Dames & Moore, 1999 - USDA Forest Service

Infiltration of water from the portal drainage to the underlying alluvial aquifer may
account for metals concentrations in seeps located downgradient from the portal drainage
that flow into Railroad Creek or to groundwater baseflow.
Iron enters RaiLroad Creek primarily by groundwater and iron loads are greater in
September than May. Iron loads enter Railroad Creek downstream of the load sources
(i.e., portal drainage) for cadmium, zinc and copper, which enter the creek as surface
flows or seeps.
Similar results were obtained in spring 1997 and 1998. Differences in absolute loadings
were observed and can be attributed to differences in timing of monitoring. The 1998
monitoring was conducted during the initial part of snowmelt, likely resulting in the
measurement of greater loads of copper, zinc and cadmium entering Railroad Cmk.
Additional source areas located at the west and east waste rock piles and the mill area are
not significant loading sources to Railroad Creek. Metals loading at SP-2 1 may account for
a component of unaccounted loads noted in September.
6.7 COMPARISON OF THE HOLDEN MINE WITH OTHER MINE SITES
This section provides case example comparisons of two other mines with characteristics similar to the
Holden Mine. The examples are relatively typical of hard rock metal mines in northwestern North
America and were selected on the basis of similar mine configuration, comparable waste types and
leaching of similar elements. These cases illustrate that the chemical processes operating at the Holden
Mine Site have been documented elsewhere, are not unique to the Holden Mine, and demonstrate that the
Site does not represent extreme mine drainage conditions.
6.7.1 Baker Mine
-The Baker Mine is a small underground gold mine located in a sub-alpine area in north central British
Columbia. Similar to the Holden Mine Site, the Baker Mine experiences winter conditions during which
a snow pack forms. In June, the snow pack melts releasing large quantities of water in a few weeks.
Summers are relatively warm and dry with occasional thunderstorms. The fall is wetter before snow
starts to accumulate in October. The summer is shorter than at the Holden Mine Site, but the overall
climatic conditions are comparable.
Although the Baker Mine is much smaller than the Holden Mine, the configuration of the workings is
comparable (Figure 6.7-1). Mine drainage exits from a single portal. A second portal is located 100 feet
above this portal, and a small open pit is located on the slopes immediately above the mine; mine
drainage does not flow from these L o workings. The mine exploited an epithermal gold vein for a few
years in the early 1980s and is now being reclaimed. The immediate mine sequence contains little
carbonate. Two bulkheads were installed in the portals in 1993 with the intention of flooding the mine.
However, as a result of leakage around the bulkheads, holes were drilled in the bulkheads to allow water
to drain freely.
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17693405-019Uuly 27.1999,4:11 PM;DRAFT FD4AL RI REPORT