of metals for the basin, samples were collected from isolated 

 outcrops of the Missoula Lake Beds, which contain only 

 natural concentrations of metals (Moore 1985) . 



The mainstem Clark Fork sites were five to six river 

 miles apart between the Warm Springs Ponds and the Milltown 

 Reservoir. Where possible, fine-grained sediment from the 

 upper layers of bank deposits on the lowest terrace near the 

 main channel was sampled. Such samples would represent the 

 most recent sediment deposited outside the channel. Between 

 the ponds and Garrison, the sediments were in many places 

 actually tailings, with green and blue copper sulfate and 

 carbonate precipitates on exposed surfaces. The tailings 

 were thickest near the Warm Springs Ponds (over three feet) 

 and decreased downstream (Moore 1985) . 



Results of this study indicate several trends in the 

 distribution of metals in the floodplain sediments. Arsenic, 

 copper, and lead concentrations showed a distinct decrease 

 downstream from the upper reaches to about Flint Creek, a 

 slight decrease until Rock Creek, and then a slight increase 

 near the Milltown Reservoir (Figures 3-9, 3-10, and 3-11). 

 Cadmium and zinc showed similar trends, although concentra- 

 tions were more erratic with strong spikes along the 

 mainstem. The mainstem sediment metal levels were generally 

 orders of magnitude higher than tributary and Missoula Lake 

 Bed levels, suggesting that Clark Fork floodplain sediments 

 are extremely enriched over natural background concentra- 

 tions. However, distribution of the contaminated sediment is 

 not uniform, as two of the mainstem sample sites (river miles 

 7 and 17) contained only background levels of metals (Moore 

 1985) . Such an occurrence would not be that unusual in an 

 active fluvial system. The area between Racetrack and Flint 

 Creek, with a fairly wide floodplain, appears to be a major 

 depositional environment, whereas the narrow floodplain 

 downstream of Flint Creek to above Milltown Reservoir likely 

 restricts such deposition (Moore 1985) . 



Hydrometrics (1983b) conducted an inventory of tailings- 

 affected areas between the Warm Springs Ponds and Deer 

 Lodge. Fifteen samples were collected from five sites, 

 including both well-vegetated sites and those that appeared 

 to have been affected by tailings. Results of chemical 

 analyses showed considerable variability in the tailings, but 

 generally showed high concentrations of aluminum, copper, and 

 zinc. From field examination and aerial photo interpreta- 

 tion, Hydrometrics estimated that one million cubic yards of 

 tailings covering about 1,250 acres have been deposited on 

 the floodplain between Warm Springs and Deer Lodge. A 

 reconnaissance study of tailings deposits between Deer Lodge 

 and Garrison indicated that tailings are present as scattered 



3-46 



