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Ir Y L. 3.4 TRANSPORT MECHANISMS The primary transport mechanisms for the residual contamination at the Site are advection, adsorption, desorption, and volatilization. Residual petroleum hydrocarbons in the vadose zone can leach to groundwater or volatilize into soil vapor. Residual contamination in the vicinity of +. the former UST excavation can migrate downgradient in groundwater primarily through advection. The soil and groundwater data indicate that both media are affected, and consequently adsorption and desorption between the two phases may be occurring. Petroleum hydrocarbons (particularly TPH-g and BTEX) may volatilize from soil and/or groundwater into soil vapor. Volatilization of petroleum hydrocarbons from soil and groundwater into the vapor pore space may result in the subsequent migration to the ground surface. .. � b -u-1 qwpl41f" 3.5 POTENTIAL EXPOSURE PATHWAYS AND RECEPTORS cave" .r i4, ' v„� ti.. Potential exposure pathways and receptors at the Site and neighboring properties were evaluated based on current and potential future usage. The Site is an active L" commercial/industrial property, with nearby land used for commercial, industrial, and residential purposes. Commercial properties are located adjacent to the Site to the north and to the south beyond an open field. Residential properties are located to the east across South `r Airport Way, and an open field is west of the Site. The bakery building occupies the majority of the Site, and asphalt and/or concrete pavement surround the building. �. Potentially -complete exposure pathways and receptors have been identified for the Site, with the following criteria: L. • A source and mechanism of chemical release; �, • One or more retention or transport media (e.g., soil, groundwater, soil vapor, air, or surface water); • A point of potential contact with the impacted medium (referred to as the exposure point); and ,� • An exposure route at the point of contact (e.g., inhalation, ingestion, or dermal contact). Figure 8 illustrates a schematic diagram of the site conceptual model, and Figure 9 shows the '- exposure pathway flowchart. Site-specific, potentially -complete exposure pathways and potential receptors are depicted on the figures, and are summarized as follows: • Dermal contact or incidental ingestion of contaminated soil through excavation (onsite residential, commercial, or industrial receptors or construction workers); SL_AIR SCM and RI WP 11