Dames & Moore, 1999 - USDA Forest Service

7.1.1.2 Site-Specific Human Health Risk Assessment
The site-specific HHRA was conducted for those constituents and exposure pathways which significantly
contributed to the risk at the site as determined in the screening level human health assessment. The
methodology for the site-specific HHRA was performed in the following steps:
Characterize the relevant exposure pathways
Develop exposure concentrations based on statistical evaluation of the data
Characterize the toxicity of the IHSs
Develop site-specific cleanup levels
Characterize risks associated with the site
Discuss uncertainties in the risk characterization
Each step of the site-specific HHRA is discussed in detail in Section 7.1.4.
7.1.2 Data Evaluation
The purpose of the data evaluation section is to summarize the types of data utilized in the risk assessment
and to evaluate specific data sets as they pertain to the selection of indicator hazardous substances (IHS).
7.1.2.1 Source Characterization by Media
Holden Mine was a copper, zinc, gold and silver mine located to the west of Lake Chelan in the Railroad
Creek watershed of Chelan County, Washington. The mine operated from 1938 to 1957 and generated
approximately 10 million tons of tailings materials. Approximately 8.5 million tons of the tailings were
deposited in three impoundments constructed adjacent to Railroad Creek (i.e., tailings piles 1.2 and 3). The
remainder of the material was backfilled in the underground mine workings. The USFS has completed a
number of site reclamation efforts, including the covering of the tailings piles with gravel to mitigate dust
emissions, the installation of surface water interceptor swales, bank protection for Railroad and Copper
Creek, and the revegetation of the surface of the tailings piles. Additional details on the mine and its
environs can be found in Sections 1,2 and 4.
The Site has been extensively studied by others since mine and mill closure in 1957. The investigations
have included sampling and analytical testing of surface water, sediments, groundwater, soil, tailings. seeps,
mine portal drainage, air, and aquatic macroinvertebrates and fish. The primary focus of the studies was to
assess the impacts of the tailings piles and mine discharge on the above-mentioned media. Detailed tables
containing sample results for recent and historic samples can be found in Section 5. All 1997 and 1998 data
collected by Dames & Moore were validated as discussed in Section 5. Data which has been used for the
risk assessment is discussed below by media, and includes 1997 and 1998 Dames & Moore data and, in
some cases, historical data' collected by others from 1991 to 1997. Data tables for the risk assessment are
included in Tables 7.1-A through 7.1 -K of this risk assessment.
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17693-005419Vuly 27.1999.5:16 PMlDIlAFT FINAL RI REPORT