Ponds discharges and can be considered a source of contamina- 

 tion to the Clark Fork. The metals-removal efficiencies of 

 the pond system during the Phase I RI study period exhibited 

 seasonal variation. In the summer months, the ponds showed 

 high metals-removal efficiencies, presumably due to low input 

 rates and higher pH. During the period of June 1 to 

 September 15, 1985, the removal efficiencies for total copper 

 and total zinc were 97 percent and 96 percent, respectively. 

 The drop in pH that occurred during the winter months and 

 possibly other factors, such as channeling, may have allowed 

 more dissolved cadmium, copper, and zinc to pass through the 

 ponds without being precipitated, resulting in lower metals- 

 removal efficiencies. 



Because the initial remedial investigation was under- 

 taken during a period of drought and low streamflows, the 

 influence of typically high spring runoff inflows to the pond 

 system was not thoroughly evaluated. However, higher flows 

 during the spring lowered the pond's efficiency due to higher 

 contaminant loads and reduced residence times. Solid phases 

 of copper, iron, and zinc, as well as arsenic and lead, were 

 released in large quantities during this period. It appears 

 that the hydrologic regime and algae populations (which 

 influence pH and bioaccumulation of metals) are the most 

 important mechanisms governing the contaminant load the ponds 

 deliver to the Clark Fork (MultiTech 1987a) . 



Phase II RI surface water investigations at the Warm 

 Springs Ponds focused on the collection of surface water 

 samples at key locations within the area at regular intervals 

 throughout a 2 4 -hour period. - These diurnal samplings were 

 conducted in September 1987 and in January, April, and July 

 1988. The objective of the samplings was to determine the 

 efficiency of the pond system in removing metals from Silver 

 Bow Creek through a 24-hour period on a seasonal basis. 

 Field parameters measured included pH, EC, DO, and tempera- 

 ture. Three forms of the metal contaminants (total, acid- 

 extractable, and dissolved) were analyzed to determine the 

 bioavailability of metals travelling through the system and 

 to better define the behavior of metals constituents over a 

 24-hour time interval. A data report on the diurnal 

 samplings is expected to be released in early 1989. 



Water Quality Bureau monitoring data show that the Warm 

 Springs treatment ponds are extremely effective at decreasing 

 metals loads, concentrations, and toxicity in Silver Bow 

 Creek. On the average, treatment provided by the ponds 

 decreased annual Silver Bow Creek copper loads nearly 12- 

 fold and zinc loads about 5.5-fold during the 1985-87 period. 

 Metals concentrations in the 'creek, after passing through the 

 pond system, were an order of magnitude less. From 1985 to 

 87, copper toxicity criteria were exceeded slightly more than 



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