As a result of changes instituted during the smelter 

 demolition, the Opportunity Ponds system is in a state of 

 physical and geochemical flux. Tailings areas that were 

 continuously flooded since the early 1950s as a dust control 

 measure are now draining. At present, the only external 

 source of water to the site is treated wastewater from the 

 city of Anaconda. This source may be discontinued in the 

 near future. As the tailings dry out, an oxidizing front is 

 predicted to move down through the tailings. Acid produced 

 during this process could liberate significant quantities of 

 trace metals to the ground water system. 



Elimination of surface water to the site has resulted in 

 increased wind migration of contaminants to adjacent areas, a 

 gradual lowering of the ground water elevation across the 

 site, and the potential for increased contamination movement 

 into ground waters as tailings become oxidized. Assuming 

 that the remedial investigation is validated, additional 

 investigation activity is likely to focus mainly on providing 

 information for the evaluation of permanent control strate- 

 gies. Possible control options for the ponds include a 

 variety of capping alternatives, erosion control measures, 

 ground water containment, and perhaps ground water treatment. 

 AMC has already invested millions of dollars towards 

 controlling fugitive emissions by covering the ponds with 

 limestone as they dry out. Ground water conditions in the 

 vicinity of the Opportunity Ponds are discussed in more 

 detail later in this chapter. 



Warm Springs Ponds 



The Anaconda Copper Company constructed three treatment 

 ponds near Warm Springs, Montana,. in 1911, 1916, and between 

 1954 and 1959. The purpose of the ponds was to settle out 

 industrial wastes to improve the quality of water released to 

 the Clark Fork. Lime has been added to pond inputs on a 

 seasonal or streamflow basis since 1959 to aid in precipi- 

 tating dissolved metals. 



The ponds cover about 2,800 acres, and Hydrometrics 

 (1983a) estimated that they contain approximately 19 million 

 cubic yards of mill tailings, mine waste rock, natural 

 sediments, and precipitates. 



A comprehensive study of the ponds is now underway as 

 part of the Silver Bow Creek Superfund site investigations. 

 Phase I of this study was conducted by MultiTech (1987b) and 

 Phase II is being conducted by CH2M Hill. For this Superfund 

 investigation, the study area extends from the upper pH shack 

 on Silver Bow Creek to below Pond 1 and includes the Mill- 



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