Dames & Moore, 1999 - USDA Forest Service

• 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.
• The combined results of the ERA and ecological survey suggest that reduced trout
population adjacent to the Site near RC-9 to downstream of tailings pile 3 is more
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 identified.
a HQs were less than or equal to 1 for all other metals for trout.
Benthic Invertebrates
a A metals toxicity risk to benthic invertebrates under the worst-case and reasonable
exposure scenarios in surface water of Railroad Creek does not exist.
• A small potential risk of adverse effects may be present for benthic invertebrates due to
metal concentrations (copper, iron, manganese, and zinc) in sediment from Railroad Creek
adjacent to and downstream of the site (HQs ranged from 1.0 to 3.0). Exceedances of
sediment quality guidelines have been shown to be unreliable predictors of toxic
conditions. However, bioassays conducted by Ecology (1997) did not show toxicity due to
metals concentrations in Railroad Creek sediment.
An intermediate potential risk of adverse effects to benthic invertebrates 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 from 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 benthic community
evaluation suggest that the reduced benthic community adjacent to the Site near RC-9 to
downstream of tailings pile 2 (RC-7) is more attributable to the lack of suitable habitat due
to the presence of flocculent, although some potential risk for adverse effects from metal
flocculent concentrations was identified.
• Under a reasonable scenario condition, there is no risk due to metals toxicity to the birds or
mammals associated with aquatic habitat near the site.
7.2.6.2 Terrestrial Exposure Pathway and Receptors of Concern
Plants may experience toxicity from cadmium, copper, lead, and zinc in Holden Village
surface soil and in the surface soils and subsurface soils of tailings piles 1, 2 and 3, the
lagoon and the maintenance yard; however, when compared to soil metals concentrations at
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