Dames & Moore, 1999 - USDA Forest Service

At approximately 3 miles downstream of the Site (sampling station RC-10). 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
fiom 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 obsdrved .
appears to be primarily attributable to the lack of suitable habitat or food sources due to the
presence of iron flocculent.
9.2.7 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:
9.2.7.1 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.
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17693-005-019Uuly 28. 1999;10:07 AM;DRAFT FINAL RI REPORT