> application dust in air inhalation residents
<br /> metals soil ingestion, dermal absorption residents
<br /> soil dust in air inhalation residents
<br /> Exposure Assessment Calculations
<br /> As calculated in the spreadsheets included in Appendix B, the residential exposure scenario included an 18-
<br /> year exposure period for a child of highest soil ingestion (200 mg/day) per body weight (15 kg).
<br /> Additionally, a 30-year exposure duration was assessed for adults by using a soil ingestion rate of 100
<br /> mg/day and an adult body weight of 70 kg.
<br /> As shown in the calculations included in Appendix B, the Cal/EPA PEA defaults for dermal surface area,
<br /> adherence, and dermal penetration were used in calculating dermal doses. Airborne soil was assumed to be
<br /> at the Cal EPA default value of 50 µg/m'. The CaVEPA PEA default rate of 10 m'/day for a child and 20
<br /> M'/day for an adult were used as default inhalation rates (Cal EPA, 1999). Exposure analysis calculation
<br /> ( methods are those of Cal EPA (Jan. 1999) as performed by Excel spreadsheets included in Appendix B.
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