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GeoInsighter Winter 2002 Newsletter THE RISK IN RISK-BASED CLEANUP STANDARDS Return to the Newsletter Index The environmental cleanup standards that responsible parties are required to cleanup to are derived during the To address uncertainty in predicting future site uses, risk characterization procedures commonly use health-protective and conservative assumptions, such as overestimating the magnitude of exposure to impacted media. For example, in situations where adults or children live near a site containing impacted soil, it is commonly assumed in the risk characterization that there is routine contact and ingestion of between 50 and 100 milligrams of impacted soil per day for 30 years. However, in many instances, a barrier restricts exposure to the soil and/or the duration is not as long as assumed. Another uncertainty factor in risk characterization stems from the extrapolation of human toxicity of chemicals from laboratory studies using animals. To ensure protection of human health and safety, standard risk characterization practice and regulation require that toxicity values reflect “worst case” results. For example, it is assumed that humans are more sensitive to chemicals than the most sensitive laboratory animals tested. In addition, a safety factor between 1,000 and 100,000 is incorporated into the toxicity values for humans. Therefore, actual health risks are likely to be less than what is estimated in the risk characterization. The derivation of exposure point concentrations (i.e., the concentration of the chemicals of concern in soil, ground water, or air that humans could be exposed to) is the third uncertainty factor in the risk characterization process. There are a number of site and risk characterization approaches either required by regulation or presented in regulatory guidance or policy that result in conservatively high exposure concentrations. One example deals with sampling bias that produces higher concentrations than what humans may be exposed to. Examples of sampling bias include soil sampling in areas where higher concentrations are expected or where higher headspace field screening results are observed. Another example deals with the use of current ground water quality data and assuming that the current concentrations will be constant over the exposure duration (typically 25 to 30 years). However, in the absence of a contaminant source, chemicals dissolved in ground water will naturally attenuate over time, resulting in lower exposure concentrations over the exposure duration. In summary, the conservative assumptions associated with risk characterization uncertainties are cumulative, generally resulting in the derivation of conservative health risks to ensure the protection of public health and safety. Richard J. Wozmak, P.E., P.H., L.S.P.,
L.E.P. Return to the Newsletter
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risk characterization process. Many types of uncertainty enter into risk characterization when deriving carcinogenic and non-carcinogenic health risks. These uncertainties come into play when estimating future site use scenarios, chemical toxicity, and exposure concentrations for constituents present in site environmental media. To account for these uncertainties, standard risk characterization practices are generally conservative and adopt safety factors to minimize the risk of deriving unsafe cleanup standards.