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IFinal Baseline Human Health Risk Assessment San Joaquin Human Services Agency Building December 2001 to the EPA and is referenced in this document as Environmental Quality Management (2000) The spreadsheets and accompanying user's guide were used to perform the indoor air dispersion modeling and risk-based calculations for the Human Services Agency site A description of the spreadsheet tools used to model concentrations from groundwater to indoor air are discussed in more detail below ' 3.1 Groundwater to Indoor Air Spreadsheet Tool The groundwater to indoor air modeling spreadsheet tool consists of a workbook in Microsoft, Excel The workbook used in this screening-level approach is called GW-ADV XLS The advanced model for groundwater contamination model was used since site-specific building ' parameters vary widely from the residential parameters used in the screening-level model The advanced model was populated with conservative default factors when model input parameters ' were not known, and site-specific factors for key variables such as building volume (width, length, height), air exchange rates, depth to groundwater, and groundwater temperature (see 10) Table 2) ' 3.2 Approach Indoor air modeling for current and future workers was conducted using the advanced ' groundwater model and site-specific input parameters obtained from regional- and site-specific sources Parameters and results are discussed in detail below 3.2.1 Site-Specific Parameters ' Groundwater to indoor air modeling and risk calculations were also performed for current and Ifuture indoor workers using site-specific parameters for both building and soil parameters(where available) The 90`h percentile concentration for benzene in groundwater (12 9 mg/L from a ' combination of MW-2 and MW-2A) was used as the site-specific exposure point concentration for the J&E screening model Due to the extreme variability across the site and even within the ' groundwater monitoring results in MW-2 and MW-2A, the use of the 90'h percentile is very . conservative These monitoring wells are located near the hot spot of a known fuel tank leak ' Monitoring at other locations around the building location have consistently yielded non-detect ' San Joaquin County GW Monitoring Report2(Appendix 17)v 2 3 12/27/2001