Anaconda and Opportunity Ponds 



Tailings from operations at the Anaconda Smelter were 

 slurried into a series of ponds northeast of the smelter 

 complex (Figure 3-3) . The first pond. Opportunity A, was 

 built in 1914. The Opportunity B, C, and D ponds were 

 constructed as needed through the next 40 years. Anaconda 

 pond 1 was constructed in 1943, and Anaconda pond 2 was built 

 in 1954. Together, the Anaconda and Opportunity ponds cover 

 approximately 4,000 acres and contain an estimated 185 

 million cubic yards of tailings material (Tetra Tech 1987) . 



Wastes in the Anaconda and Opportunity ponds are 

 relatively homogeneous compared with other wastes in the 

 upper Clark Fork because they are almost all mill tailings 

 generated at the smelter. However, even the materials in 

 this system exhibit considerable physical and chemical 

 variability due to evolving smelting processes, extensive 

 reworking of the deposits, and variabilities in the parent 

 ores. Average concentrations of several key trace elements 

 are 210 ppm arsenic, 470 ppm lead, 2,030 ppm copper and 1,200 

 ppm zinc (Tetra Tech 1986b) . 



An initial remedial investigation (Tetra Tech 1986b, 

 1987) has been concluded for the Anaconda and Opportunity 

 ponds. Included in the remedial investigation were waste 

 characterization, surface and ground water studies, ground 

 water modeling, and geochemical modeling. Waste charac- 

 terization studies indicated the following: 



• In most of the tailings boreholes, three zones were 

 recognized: an oxidizing zone in the upper part of 

 the tailings, a transition zone, and an unaltered 

 reduced zone. 



• Concentrations of arsenic and most metals were 

 generally lower near the tailings surface, in- 

 creased with depth, and then decreased. 



• The tailings are underlain by carbonate-rich 

 alluvial gravels. At the tailings-alluvium 

 interface, dramatic decreases in metal concentra- 

 tions usually occurred, although the levels in the 

 upper alluvium were still elevated relative to 

 typical background values. Where multiple samples 

 were recovered in the alluvium, the deepest samples 

 often approached background levels. 



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