Dames & Moore, 1999 - USDA Forest Service

covered with flocculent. The flocculent was observed in suspension during higher stream flows created by
snow melt andlor storm events.
The Railroad Creek substrate was also observed to contain ferricrete that is cemented in isolated places.
Observations both during the RI and by others document the ferricrete to be limited to portions of the south
bank of Railroad Creek near the northwest and northeast comers of tailings pile 1 and the northwest comer
of tailings pile 2, generally coincident with the locations of seeps SP-1,2, and 3, which are further described
below.
Downstream of Site
Downstream of the Site, it appears that Railroad Creek is in a net gaining condition throughout the year.
Measured streamflows between the Site and the mouth of Railroad Creek generally increases on the order of
two to three times. Portions of Railroad Creek between mile 5-112 (measured from the mouth) to
approximately one-half mile upstream of Luceme flow directly atop bedrock. Several waterfalls, estimated
to be on the order to 50 or more feet in height, exist throughout this segment of Railroad Creek.
The last approximately one-half mile of Railroad Creek near the mouth flows atop alluvial sand and gravel.
It is likely that this portion of the creek may be losing a relatively small amount water to these alluvial
materials in which the USFS Luceme guard station water supply well is installed.
The iron-oxide staining andlor flocculent ,were observed on the creek substrate to slightly east and
downstream of the Sevenmile Creek confluence at RC- 10. Suspended iron-oxide flocculent was observed
in Railroad Creek throughout the stream reach from the Site to the mouth during spring melt and storm
events.
Results of Hydrologic Modeling
Streambank Erosion
The results of the hydrologic modeling indicated that the existing riprap height would be marginal in
protecting the tailings pile slopes during a 100-year storm event. The area with the highest potential for
overtopping by Railroad Creek was the northwest comer of tailings pile 2 immediately downstream of the
Copper Creek confluence.
Riprap Size
The results of the modeling indicated that some of the riprap is not of adequate size to prevent removal
during a 100-year event. As noted earlier in this section, the existing riprap appears to be actively eroding;
therefore, the size of the riprap will decrease over time. Areas with some riprap of marginal size included
the majority of tailings pile 1, the eastern half of tailings pile 2, and the majority of tailings pile 3. The size
of riprap immediately downstream of the confluence of Railroad Creek and Copper Creek generally
appeared adequate. The removal of inadequately sized riprap during a storm event may result in delivery of
tailings materials to Railroad Creek.
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17693-005-019Uuly 28. 1999;10:24 AM;DRAFT FINAL RI REPORT