Dames & Moore, 1999 - USDA Forest Service

MINTEQA2 indicates that the seep waters are saturated with respect to basic aluminum sulfate, alunite,
barite, and goethite. Copper concentrations are low in both cases, hence, copper concentrations do not
appear to be in equilibrium with any copper minerals. Analyses of ferricrete (formed by the precipitation
of iron oxyhydroxides such as goethite) have indicated copper concentrations up to 2,340 m@g. Copper
is expected to co-precipitate with goethite. The seeps tend to contain more zinc than copper but ferricrete
proportionately contains much less zinc than copper. Copper tends to attenuate as groundwater
containing ferrous iron is oxidized and goethite precipitates. Zinc attenuates to a lesser degree.
Tailings Piles 2 and 3
Mechanisms in the tailings pile 2 and 3 are identical to tailings pile 1. The seeps are geochemically
identical except that seeps SP-3, SP-4 and SP-5 are more dilute than SP-1 and SP-2. This is attributed to
partial mixing of Railroad Creek groundwater with seepage from the tailings pile and longer contact paths
with neutralizing materials. The fate of the seeps is the same as seeps SP- 1 and SP-2 from tailings pile 1.
6.6 RAILROAD CREEK
6.6.1 Surface Water Loading Analysis
6.6.1.1 Introduction
Dissolved metals enter Railroad Creek as seep flow, drainage flow and groundwater baseflow.
A chemical and flow mass balance analysis was performed for reaches of Railroad Creek that receive mine
drainage and reaches located upstream and downstream of mine influences. The purpose of the mass
balance was to:
(1)
(2)
(3)
(4)
assess metal contribution in drainage water from point sources measured during the RI in
relation to metal concentrations in Railroad ~ &ek upstream of mine influences
determine the point source discharges that contribute the highest metal concentrations to
Railroad Creek
assess if specific reaches within Railroad Creek contain non-point-source.or "unaccounted"
(assumed to be baseflow) metal load, and
evaluate the chemical loading analyses in relation to the water balance of select reaches of
Railroad Creek
Flow and metal co'ncentrations of seeps and drainages were measured during the FU to assess contribution of
these inputs to Railroad Creek during the May and September 1997 sampling rounds. Flow and water
quality measurements in Railroad Creek were repeated at selected stations in late ApriVMay 1998.
The effects of seep, drainage and groundwater inputs to the surface water quality of Railroad Creek are
observed by the changes in seasonal water quality conditions in a downstream direction. Dissolved metals
entering Railroad Creek in groundwater, seepage flow and flow from the 1500-level main portal drainage
and other drainages attenuate within Railroad Creek by dilution, acid buffering and adsorption reactions in
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17693-005-01 9Uuly 27.1999,4: 1 1 PM;DRAFT FINAL Rl REPORT