Dames & Moore, 1999 - USDA Forest Service

5.3.8 Lake Chelan
5.3.8.1 Historical Data
Surface water data were not collected from Lake Chelan during the R1; however, in 1989, Patrnont reported
the results of an assessment of water quality conducted in Lake Chelan for Ecology in 1986. The report
noted that the "observed in-lake concentrations of total recoverable arsenic, iron, and zinc exhibited
temporal or spatial variations over the study period, and averaged 0.22 + 0.01 p a, 3.6 + 1.4 p a, and 2.0 +
0.1 pg/L, respectively. The only discemable variation in metals was observed in the iron data, as in-lake
levels peaked (6-12 pg/L)in lake surface waters during the spring, probably as a result of runoff inputs."
Also noted in the report was that concentrations detected were below the applicable aquatic life, water
quality criteria and drinking water standards (EPA, 1986). .
5.3.9 Surface Water Quality Summary
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Data collected from upstream stations in Railroad Creek were compiled with data collected fiom tributaries
to Railroad Creek (Holden Creek, Big Creek, Copper Creek, and en mile Creek) and reference streams in
the Stehekin area (South Fork Agnes Creek and Company Creek) to assess area background surface water
quality. Background values were statistically derived under the MTCA guidance and compared to both
Washington State and federal WQC where available. Where WQC were hardness corrected, a conservative
value of 6.7 ppm was used for the state criteria as well as a minimum hardness value of 25 ppm for the
federal criteria. The statistically derived background values are below state and federal WQC with the
exception of lead (0.54 pa) and silver (C 0.04 pa) which are above state CWQC and AWQC,
respectively. Lead and silver are below the federal WQC.
Site data collected fiom Railroad Creek adjacent to and downstream of the mine-affected area were
compared to WQC where established and background concentrations and MTCA Method B cleanup levels
if WQC were not available. PCOCs were identified if concentrations were above WQC or MTCA Method
B cleanup levels. Metal concentrations that were above background concentrations were identified as
compounds of interest to assess with PCOCs in the fate and transport and risk assessment discussions in
Sections 6.0 and 7.0.
Copper, cadmium, iron, and zinc were identified as PCOCs in surface water in Railroad Creek at the stations
adjacent to and downstream of the Site dependent upon sample location and sampling event. A summary
table listing the sample station and sampling event with the PCOCs identified in Railroad Creek is located in
Section 5.3.3.5. Aluminum and manganese concentrations were above background at stations adjacent to
and downstream of the Site dependent upon sample location and sampling event. Parameters such as pH,
dissolved oxygen, and specific conductance were generally similar at stations upstream, adjacent to, and
downstream of the site. The highest concentrations of metals in 1997 correlated with the highest flow in
Railroad Creek measured in May 1997. Concentrations for most metals increased downstream O~'RC-1 at
RC-4. Concentrations from RC-4 (downstream of the portal drainage) to RC-2 (downstream of tailings pile .
3) were similar or slightly decreased with the exception of iron which increased significantly at RC-7
(adjacent to tailings pile 2). Concentrations generally decrease from RC-2 to RC-3 at Luceme. At several
stations adjacent to and downstream of the mine area, metal concentrations measured in 1998 were above
1997 concentrations. The difference in concentrations is likely relateh to the time and position of the
sampling event on the hydrograph (Section 4;O).
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17693-005-019Uuly 28. 1999;11:09 AM:DRAFT FINAL RI REPORT