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Steven Sasson -5- February 5, 1996 Ei 1 6 x 105 x Di x Hc/Kd x 0 (Dix 0 023 0 284 + 0 046 x KdlHc) Di = Diffusivity in air for compound i, centimeters squared per second (0 088 cm'/sec) He = Henry's Law constant, atmospheres-cubic meter per mole (5 43 x 10- 3 atm-m3/mole) Kd -- Soil-water partition coefficient, cubic centimeters per gram (1 3 cm3/g) C1 = Bulk soil concentration of contaminant i, (chemical concentration in soil, mg/kg, x (10' kg/mg)) (1600 mg/kg x 10-6mg/kg) In the absence of physical/chemical properties for hydraulic fluid, a surrogate chemical was used to calculate the concentration of volatile emissions in air The surrogate chosen was benzene The use of benzene is conservative because it is more volatile than any component in hydraulic fluid Although benzene is not a component of hydraulic fluid, it is typically used as an indicator compound for TPH Using the previous equations, concentration of hydraulic fluid vapors in air was estimated at 0 09 mglm3 2.1.3 Dose-Response Assessment The purpose of the dose-response or toxicity assessment is to weigh available evidence regarding the potential for particular agents or chemicals to cause adverse effects in exposed individuals (weight-of-evidence), and to quantitatively characterize, where possible, the relationship between the extent of exposure to an agent or chemical and the increased likelihood and/or seventy of adverse effects (dose-response assessment) Chemicals are usually evaluated for their potential health effects in two categories, carcinogenic and noncarcmogeruc Different methods are used to estimate risk associated with health effects in these two categories Some chemicals which produce carcinogenic effects may or may not also be associated with noncarcinogenic effects True noncarcinogens are not associated with cancer responses Most regulatory agencies consider carcinogens to pose a risk for cancer at all exposure levels (n e , a "no-threshold" assumption), that is, any increase in dose is associated with an increase in the probability of developing cancer In contrast, noncarcinogens generally are thought to produce adverse health effects only when some minimum exposure level is reached (i e , a threshold dose) Several sources, corresponding to the state of California's preferred hierarchy (Cal/EPA 1994b) for cancer slope factors and reference doses were consulted for use in this report I