Dames & Moore, 1999 - USDA Forest Service

to the extrapolation to low hardnesses of bioassay data from the U.S. €PA Research Laboratory at Duluth
where the hardness is approximately 45 mg CaCOA. However, review of the literature concerning the
toxicity of PCOCs to trout shows that they are able to swive and reproduce in considerably higher
concentrations than would be expected based upon the benchmarks given above. Recent reports from the
Clark Fork Superfund Site near Butte, Montana, reveal that the water quality criteria mag substantially
overpredict toxicity at lower water hardnesses (ARCO, 1996).
The criteria include data for species of animals not found in Railroad Creek. Furthermore, there are many
studies of cadmium, copper, lead, and zinc toxicity to salrnonid fishes conducted at low water hardness
(Table 7.2.3-18) which are more appropriate for Railroad Creek fish species and water conditions. As a
rule, the Salmonidae are generally considered to be the most sensitive family of fish to metals (Spry et al..
1981). These Toxicity Reference Values (TRVs) include both acute and chronic endpoints and full life
cycle maximum acceptable toxicant concentration (MATC) values. The mean of the tish bioassay data for
each metal was considered to provide a weight of evidence that higher concentrations of metals can be
tolerated by salmonid fishes in very soft waters. Because arsenic, mercury, and nickel did not exceed the
screening criteria, no site-specific TRVs were developed for these metals.
The chronic value for iron used in this risk assessment (1300 pg/L) is also different from the national
NAWQC (1000 pg/L). This is because the federal criteria was established on the basis of a 2 1-day Daphnia
magno bioassay using acid mine drainage. This is not a currently accepted method of establishing
NAWQC, and daphnids are not found in flowing waters such as Railroad Creek. Therefore, for the
purposes of this risk assessment, the lowest value from a rainbow trout embryo-larval bioassay (1300 p a)
was used as the TRV (ORNL, 1996).
These chronic values are at least an order of magnitude greater than the federal criteria modeled benchmark
values listed in Table 7.2.3-1A. Since trout are the major resource to be protected in Railroad Creek, the
values in Table 7.2.3-18 and the chronic value NOEC for copper (i.e., 2.3 pg/L) were used as TRVs to
evaluate risk to fish.
Sediment
In those portions of Railroad Creek where sediments or flocculent have accumulated, toxicity to benthic
invertebrates may be judged by comparison with sediment quality guidance values. Chemicals undetected or
found in only trace amounts in the water column can accumulate to relatively high levels in the pore-water
between sediment particles.
Sediment concentrations were screened relative to appropriate benchmarks (Table 7.2.3-2A). Among
available benchmarks are the marifle and estuarine sediment quality guidance values of Long et al. (1995).
the freshwater guidelines of the Ontario Ministry of the Environment (Persaud et al., 1993), and the
Washington State (Ecology, 1997) guidelines for freshwater sediments. Because the marine and estuarine
guidelines (Long et al., 1995) are baied on a much larger database than the freshwater guidelines, the
potential sediment toxicity of Railroad Creek was assessed using these values.
For Long et al. (1995), the effects range-low (ER-L) is defined as the lower 10th percentile and the effects
range-median (ER-M) as the 50th percentile (median) of the chemical concentration data set. Based on a
"preponderance of evidence," the ER-L and ER-M values define three concentration ranges that were (1)
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17693-005619Uuly 21. 1999,5:16 PMDRAFT FINAL RI REPORT