Dames & Moore, 1999 - USDA Forest Service

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. I
9.2.7.2 Benthic Invertebrates
a A metals toxicity risk to benthic macroinvertebrates 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 macroinvertebrates 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.
Bioassays conducted by Ecology (1997) did not show toxicity due to metals concentrations in
Railroad Creek sediment.
a 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 fiom 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 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 lack of suitable habitat due to the presence of
flocculent, although some potential risk for adverse effects from metal ' flocculent
concentrations was noted.
• Under a reasonable scenario conditions, there is no risk due to metal toxicity to the birds or
mammals associated with aquatic habitat near the site.
9.2.7.3 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 other
mine sites where plants are successfully growing, only copper concentration in subsurface
soils, the lagoon, and maintenance yard may present a risk of phytotoxicity.
• Earthworms may be at risk from cadrnium,copper, lead andlor zinc in surface and subsurface
soils at Holden Village, tailings piles, dust, lagoon and the maintenance yard under the worst-
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17693-005419Uuly 28.1999;11:34 AMDRAFT FINAL RI REPORT
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