Dames & Moore, 1999 - USDA Forest Service

effects. The same constituent may exert both kinds of effects. USEPA has developed
toxicitywiteria for most of the constituents detected at the site.
4. Risk Characterization. ,. In risk characterization, exposure and toxicity data were 0
combined to define site-specific cleanup criteria and estimate the nature and magnitude of
potential risks to defined receptor populations. Non-carcinogenic risks to human receptors
were quantified by the haziud quotient (HQ), the ratio of IHS concentration in site media to
the corresponding non-cancer risk-based level multiplied by the acceptable hazard.
Cumulative hazard is expressed as a hazard index (HI). Carcinogenic risks were quantified
by estimating the excess cancer risks, expressed by the ratio of the IHS concentration to the
cancer risk-based levels multiplied by the acceptable cancer risk.
5. Uncertainty Analysis. Like &y other form of modeling, risk assessment relies on a set of
assumptions and estimates, each of which has some element of uncertainty. The
uncertainty analysis accounts for both variability in and lack of knowledge about measured
and estimated parameters, allowing decision makers to better evaluate risk estimates in the
context of the assumptions and &ta used in the assessment.
This Human Health Baseline Risk Assessment was performed in two stages: 1) screening level human
health assessment, and 2) site-specific human health risk assessment. The purpose of the screening level
human health assessment was to produce a comprehensive conceptual site model in order to select
appropriate IHSs. The site-specific HHRA quantified risks and hazards for those pathways considered
significant.
7.1.1.1 Screening Level Human Health Assessment
The methodology for conducting the screening level human health assessment was applied sequentially, as
follows:
Develop a comprehensive, preliminary conceptual site model for the site
Develop criteria for screening data
Conduct data evaluation
Refine the exposure pathways model
Select IHSs
The results of these steps were used to select significant exposure pathways for the site-specific HHRA.
Each step of the screening human health assessment is discussed in detail in Section 7.1.3.
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17693-0059 I9Uuly 27. 1999:s: 16 PMDRAFT FINAL RI REPORT