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6 0 EXPOSURE PATHWAYS AND RECEPTOR SURVEY <br /> An exposure pathway model for the site is presented in Figure 7 The primary source of <br /> exposure to petroleum hydrocarbons at this site appears to have been spills and leaks related to <br />' historical fueling operations at the site All USTs and fuel delivery systems have been removed, <br /> and this source of exposure removed Secondary sources for exposure appear to include residual <br /> hydrocarbons in subsurface soils and dissolved hydrocarbons in the groundwater Potential <br />' exposure pathways associated with the secondary sources include dermal contact and ingestion <br /> related to subsurface construction activities and inhalation due to volatilization Given the depth <br /> to groundwater beneath the site and the lack of groundwater extraction at the site, exposure to <br />' hydrocarbons dissolved in the groundwater, through volatilization, contact, or ingestion, appears <br /> unlikely <br /> 61 Potential On-site Exposure Pathways <br /> 6 1 1 Subsurface Soils <br />' Petroleum hydrocarbon-impact in subsurface soils appears to have been removed by excavation <br /> and SVE Given the very low concentrations of hydrocarbons reported from confirmation soil <br />' boring B-17, dermal or ingestion exposure from hydrocarbons in soil appears unlikely <br /> 612 Volatilization <br />' Inhalation exposure to volatilized hydrocarbons appears unlikely Volatilization from the very <br /> small amount of impact identified by boring B-17 will be insignificant, and hydrocarbons were <br /> not reported in SVE influent samples when system operations were terminated The ground <br /> surface of the site is paved with concrete and asphalt While these paving materials are not <br /> impervious to soil vapors, they are likely to represent a significant barrier to what little vapor is <br />' likely to be present The only remaining structure at the site is not currently utilized, and given <br /> its condition, is not likely to allow accumulation of vapors within There are no other structures <br /> or topography at the site that might limit airflow and allow the accumulation of vapors <br /> 613 Groundwater <br />' Low concentrations of dissolved petroleum hydrocarbons are present in groundwater beneath the <br /> site These low dissolved concentrations and the significant depth to groundwater beneath the <br /> site suggest volatilization from groundwater will be insignificant Inhalation exposure risk from <br />' this secondary source appears to be unlikely There are no water supply wells at the site, and <br /> California Water Service serves the site Exposure risk via ingestion or dermal contact appears <br /> unlikely <br /> 1 62 Potential Off-site Receptors - Water Supply Wells <br /> The only potential off-site receptors appear to be water supply wells in the area The depth of <br />' the groundwater beneath surface grade suggests it is unlikely that the dissolved hydrocarbons <br /> will impact surface waters Analytical data collected to date suggests that the dissolved plume is <br /> K\Teichert\Stockton-iO3\Reports\scm 04-2006 doe Page 11 STRATUS <br />