Dames & Moore, 1999 - USDA Forest Service

I
. During
The water from the west waste rock pile (seeps SP-6, SP-15W. and SP-15E) flows overland to the lagoon.
the spring snowmelt period, the lagoon fills with the water and flows intermittently to Railroad
Creek; however, the above-mentioned seeps flowing into the lagoon accounted for approximately 4 percent.
6 percent, and 4 percent of the loading of cadmium, copper, and zinc, respectively, to Railroad Creek during
May 1997. Later in the summer the water levels in the lagoon drop and eventually completely dissipate.
The lagoon is coincident with the abandoned Railroad Creek stream bed. It is possible that the portion of
water. which does not evaporate infiltrates into the ground surface and flows as groundwater to Railroad
Creek, either as diffuse flow and/or through the abandoned streambed, which intercepts Railroad Creek near
seeps SP- I and SP-2.
During the spring snowmelt period, one relatively small seep (SP-8) flows from near the base of the east
waste rock pile and flows overland within a ditch across a portion of tailings pile 1 before entering the
Copper Creek diversion which flows directly into Railroad Creek. However, seep SP-8 accounts for
approximately 1 percent or less of cadmium, copper, and zinc loading to Railroad Creek.
Mill Building
Upslope surface water runon in the form of snowmelt and precipitation also infiltrates into upper
foundations of the abandoned mill building, which is not covered with a roof. Surface water passes through
the building and eventually flows overland into the lagoon. Unprocessed ore and residual salts in the mill
contribute metals to the water as it makes its way through the building remains and rubble. A seep (SP-7)
flows from the mill building before exiting a pipe that eventually drains into the lagoon. The seep flows
primarily during the spring snow melt period and accounts for less than 2 percent, 4 percent, and 2 percent
of the cadmium, copper and zinc loading, respectfully, to Railroad Creek. Seep SP-22 is located to the
north of the mill building and may represent metals loading from the mill structure; however, the seep
accounts for less than 1 percent of the cadmium, copper, and zinc loading to Railroad Creek.
Maintenance Yard
Surface water, in the form of runon and precipitation, infiltrate into the ground surface in the western
portion of the Site. Both surface water runoff and near-surface groundwater flow towards the lagoon. As
noted above, the water from the lagoon likely discharges both directly (surface flow) and indirectly
(subsurface flow) to Railroad Creek, as well as evaporates. Surface flow from the maintenance drains into
the pipe mentioned for the mill building above that eventually drains into the lagoon. Seep SP-22, which is
located to the north of both the mill building and maintenance yards, flows during the spring snowmelt
period only and accounts for less than 1 percent of cadmium, copper, and zinc loading to Railroad Creek.
8.4.4 Eastern Portion of Site
Groundwater originating upslope and upstream of the Site appears to flow underneath the relatively low
permeability tailings materials during the spring snowmelt period, resulting in an increase in hydrostatic
pressures and movement of some water up into the tailings piles. As the snowmelt dissipates, the pressures
decrease and the flow direction reverses. Low pH water and dissolved iron generated within the tailings are
released into the groundwater as it migrates through the tailings materials. The groundwater eventually
enters Railroad Creek either as seeps and/or diffise groundwater flow.
17693-005-019Uuly 28.1999;10:24 Ah4;DRAFT FMAL RI REPORT