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Human Health Risk Assessment Former Mobil Oil Bulk Plant 04-343 500 East Grant Line Road Tracy, California The exposure pathway evaluation presented in this report consists o" a text description and calculations. The text description provides the assumptions, values, and sources of information used to estimate exposure. Calculations that quantify the exposure s Wenario are presented in Appendix D. In each of the calculations, the equations and parameters used to quantify exposure are presented. The third step in the exposure assessment process involves the quantil cation of exposure. As ' previously mentioned, this component quantifies the magnitude, frequency, and duration of exposure for each pathway identified. Generally, the quantification of exposure involves: ' 1) estimation of exposure concentrations, and 2) calculation of intake. The exposure point concentrations are estimated using environmental fate models. The calculation of intake is derived from equations that include parameters for exposure com;•entration, contact rate, ' exposure frequency, exposure duration, body weight, and exposure averaging time. The values of some of these parameters depend on site conditions and the charact(. istics of the potentially ' exposed populations. Descriptions of the parameters used to quantif exposure are presented in the following sections and in Appendix D. 5.2 IDENTIFICATION OF HUMAN EXPOSURE PATHWAYS ' The site is presently a fenced, vacant lot, located in a milieu of co amercial and industrial developments. Contiguous properties include: Vacant lots to the east •end west; Doane Product ' Company west and across the Southern Pacific Railroad; residential property northwest and across the Southern Pacific Railroad and East Grant Line Road; and ]L.eprino Foods north and ' across East Grant Line Road. Potential exposed receptors include moth current and future populations. The current receptors are working populations at nearby businesses, patrons of nearby businesses, residential populations northwest of the site; future receptors are either ' residents of an onsite house, or workers of an onsite business. ' Recapitulating from earlier sections, the residual concentrations of gasoline and diesel fuel range hydrocarbons have been detected in soil and ground water underlying the site. Approximately ' b,100 cubic yards of hydrocarbon-affected soil was removed from the sere and replaced with fill material. Subsequent site investigations have detected low dissoived-phase hydrocarbon concentration- in Monitorinu Well-, AW-`1 AW-9 AW-10 anrd AW. 1) W4C% 'nvPr 'rnu 30-0136-11 s-2 1 1