Dames & Moore, 1999 - USDA Forest Service

decreases also, aiding in the dissolution of any sulfide material present. Metal salts found on the ground
surface and walls of the mill building are the result of the evaporation of metal-bearing water or its
interaction with native materials causing precipitation. Some of the metals become redissolved and
transported from the mill building.
The transport pathways associated with the maintenance yard are shown on Figure 6.5-4. Similar transport
pathways occur as compared to other Site features. Overland flow hm the area drains eventually into the
lagoon (Figure 6.1-3a). Infiltration associated with the maintenance yard area emerges as seep SP-22.
TPH was detected in the maintenance yard soil in a localized area up to two feet below ground surface
(bgs). The area is relatively flat and the primary transport mechanism is assumed to be infiltration from
surface run-on and snowmelt. The adsorption capacity of TPH in soil is assumed to be relatively high due
to the nature of the materials observed (clayey silt), therefore, TPH in soil most likely attenuates with depth
and lateral distance.
6.5.1.4 Downgradient Attenuation of Metals
This subsection qualitatively describes evidence of metal attenuation downgradient of the source areas. The
processes occurring at each location are also indicated by symbol coding (Figure 6.5-9).
Seeps SP-26, SP-23, SP-23B, SP-12 and 1500-Level Ventilator Portal Discharge
Seep SP-26 flows during the spring from the south bank of Railroad Creek downslope of the 1500-level
ventilator portal and a remnant detention pond feature. The analyses of the SP-26 sample detected
(Figure 6.1-3a) pH-neutral water with some alkalinity (10 to 14 mg/L). The chemistry of the water is not
comparable to mine discharge waters. Copper concentrations are 22 to 28 pgL compared to >lo00 p&
(in May) in mine discharge. These concentrations are too low to be controlled by the formation of a
copper carbonate. The copper concentrations possibly originate from the small detention pond that is
speculated to have collected water from the 1500 ventilator portal during backfilling of the underground
mine or from natural mineralization. The detention pond was observed to contain a small quantity, but
SP-26 water is very dilute and most likely represents meltwater.
Seeps SP-23, SP-23B and SP-12 flow during the spring from the south bank of Railroad Creek between
RC-1 and P-5 stations (Figure 6.1-3a). The results of laboratory analyses show many similar chemical
characteristics to waters originating from the mill buildings, mine and waste rock piles. Seeps SP-23 and
23B have pH