Dames & Moore, 1999 - USDA Forest Service

were no more toxic than sediments collected from their reference location upstream of the mine site. They
also reported there was no relationship between toxicity and metal concentration.
Sediment sampling was performed at Lucerne Bar as part of the RI field effort. The results were previously
discussed in Section 5.0. With the exception of zinc concentrations at one sample location, metal levels in
sediments were below Ecology's FSQV. The zinc levels at this location do not appear to represent adverse
effects; however, additional sediment sampling will be performed to define the metal chemical
concentrations at this one location.
Benthic Invertebrates- Flocculent
In addition to the benthic macroinvertebrates that are attached to hard substrates, or sediments, there may be
benthic invertebrates that are exposed to flocculents near the portal drainages and downstream. Samples
were collected near the portal drainages in the belief that these areas would contain the highest
concentrations of precipitated metals. Two of the samples were measured wet (RC-2 and RC-5) and one
sample was measured dry. The median values of these three measurements in flocculent were found in the
sample from RC-5. HQs greater than 1.0 are shown in bold in Table 7.2.4-2D.
As with sediment samples, exceedance of the ER-L means that flocculents may "occasionally" be toxic.
Therefore, it may not be appropriate to use these exceedances as evidence of potential adverse effects to the
benthic communities at the sites where data were collected or for Railroad Creek in general. In fact, data
reported elsewhere in this report shows that metal-sensitive insect nymphs are present in the same areas as
the flocculent was collected. Comparison of flocculent concentrations to sediment quality guideline values
may not be appropriate because flocculent is not sediment. For example, its natural state, is a dispersion of
colloidal metals which contain much more water than solid, while sediments contain much more solid than
water. Furthermore, the bioavailability and toxicity of the metals in flocculent is unknown.
Because of the uncertainty associated with interpretation of sediment quality guidelines, it may be more
appropriate to assess the potential toxicity of flocculents by exceedance of the ER-M, those concentration
"Frequently" associated with toxicity. When this was done, exceedances were only found for arsenic,
copper, iron, silver and zinc at locations adjacent to the mining site, and HQs range from 1.8 to 3.1.
American Diuuer
Hazard quotients for American dipper (Table 7.2.4-5) were calculated by dividing the doses estimated in
Table 7.2.3-7 by the TRVs in Table 7.2.3-4A. The default assumptions were:
dippers fed only on aquatic insects from the South Bank of Railroad Creek
dippers drink only the UCL concentrations from Railroad Creek
the modeled insect metal concentrations were accurate for Railroad Creek
From Table 7.2.4-5, it is apparent that American dipper is not at risk even under the worst case exposure
assumptions. Therefore, there is no need to conduct further analyses of risk to this ROC.
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17693-005-01 Wuly 27.1999:5:16 PMDRMT FINAL RI REPORT