Dames & Moore, 1999 - USDA Forest Service

sulfate discharged from the portal greatly exceeds the mass of copper, zinc, iron and cadmium discharged at
any given time.
6.5.1.2 Waste Rock Piles
Air Movement
Like mine workings, differences in temperature are important considerations in determining weathering
processes (Figure 6.5-6). In summer, the interior of the pile is anticipated to be cooler than the ambient
temperature and there is no process to drive oxygen deep into ihe pile. Oxygen enters the pile from the
surface driven by diffusion leading to oxidation in the immediate pile surface only.
The decrease in temperatures in the winter potentially creates optimal conditions for convective air flow
(Figure 6.5.-6). Warmer temperatures in the pile &e created by heat generated by the oxidation processes.
The temperature difference allows air to be drawn into the base of the pile providing further oxygen for
oxidation. The process is self-perpetuating and indicates that winter can result in significant increases in
internal temperatures. This also allows oxidation rates to accelerate and encourages weathering products
to accumulate.
In the spring, melting of snow results in flushing of accumulated salts by cold water (Figure 6.5-6). This
can cool internal temperatures, and coupled with rising ambient temperatures, serves to reduce oxidation
rates.
Water Flow
; The locations of the waste rock piles are shown on Figure 6.1-la. Four waste rock piles are discussed and
include the west and east waste rock piles, and the 800- and 1100-level portal waste rock piles. Waste rock
,
. piles associated with the 300, 500 and 700 portals are located on bedrock and are relatively small. There
was no field evidence of seep discharge or surface water overland flow observed at these piles; therefore,
they are not firther discussed.
In the spring, upslope snowrnelt run-on flows as overland flow and infiltrates on the slopes south of the
waste rock piles and within each rock pile. Weathering products accumulated during the winter are leached.
In general, groundwater moves downslope in the alluviaYreworked till unit and in the soiVfill material,, and
, discharges either as seep overland flow or as goundwater baseflow into Railroad Creek (Figure 6.5-4).
The spring conceptual groundwater flow path is to the north and northeast from the waste rock piles toward
the intermittent drainage for the 800- and 1100-level waste rock piles, and toward Railroad Creek for the
east and west waste rock piles, as shown on Figure 6.5-7. Some portion of groundwater flow is presumably
diverted into the abandoned Railroad Creek channel. Groundwater in the alluvium/till that flows from the
west waste rock pile appears to emerge as intermittent seeps, SP-6 and SP-I SE, and continues as overland
flow to the lagoon (Figures 6.1-3a).
Groundwater from the east waste rock pile appears to emerge as an intermittent seep (SP-8). Surface water
. flow from SP-8 flows overland across tailings pile 1 and is expressed as seep SP-19 before flowing into the
Copper Creek di,version (Figure 6.1-3a).
\\DM-SEAl\VOLI\COMMOMWP\~~\holdm-2Li\60.6oc 6-29
17693-M)5019Uuly 27.1999;4:11 -RAFT RNAL RI REPORT