Dames & Moore, 1999 - USDA Forest Service

Although certain benthic invertebrates burrow into soft sediments in some environments. the high currents
and hard surfaces on Railroad Creek assure that the majority of benthic species are attached to hard surfaces
and are only exposed to surface water metal concentrations. Furthermore. although some benthic
invertebrates may ingest metal particulates or flocculent with their diet of periphyton, there is no exposure
or toxicity data by which to judge the severity of such exposures. However, because of the oxygen
requirements of both invertebrates and fish, and the high rates of ventilation k opposed to low rates of gut
peristalsis, the aquatic portion of metal body burdens are generally thought to be the more important route of
exposure except in waters of very low metals concentrations (Handy, 1992; Spry et al., 198 1 ; Hodson et al..
1980). Therefore, the risk to benthic invertebrates was estimated by comparison with site-specific water
concentrations and toxicity values for metals concentrations (Table 7.2.3-2B) causing adverse effects on
benthic invertebrates such as are found in Railroad Creek. In addition, however, sediment data collected by
USBM (1 993, and Ecology (1997) as well as flocculent samples collected by Dames % Moore (1 998) in
slow moving reaches of Railroad Creek, were compared to sediment quality guideline values (Table 7.7.3-
2A). This analysis was not separated from evaluation of the hyporheic zone because it is undefined in
Railroad Creek and because the same insect larvae are found in the hyporheic zone as were evaluated for the
surface waters.
Because none of the metals in Copper Creek exceeded these receptor-specific benchmarks for either benthic
insects or trout, no further analysis of risk was conducted for this stream. In general, metals levels in
Copper Creek were the same as the reference stations at Ten-Mile Creek, Bridge Creek, Company Creek,
and the South Fork of Agnes Creek.
American Di~wr
Dippers are insectivores that feed in riffles on benthic macroinvertebrates such as caddis fly and stonefly
nymphs. No measurements were made of the concentrations of metals in 'benthic invertebrates at the site.
Kemble et al. (1992) reported concentrations of cadmium, copper, lead, and zinc in pore-water and benthic
macroinvenebrates collected from the Clark Fork River (CFR), near Butte Montana. Cain et al. (1992)
reported that these animals were mainly caddisflies and stoneflies, animals expected to be fed upon by
dippers and common in Railpad Creek. To estimate the body burdens of cadmium. copper, lead, and zinc
in Railroad Creek invertebrates, a simple ratio of the UCL of Railroad Creek water concentrations divided
by the closest concentration of CFR pore-water was multiplied by the CFR body burden (Table 7.2.3-5;
7.2.3-6). .There are no data available for iron concentrations in benthic invertebrates.
Exposure to birds was estimated using mass-dependent algorithms (ERA, 1993). The water ingestion rate
(W) in birds was estimated as:
where
W (Ud) = 0.059 x (kg Body
0.67 = relationship between body mass and water requirements
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17693405-019Uuly 27, 1999;5:16 PMDRAFT FINAL RI REPORT