Appendix C. Models Routinely Used to Estimate Exposure Concentrations for Different Exposure Scenarios and Exposure Pathways

Section 6.2.2.2 discusses using models to estimate EPCs.

Table C-1. Models routinely used to estimate exposure concentrations for different exposure scenarios and exposure pathways
Exposure pathways	Models
Vapor Intrusion into Buildings	Generic empirical attenuation factors developed by USEPA (2012i) may be useful as a screening tool for predicting potential indoor air concentrations due to the migration of subsurface volatile chemicals into buildings through building foundations.
Vapor Intrusion into Buildings	Indoor air concentrations from the volatilization and migration of soil gas (from soil, groundwater or LNAPL) into a building can be estimated using the model described by Johnson and Ettinger (1991), which USEPA and other agencies recommend for screening evaluations (USEPA 2004c; ITRC 2007c; ITRC 2007d; NJDEP 2013; DTSC 2011b).
Vapor Emission from Exposed Water	Vapor emissions from exposed water surfaces in excavations can be modeled using the mass transfer coefficients recommended by USEPA (1995a).
Vapor Emission from Exposed Soil	Vapor emissions from exposed soil can be estimated using the Jury model (Jury, Spencer, and Farmer 1983; USEPA 1996b) based on depletion over time assuming that chemicals are present in the soil from the ground surface to an infinite depth. This model can be modified to estimate average vapor emissions over time assuming that chemicals are present in soil to a finite depth.
Air Dispersion	Average air concentrations can be estimated using empirical correlations presented in USEPA's Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites (USEPA 2002f).
Air Dispersion	”Worst-case” ambient air concentrations due to vapor emission from outdoor areas can be estimated using USEPA's AERSCREEN (USEPA 2011a).
Dust Emissions and Dust Concentrations	Emission of respirable soil particulates (PM10) from outdoor soil can be calculated using the wind erosion model recommended by USEPA (1996b).
Residential Garden Vegetable Uptake	The uptake of chemicals in soil by homegrown produce can be estimated using the methods outlined in USEPA guidance (2005c; 2005d). The uptake of chemicals in soil by homegrown produce can be calculated assuming that chemical concentrations are present in the entire root zone and the chemical concentrations do not deplete or deplete over time (Jury, Spencer, and Farmer 1983).

Publication Date: January 2015

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