Dames & Moore, 1999 - USDA Forest Service

The water quality data collected from South Fork Agnes Creek and Company Creek were included in the
area surface water quality background assessment discussed previously in Section 5.3.1. Both of these
creeks originate from the same general headwaters as Railroad Creek. The arsenic concentration (2.56
pgL) in South Fork Agnes Creek was an order of magnitude above the concentration detected in Company
Creek (0.13 pg/L). The arsenic concentration may be the result of historical prospecting and mining
activities in the Stehekin River area and was not included in the background surface water quality
assessment. The arsenic concentration is well below CWQC (190 pg/L) and AWQC (360 pg1L).
The data collected from Bridge Creek was compared to WQC or background and MTCA Method B cleanup
levels if WQC were not available. Metal concentrations were below WQC. The remaining metals were
below background and MTCA Method B cleanup levels with the exception of molybdenum.
Molybdenum (1.02 mg/L) was above background (0.78 pg/L). The elevated molybdenum concentration
may be related to mining activities in the Stehekin area.
The field sample data for Bridge Creek were compared to additional parameters specified in WAC 173-
201A. Where data were available, criteria were not exceeded with the exception of pH. The measured
pH at Bridge Creek was 6.4 SU just below the criterion of 6.5 to 8.5 SU.
5.3.3 Railroad Creek
Samples were collected from Railroad Creek upstream of the Site (RC-1, RC-6, and RC- I I), adjacent to
the tailings piles (RC-4, RC-7, and RC-2), and downstream of the Site (RC-5, RC-5A, RC-10, RC-8, and
RC-3) to assess the influence of the Holden Mine on the water quality of Railroad Creek.
5.3.3.1 Historical Data
Historical data were compiled for RC-I, RC-2, and RC-3 from studies conducted from 1982 to 1983 (USFS
1983) and 1989 to 1995 (PNL, 1989 to 1992; USFS, 1993 to 1995). In addition, the USGS collected
samples near RC-I, and in proximity of the RC-2 and RC-3 stations in 1994, 1995, and 1996, and Ecology
collected samples in 1996 at RC-I, RC-2, and RC-3. The data are summarized in Tables 5.3-19 through
5.3-21. Sample locations are shown on Figures 5.3-1 and 5.3-4.
The list of metals analyzed varied with sampling event and sampling agency. The bulk of the metals data is
total recoverable with the exception of the USGS and Ecology data which included dissolved data.
Hardness values were available for some data points, but not all, and the omission precluded calculation of
hardness corrected criteria. Detection limits for most of the data are higher than assumed WQC and higher
than detection limits achieved during the RI. Due to the number of results reported as not detected, trends
were difficult to assess and direct comparison to the RI data or assumed WQC was not feasible. In addition,
the historical data collected by the USGS, USFS, and PNL in the Railroad Creek reach adjacent to the Site
indicated high variability of chemical concentrations. Each agency collected samples from a different
portion of the creek span.
The USGS samples were collected from near the south bank of Railroad Creek, USFSJPNL samples were
collected from the north bank, and Ecology samples were collected midstream. Samples were collected as
grab samples. Samples collected during the RI specifically to address whether differences of chemical
concentrations occurred within the creek channel indicated that samples from the south bank in the reach
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