Dames & Moore, 1999 - USDA Forest Service

Secondary mineralization and precipitates produced by weathering processes are visibly
evident at the Site, including orange brown iron stains (iron oxyhydroxides) on waste rock
and tailings, white precipitates (amorphous aluminum hydroxide) in the 1500-level main
portal drainage, green stain (copper carbonate) on marble waste rock in the waste rock
piles, and efflorescent crusts (metal sulfates) in .the mill building and where seepage
emerges along the toes of the tailings piles.
The differences in oxygen availability and water flow in the Site source areas influence the
geochemical characteristics of water quality at the Site. Portions of the underground mine
are well-oxygenated through the winter months' due to airflow induced by temperature
differences between the underground mine and the ambient air. Active oxidation occurs in
open stopes above the 1500-level of the mine. Random water flow occurs in fractures and
dissolves weathering products, some of which are discharged in the 1500-level main portal
drainage, and some of which are stored' as salts formed by evapo-concentration. The
tailings piles are only oxygenated near the surface; therefore, chemical processes leading to
the release of metals occur primarily in this zone and not at depth. .Acid neutralization
occurs at depth in the tailings piles. Groundwater beneath the tailings piles contains
reduced iron which rapidly oxidizes upon emergence in seeps, forming ferricrete and
f
flocculent.
The metal attenuation processes that occur downgradient of source areas prior to entering
Railroad Creek include precipitation due to pH increase and aeration, efflorescence
(causing seasonal formation of salts), co-precipitation of heavy metals (primarily with iron),
and adsorption. Precipitation of iron, aluminum, and copper flocculent probably occurs
when seeps mix with slightly alkaline a ail road Creek water and groundwater adjacent to
Railroad Creek.
Comparison of sulfate and aluminum supports the general conclus'ion of buffering by
alumino-silicates.
The chemical loading analyses completed during the RI accounted for the overland flow
and groundwater loading sources of dissolved metals to Railroad Creek.
Conclusions associated with the water quality and chemical loading of component inflow
sources including the portal drainage, groundwater, the waste rock piles, mill building,
Copper Creek diversion and seeps SP-12 and SP-23 are provided below.
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SUMMARY.dof
17693-005-01 9Uuly 28,1999; 12: 16 PM;DRAFT FINAL RI REPORT