Dames & Moore, 1999 - USDA Forest Service

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Benthic macroinvertebrates and fish populations were reduced in Railroad Creek within the
segment of the stream with iron-oxide staining and flocculent on the substrate. This 0
extended from the northeast comer of tailings pile 1 to station RC-5, located approximately
one-half mile downstream of tailings pile 3.
At approximately 3 miles downstream of the Site (sampling station RC-lo), benthic
macroinvertebrate populations were reduced in comparison to the upstream control stations.
Fish populations at this station were within the range of data collected at both the control
sites outside the watershed and the upstream control sites. Several young fish, which are
generally less resistant to dissolved metals than adult fish, were found at this station.
Fish populations at the mouth of the creek RC-3 were higher than those at the stations
upstream of the Site, but lower than those at the Company Creek control site.
Benthic macroinvertebrate populations near the mouth of Railroad Creek (RC-3) were
reduced in comparison to upstream and control stations but had partially recovered in
comparison to stations closer to the Site.
Of the benthic macroinvertebrate species observed in Railroad Creek, "filter feeders" are
present throughout Railroad Creek. Filter feeder insects are generally considered to be
more sensitive than other macroinvertebrates to dissolved metals in the water column.
Benthic macroinvertebrates that are generally absent downstream of the tailings piles
(excluding RC-3 at the mouth) are organisms that require a clean upper stone surface (ex.
"scrapers") and organisms that require open interstitial spaces for hiding. Bioassays
conducted by Ecology using Cladocerans (Ceriodaphnia), a sensitive filter feeder, and
Railroad Creek water collected from above and below the tailings piles, at RC-10, and at
RC-3 indicated no adverse effects.
.The benthic macroinvertebrate species composition, and the finding that.. fish and
macroinvertebrate populations were not reduced downstream of the major sources of
dissolved cadmium, copper and zinc loading to Railroad Creek, indicate that the reductions
in fish and macroinvertebrate populations adjacent to and downstream of the tailings piles
observed appears to be primarily attributable to the lack of suitable habitat or food sources
due to the presence of iron flocculent.
Human Health and Ecological Risk Assessment
The human health and ecological risk assessments analyzed, potential risks to human and ecological
receptors exposed to the compounds of potential concern within soil, surface water, groundwater,
sediments, and air at the Site.
The human health risk assessment found that the risks were acceptable for both residents
and visitors to the Site based on reasonable maximum exposure scenarios.
The ecological risk assessment found that:
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17693-005-019Uuly 28. 1999;12:16 PM;DRAFT FINAL RI REPORT ES- 10