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McDowell&Davis Towing <br /> Geoprobe Soil Boring&Revised Risk <br /> Assessment and Conceptual Site Model Report <br /> Page: 6 <br /> rr <br /> Calculated parameters include site-specific exposure concentrations, average daily <br /> uptake, baseline risk and risk based cleanup levels. Fate and transport analytical <br /> models are used to evaluate site-specific soil, groundwater, and air exposure <br /> pathways. <br /> 4.2 Receptors and Potential Pathways <br /> Potential receptors were identified as ingestion, dermal exposure, contaminated <br /> groundwater ingestion, and vapor inhalation. Potential pathways for exposure <br /> including onsite and offsite ingestion and dermal exposure to contaminated surface <br /> soils; onsite and offsite exposure to contaminate vapors sourced from surface <br /> contaminated soil, subsurface contaminated soil, and contaminated groundwater, and <br /> onsite and offsite ingestion of contaminated groundwater. <br /> The excavation and off site disposal of all surface and shallow contaminated soil has <br /> eliminated the potential exposures through dermal exposure and ingestion of surface <br /> contaminated'soil and inhalation of vapors from contaminated surface soil. Drinking <br /> water for the McDowell and Davis Towing facility is supplied by the City of Escalon <br /> from offsite production wells, which removes the possibility of onsite ingestion of <br /> contaminated groundwater. <br /> Potential receptors and pathways identified in the previous risk assessment are listed <br /> two -,WW below: <br /> below: <br /> 1) Onsite outdoor inhalation of contaminant vapor sourced from subsurface <br /> contaminated soil <br /> 2) Onsite outdoor inhalation of contaminant vapor sourced from contaminated <br /> groundwater <br /> 3) Offsite outdoor inhalation of contaminant vapor sourced from subsurface <br /> contaminated soil <br /> 4) Offsite outdoor inhalation of contaminant vapor sourced from contaminated <br /> groundwater <br /> 5) Onsite indoor inhalation of contaminant vapor sourced from subsurface <br /> contaminated soil <br /> 6) Onsite indoor inhalation of contaminant vapor sourced from contaminated <br /> groundwater <br /> 7) Offsite ingestion of contaminated groundwater. <br /> w.. <br /> The risk assessment identified onsite indoor inhalation of benzene and xylene vapors <br /> sourced from subsurface contaminated soil as the only potential exposure. The model <br /> �. was revised with the reduced estimate of contaminate volume and run to reevaluate <br /> the potential indoor air inhalation of benzene and xylene vapors. The standard <br /> parameters for commercial indoor air exposures are based on a postulated inhalation <br /> •• of 20 cubic meters /day for 250 days a year for 25 years by a 70 kg individual. The <br /> model assumes a cross media transfer, organic vapor flux from the impacted soil and <br /> `■. <br /> V <br />