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Steven Sasson -4- February 5, 1996 of hydraulic fluid in the soil was used as the representative concentration TPH as hydraulic fluid was detected during the soil sampling events (CRC 1994, 1995) 2.1.2 Exposure Assessment The exposure assessment step is conducted to estimate the magnitude of actual and/or potential human exposures, the frequency and duration of these exposures, and the pathways by which humans are potentially exposed (USEPA 1989) In the exposure assessment, reasonable maximum estimates of exposure are developed for both current and future land-use assumptions Conducting an exposure assessment involves analyzing releases of chemicals, identifying exposed populations, identifying potential pathways of exposure, estimating exposure point concentrations for specific pathways, and estimating chemical intakes for specific pathways The results of this assessment present pathway-specific intakes for current and future exposure to hydraulic fluid At this site, hydraulic fluid contamination was suspected from a leak in an elevator piston housing, which was buned in an uncased borehole at a depth of 13 feet Because of the depth of the contamination (i e , the chemical was not present at 0 to 10 feet below ground surface), it is not likely that humans would have direct contact with the hydraulic fluid However, to be consistent with the PEA Guidance Manual and to produce a conservative estimate of risk, it is assumed that humans will have direct contact with the soil There is also the potential for the chemicals to volatilize and for humans to inhale the vapors from the chemicals in the soil It is, therefore, assumed that the following exposure routes for soil are applicable to this assessment* • Inhalation Volatile Organic Compounds (VOCs) from emissions from soil • Ingestion Hydraulic fluid in soil • Dermal Absorption Direct contact with hydraulic fluid in soil 2.1.3 Exposure Point Concentrations The maximum concentration of TPH as hydraulic fluid in the soil (1,600 milligrams per kilogram of soil (mg/kg) was used as the exposure point concentration To calculate the concentration of VOCs in the air from emissions from the hydraulic fluid in the soil, the methodology presented in the PEA Guidance Manual was used (DTSC 1994) The estimation of air concentration for VOCs uses the equation Ca = Ei / 99 Where 40 Ca -- Ambient air concentration, milligrams/meter cubed (mg/m3) Ei — Total emission rate for compound i, milligrams/second (mg/s)