Dames & Moore, 1999 - USDA Forest Service

concentration that contains the bioavailable metal that causes toxicity. Furthermore, in high gradient fast
moving stream such as Railroad Creek and Copper Creek, very little sediment accumulates. and the
macroinvertebrates that serve as trout and dipper food are largely attached to hard substrates. Therefore, the
toxicity to benthic invertebrates (largely insect nymphs) in Railroad Creek is more properly estimated based
upon aqueous exposures rather than sediment exposures.
Commonly used bioassay animals such as Daphnia magna and Ceriodaphnia dubia are not found in
flowing waters such as Railroad Creek, but are always included in the calculation of water quality criteria.
Therefore, a number of studies with benthic invertebrates similar to those found in Railroad Creek (i.e..
stonefly, caddisfly, mayfly, damselfly) were reviewed and compiled (Table 7.2.3-28). These data, used
subsequently as tier ll toxicity values, were gathered from experiments for 96 hours (acute) or greater
(chronic), and include several no observed effect concentrations (NOECs). Where greater than (">") values
were reported these were ignored and the values used were unchanged. Where ranges were reported, both
low and high estimates were used. These data were considered to provide a weight of evidence that higher
concentrations of metals can be tolerated by benthic macroinvertebrates than is apparent in the water quality
criteria. Since most of the benthic invertebrates found in Railroad Creek are insect nymphs that attach to
hard substrates, the benthic invertebrate study values in Table 7.2.3-28 were used to evaluate risk to aquatic
invertebrates.
Terrestrial Habitats
- Soils
Neither'the USEPA nor the State of Washington have established ecologically-based screening levels for
soils. Therefore, the Oak Ridge National Laboratory toxicological benchmarks for plants (Efioymson et al.,
1997) and earthworms (Will and Suter, 1997) were used to screen soils. In addition, because cyanide was
not evaluated by ORNL, this value is the target value designated by the Dutch Minisby of Soil Protection
(1996). These are used in conjunction with the upper 90th percentile of background soils data compiled by
Ecology (1994) for the Yakima Basin, which includes Chelan County, and 1998 background values
collected near the site (Dames & Moore, 1997). If the background was higher than the toxicity benchmark,
the background concentration became the screening value. If the site data exceeded the natural background
values as well as the toxicity benchmark values for plants or earthworms, the hazard analysis proceeded.
Metals were eliminated as COCs if: (1) the background data exceeded the site data, (2) there were no
phytotoxicity or earthworm data, or (3) there were no background data by which to judge if the site data was
greater than background. In addition, chromium was eliminated because there were no cr3 toxicity values,
and this is the major form available in the natural environment. Silver was eliminated because there is no
primary toxicity value available (Efroymson et al. 1997; Will and Sule 1995).
The soil screening values are shown in Table 7.2.3-3A. Comparison of the UCL of the site data fiom Table
7.2.2-1E with the screening criteria presented in Table 7.2.3-3A shows that several metals in soils and
tailings fall below the screening values; therefore, the following metals were not evaluated further:
Soil -aluminum, arsenic, barium, beryllium, iron, manganese, mercury, nickel, selenium,
silver and thallium
Since there is little or no toxicity data for mammals or wildlife exposed to metals potentially found in air-
borne dust, and no Site dust data exists, this potential exposure pathway was not evaluated for risk, although
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17693-005-019Uuly 27. 1999,5:16 PMDRAFT FINAL RI REPORT