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Specifically, identification of complete exposure pathways was based on presence of <br /> 1) a source and mechanism of chemical release, <br /> 2) one or more retention or transport media (e g, soil, groundwater, or air), <br /> ' 3)a point of potential contact with the impacted medium, and <br /> 4)an exposure route at the point of contact (e g, inhalation, ingestion, or dermal contact) <br /> 3 13 1 Onsite Receptors <br /> Based on presence of a paved surface and the estimated depth of impacted soils (16 to 35 ft bgs)at the site, <br /> ' daily site occupants will not be subject to direct exposure(ingestion, dermal contact)to hydrocarbons in <br /> site soils However, as a result of potential cracks in the paved ground surface and/or the building <br /> foundation at the site, potential exposure of site occupants to hydrocarbons in soil may occur through <br /> ' volatilization and emission of vapors to outdoor and indoor air <br /> Based on the depth to groundwater(23 to 48 feet bgs)and the absence of onsite water supply wells, there is <br /> no potential for direct contact with groundwater at the site The sole potential exposure of site occupants to <br /> chemicals in groundwater is through inhalation of volatile emissions to outdoor and indoor air <br /> Completeness of this exposure scenario is once again based on the conservative assumption that cracks <br /> ' may occur in the paved surface and/or the building foundation at the site <br /> As a result of hydrocarbon source removal from soils, the potential for future leaching of chemicals in soils <br /> to groundwater is considered negligible This is corroborated by the sporadic detection and stability of <br /> hydrocarbon concentrations in groundwater underlying the site As a result, exposure pathways associated <br /> with future leaching of soils to groundwater are considered incomplete <br /> ' Although unforeseen, potential construction or maintenance/utility work may occur at the site Should <br /> excavation occur to depths below 16 ft bgs, such activities may result in temporary, direct exposure <br /> ' (ingestion, dermal contact, inhalation of volatiles and particulates)of workers to hydrocarbons in soils <br /> underlying the site Excavation is not likely to occur to depths below the water table, particularly in the <br /> absence of dewatering, hence, direct exposure of construction workers to groundwater was considered an <br /> ' incomplete pathway <br /> Based on the above-mentioned potential complete exposure pathways, the following exposure scenarios <br /> associated with onsite human receptors are considered complete and were evaluated in the RBCA analysis <br /> 1 . Inhalation of volatiles from soil to outdoor air(onsite commercial/industrial receptor), <br /> • Inhalation of volatiles from soil to indoor air (onsite commercial/industrial receptor), <br /> ' . Inhalation of volatiles from groundwater to outdoor air (onsite commercial/industrial receptor), <br /> • Inhalation of volatiles from groundwater to indoor air(onsite commercial/industrial receptor), and <br /> • Ingestion, dermal contact, and inhalation of volatiles and particulates from soil(onsite construction <br /> ' worker) <br /> 3 1 3 2 Offsite Receptors <br /> As previously indicated, water supply wells downgradient of the site are limited to two <br /> agricultural/irrigation wells located approximately 14 mile south-southeast of the site Although the <br /> ' perforated depths for these wells are unknown, they are most likely screened in water-bearing zones deeper <br /> than that impacted beneath the site Nevertheless, as a conservative measure, potential offsite migration of <br /> 7 <br />