Dames & Moore, 1999 - USDA Forest Service

source areas was estimated from flow measurements and water quality results for seeps associated with
these areas collected in the spring and fall of 1997. The loading analysis included the data from seeps SP-
6 and SP-ISE, associated with the west waste rock pile, SP-7 and SP-22 associated with the mill area, and
SP-8 associated with the east waste rock pile. These seeps do not enter Railroad Creek as surface flow
and are considered to contribute to downslope seeps and ultimately to the alluvial aquifer. The loading
analysis was conducted to quantify the maximum load available from these areas that could contribute to
dissolved metals loading into Railroad Creek. The loading data are provided in Table 6.6-4 and shown on
Figure 6.5-20.
The data indicate that maximum loading from these source areas accounts for a small percentage of the
total load at RC-2 ranging from 0.2 to 2.9% for cadmium, 0.1 to 4.3% for copper, less than 0.01% for
iron, and 0.4 to 2.7% for zinc. The highest loads result from the mill area at SP-7 and the west waste
rock pile at SP-15E in the spring. The seeps used for the loading analysis were not flowing in the fall
except in response to significant precipitation.
A loading analysis was also performed for data collected from SP-21 located east of tailings pile 3 and
downstream of RC-2. Chemical data, direction of groundwater flow (especially in the fall), and the
documented loss of flow in Reach 2 (RC-4 to RC-2) indicate that affected groundwater from the tailings
and loss from Railroad Creek (unaccounted load) may be measurable at SP-21. Loading for dissolved
cadmium, copper, iron, and zinc were calculated using flow measurements and analytical data collected in
the spring and fall of 1997. The percentage load is based on RC-2 as an appropriate location downstream
of SP-2 1 on Railroad Creek was not established.
The analysis indicates that loading for these metals ranges from 0.8 to 1.2% in the spring and 0.1% or less
'. in the fall.
6.6.1.6 Conclusions
The following is concluded from the loading calculations:
All significant observed loads have been identified and accounted for in Railroad Creek.
Groundwater loads can be used to balance Site area chemical loading. Back-calculated
concentrations using flow estimates compare well with expected groundwater sources
such as mine discharge water and tailings seepage.
Copper and zinc loads to Railroad Creek from measured point sources and other
groundwater (baseflow) sources are highest during the spring snowmelt and groundwater
discharge period when groundwater levels are highest in the deep wells beneath the
tailings, and high flow occurs at the 1500-level portal drainage. During the May round
when flows are the highest, the portal drainage is the primary source of loading of
cadmium, copper and zinc to Railroad Creek.
Seeps SP-23 and SP-23B are the two next highest point sources that are estimated to
contribute cadmium, copper and zinc during May; however, this load drops to zero later in
the year as seep SP-23 dries up.
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17693-005419Vuly 27,1999;4:11 PM;DRAFT FINAL RI REPORT