Dames & Moore, 1999 - USDA Forest Service

A loss of flow was identified behveen P-1 and P-5 in July and September 1997 (Figure 4.3-7). It is
assumed that a loss also occurred in MayIJune 1997, but was not measurable due to high flow conditions.
The observed flow loss ranges from 0.1 1 cfs in July 1997 to 0.06 cfs in September 1997. Assuming that
the loss in flow is related to the log-discharge in the drainage, an estimate of flow loss from the drainage
between P-1 and P-5 was calculated to be in the range of 0.35 cfs for MayIJune, and 0.06 cfs for
September. Loss from the portal contributes to the shallow alluvial aquifer (Qa) and is reflected.,in the
estimate for this inflow component (see Section 4.4.4.8).
Seep Flow
Seeps seasonally emerge along the streambanks, at the base of the tailings and at the base of the waste
rock piles. In determining the overall estimate of inflow from the alluvial aquifer (Qa), seep source flows
were evaluated for use in the water balance as described below.
Reach 1 Seeps
Referring to Figures 4.4-20 and 4.4-21, seeps that were observed during spring to contribute to Reach 1
. include SP-6, SP-7, SP-9, SP- 1 1, SP- 12, SP-1 5E, SP- I SW, SP- 16, SP-22, SP-23, SP-23B, SP-24, and SP-
25. The likely flowpaths of water (overland and underground) at the Site to Railroad Creek are illustrated
on Figures 4.4-20a through d and indicate inflow to Railroad Creek starting from upstream of the Holden
Mine to downstream of tailings pile 3.
Seeps SP-6 and SP-7 flow from the west waste rock pile and mine workings located in the vicinity of the
1 500-level main portal. Both of these seeps contribute flow to SP- 15E and SP- 15 W and, as part of SP- 15,
flow eventually into the lagoon (SP-16). The lagoon has a limited surface outlet and, therefore, inflow
generally infiltrates over the course of the year, contributing to recharge of the alluvial aquifer which
underlies the lagoon. Thus, the flow from the lagoon appears to contribute to subsurface outflow from the
alluvial aquifer to Railroad Creek.
Seeps SP-9, SP-1 I, SP-12, SP-24 and' SP-25 emerge during spring along the south bank of Railroad
Creek, and are considered expressions of surface outflow from the alluvial aquifer. Seep SP-22 does not
flow directly into the creek, but instead appears to infiltrate into the alluvial aquifer, contributing to
aquifer recharge and, therefore, subsurface flow into Railroad Creek.
Seep SP-23 appears to form an independent flow system that emerges adjacent to Railroad Creek,
downslope of an avalanche chute which originates in the Honeymoon Heights area, and the intermittent
drainage which flows adjacent to the 800- and 1100-level waste rock piles; however, the source of the
seep SP-23 water has not been determined. Seep SP-23B appears to be an extension of SP-23 that flows
subsurface along the streambank. Flow from seeps SP-23 and SP-23B was estimated to be 0.17 cfs for
the MayIJune 1997 period, and 0.05 cfs for September 1997, reflecting a response to a somewhat different
recharge condition as compared to the groundwater seeps. Table 4.4-7 summarizes general flow data for
these seeps for the MayIJune and September 1997 periods, based on Table 4.4-8a.
As noted on Table 4.4-7, the majority of seeps observed within Reach 1 during the spring sampling event
(MayIJune 1997) were not flowing during the fall sampling event (September 1997). It should also be
noted that during the fall sampling event, seeps SP-7 and SP-23 had not been flowing since early summer,
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17693605-019Uuly 19.1999;4:51 PM:DRAFT FNAL RI REPORT