Dames & Moore, 1999 - USDA Forest Service

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West Waste Rock Plle, Mill Building, and Seeps SP-9 and SP-11
This pathway includes seepage from the west waste rock pile and runoff from the abandoned mill
building that collects in the lagoon (SP-16) before entering Railroad Creek at seeps SP-9 and SP-I 1
(Figure 6.1-3a). As noted in Section 6.3.2, the chemistry of these waters are all similar indicating weakly
acidic conditions with pH control by precipitation of aluminum hydroxides and sulfates. Chemistry is
also controlled locally by the formation of ferric oxyhydroxides, barite, copper carbonates and sulfates
(antlerite, brochantite, malachite - SP-1 SE, July 12, 1997), and cupricferrite. The copper minerals were
previously identified by the USGS (personal communication with Jim Kilbum, 1999) (Table 6.1-1) and
during the RI. The weakly acidic seeps at SP-9 and SP-11 contain lower sulfate (44 and 82 mg/L), copper
(3 and 460 pg&) and zinc (267 and 2340 pg/L) concentrations and had higher pH (>5.8) than the upslope
seeps. For SP-I I, the difference appears to be a dilution effect possibly by mixing with weakly alkaline
runoff water. The increase in pH probably resulted in copper precipitation but did not affect zinc. SP-9 is
further diluted in zinc and copper concentrations.
It appears that this pathway involves both permanent and seasonal removal of metals from solution.
These include:
Permanent removal of iron and aluminum from solution due to formation of
oxyhydroxide precipitates (oxidation and precipitation). This is implied by MINTEQA2
calculations and confirmed by field observations.
Probable co-precipitation of other metals with iron and aluminum (copper). Analysis of
precipitates elsewhere on the Site have. confirmed that ceprecipitation occurs.
evaporation at SP-1SE resulting in removal of copper from solution by
formation of copper sulfates (emorescence); these salts were observed. Spring seepage
... -.' waters are undersaturated with respect to these minerals, therefore, they will redissolve.
. .
Mixing of alkaline waters with weakly acidic waters resulting in the formation of basic
copper carbonates (malachite). The shift in pH dictates that this will occur.
Contact of weakly acidic waters with carbonate-containing rocks, resulting in the
formation of basic copper carbonates (malachite). Green coatings have been observed on
marble blocks exposed on the surface of the west waste rock pile.
Seeps SP-22 to SP-25 and SP-24
Seep SP-22 flows from the slope below the maintenance yard, mill building, and west waste rock pile
(Figure 6.1-3a). The chemistry of the seep resembles other seeps in the vicinity,. although when
monitored in May 1997, it had a pH of 6 and weak alkalinity (7 m a). MNIEQA2 indicates that the
water is in equilibrium with amorphous aluminum hydroxide. This implies that this water has been
influenced by the same processes occurring in the waste rock piles, but that it has been significantly
diluted rather than mixed with alkaline water or contacted alkaline materials.
Seeps SP-24 and 25 flow from the south bank of Railroad Creek north of seep SP-22. The seeps are
chemically very similar to SP-22 except that the pH is lower. Aluminum concentrations are higher due to
the lower pH. Overall, the chemistry of seeps SP-22, SP-24 and SP-25 are comparable to other seeps in