Dames & Moore, 1999 - USDA Forest Service

Ninemile Creek) with a corresponding increase in graveYsand and silt fraction. The change in substrate size
is related to channel slope and overall geomorphol~gic conditions (Section 4.3).
Assessment of sediment chemical characteristics as it relates to mining activities is difficult because of the
generally large grain sizes encountered. Therefore, previous sediment quality investigations have tended to
focus on the smaller grain size fraction. None of the investigations attempted to evaluate the depositional
environment or how representative the sediment samples that were collected are to typical conditions in
Railroad Creek. Sediment samples were not collected from Railroad Creek or tributaries to Railroad Creek
during the RI. Historical sediment data is described below.
Stream sediment samples were previously collected by USGS (1994), U.S. Bureau of Mines (1995), and
Ecology (1997). The historical data is summarized in Table 5.5-1. Historical samples did not include
ferricrete or flocculent media. The locations of historic sediment samples are shown on Figures 5.5-1 and
5.5-la. Metal concentrations in samples collected upstream of the Site (USGS, 1994) and tributaries to
Railroad Creek were all below Ecology's proposed Freshwater Sediment Quality Values (FSQV. 1997),
with the exception of copper at USGS station 346, which was 1,000 mgkg compared to the FSQV (340
mg/kg).
Sediment samples were collected at stations adjacent to and downstream of the Holden Mine. The data
were compared to upstream concentrations and FSQVs. Generally, .metals were below upstream
concentrations with the exception of cadmium, copper, iron, lead, and silver, which were above upstream
concentrations in a limited number of samples. Cadmium, copper, and silver were below FSQVs. An
FSQV is not established for iron. Iron was above upstream concentrations at only one location, station 350,
which is located east of Tailings Pile 3 in the area near location SP-18. .
Ecology (1997) compared metals concentrations in sediment samples collected from Railroad Creek to
assumed background levels for stream sediments in Washington, and sediment quality guidelines. The
comparison indicates that sediments in Railroad Creek upstream of the Site contained concentrations of
zinc, copper and lead at or below expected background levels, and were below concentrations for FSQVs.
Concentrations of'zinc and copper were reported to be above typical background conditions in sediment
samples collected in Railroad Creek adjacent to the Site; however, they were also below FSQVs.
5.5.2 Lake Chelan-Lucerne Bar and Stehekin
Sediment samples were collected in the fall of 1998 from Lake Chelan at Lucerne bar and at Stehekin
near the mouth of the Stehekin River in Lake Chelan. data collected from Stehekin were used to assess
reference concentrations. Data collected at Lucerne were compared to the reference concentrations and to
Ecology's FSQVs. The samples were analyzed for a limited list of metals (aluminum, arsenic, cadmium,
copper, iron, lead, manganese, and zinc) based on PCOCs identified in Railroad Creek. Additionally, the
samples were analyzed for total solids, total organic carbon, total volatile solids, and acid volatile solids.
The data are summarized with the statistical analysis in Tables 5.5-2 and 5.5-3. Sample locations are
shown on Figures 5.5-2 and 5.5-3.
The Stehekin reference concentrations were statistically analyzed to calculate a 90th percentile value
which is considered the reference concentration. The reference concentrations were compared to
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