Dames & Moore, 1999 - USDA Forest Service

West Waste Rock Pie, 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-11
(Figure 6.1-3a). As noted in Section 6i3.2, 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 femc oxyhydroxides, barite, copper carbonates and sulfates
(antlerite, brochantite, malachite - SP-15E, July 12, 1997), and cupricfemte. The copper minerals were
previously identified by the USGS (personal communication with Jim Kilburn, 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 p&) and zinc (267 and 2340 pga) concentrations and had higher pH (M.8) than the upslope
seeps. For SP-11, 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 fiom solution due to formation of
oxyhydroxide precipitates (oxidation and precipitation). This is implied by MMTEQA2
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 co-precipitation occurs.
Seasonal evaporation at SP-15E resulting in removal of copper from solution by
formation of copper sulfates (efflorescence); 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 resilting 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 mg/L). MINTEQA2 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
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1769M05019Uuly 27.1999;4:11 PM;DRAFF FINAL RI REPORT