Dames & Moore, 1999 - USDA Forest Service

and only started flowing afier several days of consistent precipitation. The general flow characteristics of
the seeps (i.e., presencelabsence, location, etc.) were observed during the 1998 RI field effort and found
to be similar to those observations made during the 1997 RI field effect.
The total average flow for seeps (SP-9, SP-I I: SP-12, SP-22, SP-24, SP-25, SP-6 and SP-7) that are
associated with'groundwater baseflow from the south side of Reach 1 for the MaylJune 1997 period was
estimated to be approximately 0.19 cfs, and for the September period was estimated to be approximately 0
cfs.
Based on the seep flow evaluation, SP-ISE and SP-15W flow measurements were included as
components of Qa. Seeps SP-23 and SP-23B were incorporated as a component of surface runoff, Qsr.
The total average seep flow for SP-9, SP-I I, SP-12, SP-22, SP-24, SP-25, SP-6 and SP-7 was not
included in the water balance because the flows represent groundwater and are already accounted for in
the groundwater component.
Reacb 2 Seeps
Referring to Figure 4.4-20, seeps that were observed during spring 1997 and 1998 to contribute to Reach
2 include SP-1, SP-2, SP-3, SP-4, SP-8, SP-IOE, SP-IOW and SP-19. Seeps SP-5, SP-17 and SP-18 flow
to the east of RC-2 and, therefore, do not flow into Reach 2 of Railroad Creek. Instead these seeps
contribute to flow observed at seep SP-21, which includes seep flow and runoff from the slopes south of
tailings piles 2 and 3, as well as runoff from tailings piles 2 and 3 (Figures 4.4-20a through d).
Seeps SP-I, SP-2, SP-3,'SP-4, SP-IOE, and SP-IOW are all considered surface expressions of flow from
the alluvial aquifer which underlies the tailings piles. Seep SP-5 and SP-18 are also considered to be
expressions of flow from the alluvial aquifer beneath the tailings piles; however, they flow easterly
beyond RC-2 (as mentioned above). Seep SP-17 primarily reflects runoff routed into the cutoff ditches
upgradient of the tailings, routing this flow to SP-21. SP-8 and SP-19 are associated with intermittent
flow from the base of the east waste rock pile upslope from tailings pile 1 and include snowmelt runoff
from surrounding areas and, to a limited degree, from the surface of tailings pile 1. Table 4.4-8
summarizes the range of flow observed in the above seeps, and an assumed average flow for the
MayIJune and September 1997 periods.
As noted for the seeps observed in Reach 1 of Railroad Creek, the majority of seeps in Reach 2 were
observed to flow only during the spring sampling event (MayIJune 1997). Referring to Figure 4.4-21,
several exceptions were seeps SP-1 through SP-3, which were observed to flow during both the spring
and fall sampling events. In addition, seep SP-21 was observed flowing during the fall sampling event
after several consecutive days of precipitation. Seep SP-8 was observed flowing from the base of the east
waste rock pile in late May 1997 only.
The average total seep flow associated with groundwater baseflow from the tailings piles was estimated to
be approximately 0.18 cfs (excluding SP-5 and SP-21) for the MayIJune period, and 0 cfs for September.
Flow in seep SP-21 includes both surface runoff from the upgradient slopes during MayIJune and
groundwater baseflow originating downstream of Tailings Pile 3. During the September 1997 period,
flow in seep SP-21 appears to reflect groundwater baseflow only.
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17693405-019Uuly 19. 1999:4:51 PM;DRAFT FINAL RI REPORT