willow Bypass and the Wildlife Ponds (Figure 3-4) . The Mill- 

 Willow Bypass is a manmade ditch along the edge of the Warm 

 Springs Ponds that contains the combined flows of Mill and 

 Willow creeks. The ditch was cut through historic tailings 

 deposits left by Silver Bow Creek before the ponds were built 

 and contains more recent tailings deposited when the creek is 

 allowed to bypass the treatment ponds during periods of high 

 runoff. 



An extensive bottom sediment sampling effort at the 

 Warm Springs Ponds was completed during the fall of 1987 as 

 part of the Phase II RI activities. The objective was to 

 gain an understanding of the volumes and chemistry of 

 sediments that have accumulated in the various settling and 

 treatment ponds. Average concentrations of selected metals 

 in bottom sediment samples collected for the Phase II RI are 

 provided in Table 3-8. 



The Warm Springs Ponds are designed to contain a flow of 

 about 700 cfs (U.S. Army Corps of Engineers 1978). Silver 

 Bow Creek flows greater than this are diverted around the 

 ponds into the Mill-Willow Bypass, where they continue 

 untreated into the Clark Fork. However, dike failure and 

 bypass due to collection of debris on the gates has occurred 

 at flows much less than 700 cfs (MultiTech 1987a) . Bypass 

 events occur on the average of once per year. Although no 

 water quality samples of Silver Bow Creek were obtained by 

 MultiTech during a bypass event, historic data and recent 

 studies by the Water Quality Bureau and DFWP (Phillips 1985) 

 show that such events trigger large increases in TSS and most 

 metals in the Clark Fork. 



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