Dames & Moore, 1999 - USDA Forest Service

Trout
An intermediate potential risk for adverse effects (HQ>l but 400) to trout may be present
due to copper concentrations in surface water in Railroad Creek adjacent to the site under
both the worst-case and reasonable exposure scenarios. A small potential risk for adverse
effects, downstream of the Site, due to copper was identified using the mainstream Railroad
Creek water quality data under both the worst-case and reasonable exposure scenarios.
• Trout may possibly be at risk due to iron concentrations in surface water adjacent. to the site
under a worst-case scenario; however, no risk was. identified using the median mainstream
data.
Benthic Invertebrates
The combined results of the ERA and ecological survey suggest that reduced trout
populations adjacent to the Site near RC-9 to downstream of tailings pile 3 appear to be
primarily attributable to the lack of suitable habitat or food items due to the presence of
flocculent, although some 'potential risk for. adverse effects due, to dissolved metals was
noted.
HQs were less than or equal to 1 for all other metals for trout.
A metals toxicity risk to benthic macroinveitebrates under the worst-case and revonable
exposurescenarios in surface water of Railroad Creek does not exist.
A small potential risk of adverse effects may be present for benthic macroinvertebrates due
to metal concentrations (copper, iron, manganese, and zinc) in sediment fiom Railroad
Creek adjacent to and downstream of the site (HQs ranged fiom 1.0 to 3.0). Exceedances
of sediment quality guidelines have been shown to be unreliable predictors of toxic
conditions. Bioassays conducted by Ecology (1997) did not show toxicity dui to metals
concentrations in Railroad Creek sediment.
An intermediate potential risk of adverse effects to benthic macroinvertebrates may be
present due to metal concentrations (arsenic, cadmium, copper, iron, silver, and zinc) in
flocculent adjacent to the site in Railroad Creek. It should be noted that the bioavailability
and toxicity of metals in flocculent is unknown. Data from other mine sites suggest that
flocculent may not be toxic. The benthic macroinvertebrate community assessment
conducted during the RI within ,Railroad Creek, both upstream and downstream of site
influences, exhibited a wide range of conditions. The presence of flocculent on and in the
substrate in Railroad Creek fiom the lower portion of station RC-9 to downstream stations
(except RC-3) has influenced the substrate by infilling the interstitial spaces and coating the
surface of substrate which generally limits the establishment of periphyton. However, three
new genera of pollution sensitive organisms are present at RC-7 and RC-9 and are assumed
to be present due to the alteration in habitat. The benthic community at station RC-3
indicates recovering conditions. The combined results of the ERA and the 'Railroad Creek
benthic community evaluation indicate that the reduced benthic community adjacent to the
Site near RC-9 to downstream of tailings pile 3 (RC-7) is predominately attributable to the
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17693405-019Uuly 28, 1999;12:16 PM;D~F~ FWAL RI REPORT ES- 1 1