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I 1 SECTIOMT E Technical Approach • what the potential concentrations in groundwater at different distances may be, a Tier 3 RBCA is proposed for the site In conducting a Tier 3 assessment, an alternative model is required and the Jury model is being proposed The Jury Behavior Assessment Mo del (Jury et al, 19$3) can be used to calculate chemical mass loading from sort to groundwater and volatile emission rates from sort The Jury model is a semi- analytical model that directly estimates contaminant leachate to groundwater and volatilization emissions to the atmosphere The model accurately conserves mass The results of the Jury model can be used as a check on the ASTM RBCA results and a potential range of model estimates can be used in the risk assessment Data requirements listing physical and chemical parameters for the Jury Model are listed in Tables 3-1 and 3-2 The loading rate (calculated in the Jury model) of contaminants from soil leaching to groundwater is used as input to the saturated zone model, AT123D (Yeh, 1981) AT123D is a semi-analytical model that uses site-specific data related to the contaminant source, saturated zone, and the distance to the receptor well to estimate concentrations in the well Data requirements for AT123D are listed in Table 3-3 The volatile emission rate from the Jury model is used as input to an air dispersion model, the Box Model Fate and transport modeling will be conducted for a 70-year time period Site-specific data will be used whenever available as input data for both the ASTM RBCA and Jury/AT123D modeling For input parameters that do not have site-specific data, either data from the literature or default values will be used that are protective of human health and the environment All input values will be referenced as to their source Results from ASTM RBCA and Jury will be compared with current Federal and State Maximum Contaminant Levels(MCLS)for drinking water 3.9.5 Estimate Chemical Intake for All Receptors Chemicals are typically taken into the bodies of human populations by inhalation, ingestion, and dermal contact The intake of chemicals will be estimated using site-specific data, appropriate assumptions, and guidance from U S EPA's Exposure Factors Handbook The estimated intake will be based on the receptor population's activity patterns,local meteorology, and land use issues Proposed intake assumptions are listed on Tables 34 through 3-7 ® rt,se7Yer A%STOCKTOtAtEPOftToocy7.ALK14M,ers009Nn%SNu► 3-6