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j Human Health Risk Assessment <br /> Former Mobil Oil Bulk Plant 04-343 <br /> 540 East Grant Line Road <br /> Tracy, California <br /> project number, well number, sample date, and sampler's initials. TL-, samples will be kept on <br /> ' ice or refrigerated g prior to Laboratory analysis. <br /> ' 1.3.3.2 Human Health Risk Assessment <br /> Risk assessment has been defined as "the characterization of the potential adverse health effects <br /> of human exposures to environmental hazards" (NRC, 1983). A component of the risk <br /> ' assessment is quantifying the extent to which a group of people has bff.n, or may be, exposed <br /> to a chemical. The magnitude of the potential exposure is evaluated in relation to the type and <br /> degree of hazard posed by the chemical. Potential risks resulting from carcinogenic and <br /> noncarcinogenic chemicals are evaluated separately in the risk assessment process. The equation <br /> summarizing the principal of risk assessment is: <br /> ' Toxicity x Exposure = Risk <br /> ' Where toxicity is a measure of the inherent ability of a chemical to c.; use harm, and exposure <br /> is the measure of the dose that may be received by a person. Risk is the probability of injury, <br /> disease, or death under specific circumstances. It may be expressed in quantitative terms, taking <br /> values from zero (certainty that harm will not occur) to one (certaint; that harm will occur). <br /> ' All human activities carry some degree of risk. Many risks are known with a relatively high <br /> degree of accuracy, because data have been collected on their historical occurrence. Table 1-4 <br /> lists the risks of some common activities. <br /> All substances, even those that we consume in high amounts every day, can be made to produce <br /> ' a toxic response under some conditions of exposure. In this sense, all substances are potentially <br /> toxic. The important question is not simply that of toxicity, but rather that of risk. In other <br /> ' words, what is the probability that the toxic properties of a chemical will be realized under <br /> actual or anticipated conditions of human exposure. The completion of a comprehensive human <br /> health risk assessment can provide answers to this question and, in addition, be used in selecting <br /> approaches to reduce unacceptable risks to allowable levels. <br /> 30-0136-11 <br />