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6.0 POTENTIAL EXPOSURE PATHWAYS AND SENSITIVE RECEPTOR SURVEY An exposure pathway model for the site is presented in Figure 22. The primary source of exposure appears to be spills and leaks related to historical gasoline station operations at the site. Secondary sources for exposure appear to include residual hydrocarbons in subsurface soils and dissolved hydrocarbons in the groundwater. Potential exposure pathways associated with the secondary sources include volatilization to indoor and outdoor air, and the potential for dermal contact and ingestion related to subsurface construction activities at the site. Given the depth to groundwater beneath the site, exposure to hydrocarbons dissolved in the groundwater, through volatilization, contact, or ingestion, appears unlikely. 6.1 Potential On-site Exposure Pathways Exposure potential to the impacted soil and groundwater beneath the site appears limited. Excavation and soil vapor extraction activities have likely removed a significant quantity of petroleum hydrocarbon mass in the shallow subsurface. Exposure to residual hydrocarbons in the soil might come through inhalation of compounds volatilized to indoor or outdoor air. The ground surface of the site is paved with concrete and asphalt. These paving materials are not impervious to soil vapors, but the potential exposure risk associated with volatilization of petroleum hydrocarbon vapors to indoor or outdoor air is unlikely to represent an exposure risk. Normal surface air movement (wind, etc.) is likely to dilute and remove impacted soil vapors • from the site before concentrations reach risk levels. Dissolved petroleum hydrocarbons are present in groundwater beneath the site. Based on the analytical data collected from borings CPT-I, CPT-8, and CPT-10 in 2001, and results of the well VEW-2 samples, the dissolved hydrocarbon plume extends beneath the warehouse building. Given the depth to groundwater beneath the site, and that the building is underlain by a concrete slab, volatilized hydrocarbons from groundwater appear unlikely to accumulate within the warehouse building at concentrations necessary to pose an exposure risk. There is no direct route to groundwater exposure (i.e. a water supply well) at the site. 6.2 Potential Off-site Receptors -Water Supply Wells Two surveys of water supply wells in the vicinity have been performed. EMCON identified six water supply wells located within a 2,000-foot radius of the site (July 1997 Site Closure Report). A consultant for the Del Monte Plant 33 on Filbert Street (located approximately 3,000-feet southeast of the former Apache Plastics facility) identified two water supply wells located within 2,000 feet of the former Apache Plastics facility. Available well information, and a figure illustrating the locations of these wells, is included in Appendix K. The locations and operational status of the wells identified in these surveys have generally not been verified. EMCON Survey: Two wells were identified within 500 feet of the site by the EMCON survey; an industrial supply well approximately 300 feet west-southwest of the subject property (EMCON map ID #4), and a well of unknown usage situated approximately 450 to 500 feet east K,\ppache Plastics\ReportsNapaehe-scm-assessmcnl report2006.doc Page 16 5TRA TU5