Dames & Moore, 1999 - USDA Forest Service

Creek diversion, and Copper Creek. The data is compared to WQC where available and appropriate.
Where WQC were not available, the data were compared to statistically calculated area background and
MTCA Method B cleanup levels for surface water. Calcium, magnesium, sodium, and potassium
concentrations were not individually evaluated as these metals are considered nutrient metals. Water
hardness was considered in the discussions as WQC for several metals is based on hardness.
The discussions incorporate historical data (where appropriate) and RI data. The surface water quality
discussion primarily focuses on the RI data collected; however, historical water quality and stream flow data
is available for Stations RC-1, RC-2, and RC-3 and at other locations sampled by USFS, PNL, USGS and
Ecology. Due to the varied analyte list per historical sampling event and variable detection limits, the
comparability and usability of historical data is discussed in appropriate sections. The data are assumed to
be of adequate quality to include in the RI, for comparative purposes unless otherwise noted. Historical data
for Railroad Creek, Copper Creek, Copper Creek diversion, and the portal drainage are available and
summarized in tables referenced in the appropriate sections. These data were collected over several studies
and were previously evaluated by Dames & Moore (1996). Additional data collected by the USGS and
Ecology in 1996 have been evaluated as well.
The intent of the discussion is to identify data trends and PCOCs that will be further evaluated in the
compounds of concern fate and transport discussion and the human health and ecological risk assessments.
PCOCs were identified if concentrations were above WQC or above statistically calculated area background
concentrations or MTCA Method B cleanup levels where WQC are not available. Statistics were used in
the human health and ecological risk assessments and the calculations incorporate both RI and select
historical data as appropriate. ,
5.3.1 Background Surface Water Quality in Railroad Creek
5.3.1.1 Background Data Sets and Statistical Methods
Metals data collected from the 1997 and 1998 RI data sets and historically from stations upstream of the
Site were compiled to assess area background surface water quality in Railroad Creek. RI and select
historical background surface water data from the following stations were used in the area background
assessment:
Railroad Creek (RC- 1 1, RC- 1, RC-6)
Holden Creek (HC-1, HC-2, HC-3, HC-4, Holden Creek)
Big Creek (Big-1)
Copper Creek (CC- 1, upstream of the Site) .
Ten Mile Creek
Reference reaches in the Stehekin watershed from South Fork Agnes Creek (SF Agnes
Creek) and Company Creek (Both of these creeks originate from the same headwaters as
Railroad Creek)
Historical data collected from Railroad Creek by the USGS from 1994 through 1996
(USGS 367, USGS 546, USGS 600, USGS 707)
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