Dames & Moore, 1999 - USDA Forest Service

Sources
The mining related waste contained within tailings piles 1, 2 and 3 is assumed to represent the source area
for potential human health exposure of metals of concern for the Site. The former mill building may also
act as a relatively minor metals source area In addition, a former storage area immediately north of the mill
was identified as a potential source of polychlorinated biphenyl (PCB) and petroleum hydrocarbons.
Potential Mieration Pathwaw
The mining related wastes and former storage area may contribute compounds of concern to air. surface
water, seeps, mine portal drainage, sediment, groundwater, and soil (surface and subsurface) at the Site. The
potential for site constituents to migrate from source media to points of exposure depends on their
distribution, physical and chemical properties of the constituents of concern, and properties of the media.
Transfer to these environmental media may occur via one or more of the following general mechanisms:
Leaching: Migration of Constituents from Soil or Mining Wastes to Groundwater,
Surface Water, and ~edimeni The infiltration of precipitation into the soil and tailings
and subsequent leaching into groundwater may result in the transfer of Site constituents
to the groundwater. This leaching process depends on several physical and chemical
characteristics of the constituents and the soil and tailings, including water solubility,
octanoVwater partition coefficient, oxidation/reduction potential, mineralogy, organic
carbon content, cation exchange capacity, and soiVtailings surface area. PCBs tend to be
tightly bound to the soil. The potential for metals to leach depends on the state of the
metal and soihilings characteristics. Once Site constituents reach groundwater, they
can migrate laterally and venically in groundwater throu& gross fluid movement and
dispersion. The rate of migration is dependent on aquifer characteristics and chemical
and physical characteristics of the constituent. Hydrophobic and cationic constituents
(e.g., PCBs) will migrate slower than water soluble and nonionic constituents (e.g..
metals). Additionally, Site constituents in groundwater can be transferred to surface
water through seeps or directly to a surface water body, and, in the case of the Holden
Mine, through mine portal drainage. Groundwater at the Site may discharge through
these mechanisms into Railroad and Copper Creeks. Once in surface water bodies, some
Site constituents have the potential of accumulating in sediment andfor fish.
Runoff: Migration of Constituents from Soil or Mining Wastes to Surface Water
and Sediment. Precipitation can carry Site-related constituents or suspended soil or
tailings into surface water bodies such as Railroad Creek and Copper Creek through
' storm water runoff processes. Erosion of the tailings pile also contributes Site
constituents to surface water. Once in surface water bodies, some Site constituents have
the potential of accumulating in sediment and/or fish.
Suspension: Migration of Constituents from Soils or Mining Wastes to Air. The
transfer of constituents present in soils or tailings to the air may occur through agitation
of the surface soils resulting in the generation of fugitive particulate emissions.
Volatilization is considered an insignificant migration pathway since the constituents
associated with the Site are nonvolatile metals and ,PCBs. Particulate emissions are
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176934054 19Uuly 27.1999,5:16 PWRAFT FINAL RI REPORT