Dames & Moore, 1999 - USDA Forest Service

7.0 BASELINE RISK ASSESSMENT
Both a Baseline Human Health Risk Assessment (HHRA) and Baseline Ecological Risk Assessment (ERA)
were prepared for the Holden Mine Site and nearby Holden Village in Chelan County. Washington (Figures
7.0-1 through 7.0-3 and Table 7.0-1). The overall approach and methodology for evaluating the risks
associated with the Site are discussed below.
7.1 HUMAN HEALTH RISK ASSESSMENT
7.1.1 Methodology
The intent of the HHRA is to evaluate the potential for threats to human health based on available
information collected by the USGS, USFS, Ecology, and Dames & Moore.
A systematic evaluation of the potential risks to human health was conducted in accordance with guidelines
outlined in the following Ecology and U.S. Environmental Protection Agency (USEPA) documents:
Washington State Model Toxics Control Act-Cleanup (WAC 173-340); Model Toxics Control Act Cleanup
Levels and Risk Calculations (CLARC I4 Update (Ecology, 1996); Statistical Guidance for Ecologv Site
Managers (Ecology, 1992); Supplement to Statistical Guidance for Ecology Site Managers (Ecology. 1993):
Risk Assessment Guidance for Superfimd, Volume I, Human Health Evaluation Manual (Part A) (USEPA.
1989) and Part B (USEPA, 1991'b); W ce of Solid Waste and Emergency Response (OSWERJ Directive
9285.6-03, Supplemental Guidance: Standard Default Exposure Factors (USEPA, 1 99 1 a); Guidance for
Data Usability in Risk Assessment (USEPA, 1992b); and Soil Screening Guidance: Technical Background
Document (USEPA, 1996).
The human health risk assessment process typically involves five basic elements:
1. Data Review and Evaluation. Available data were reviewed to characterize the Site and
its associated constituents, define the nature and magnitude of constituent releases to
environmental media (soil, air and water), and identify site-related indicator hazardous
substances (IHSs).
2. . Exposure Assessment. The exposure assessment defines the amount frequency, duration,
and routes of receptor exposure to site-related IHSs. The exposure assessment considers
both current and likely future site uses, and is based on complete exposure pathways to
actual or probable receptors (i.e., the people that could come in contact with site-related
IHSs). Exposure scenarios are summarized in the Exposure Pathways Model. Exposure
point concentrations representative of upper-bound exposure conditions in each affected
medium are also estimated in the exposure assessment. In this baseline risk assessment, the
exposure assessment is conducted in the screening level human health assessment and then
refined in the site-specific HHRA.
3. Toxicity Assessment. The toxicity assessment serves to (I) identify the nature and degree
of toxicity of each IHS, and (2) characterize the dose-response relationship (the relationship
between magnitude of exposure and magnitude of adverse health effects) for each IHS.
Two kinds of effects are recognized: (1) non-carcinogenic effects, and (2) carcinogenic
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