sample site was approximately 9 km downstream from the foot of the glacier. 

 Other high suspended solids and turbidity values were recorded at the 

 Dietrich and Middle Fork Koyukuk River sites. 



Turbidity measurements recorded at the Middle Fork Koyukuk River- 

 Downstream site exceeded water quality criteria for water supply. The only 

 other beneficial use standard exceeded was the aquatic life standard for 

 turbidity at Phelan Creek. This parameter was exceeded by approximately 340 

 percent during August. Phelan Creek water should still be considered con- 

 sumable, depending on other (unmeasured) parameters. Most values exceeding 

 the Alaska Water Quality Standards reflected a natural situation with only 

 suspended solids at Dietrich River-Downstream possibly induced by gravel 

 remova I . 



The pH and ORP values measured at all sites reflected a basic condition 

 that was neither oxidizing nor reducing. The ORP values were relatively high 

 because of the high dissolved oxygen concentrations. The pH and ORP values 

 showed that there were very little organics in the monitored waters and that 

 most of the heavy metals would be insoluble. Some of the pH values were 

 slightly high (i.e., at Tanana R i ver-Upstream, pH = 8.5-9.0 in the two pits) 

 and may be associated with some heavy metal solubilities. 



Water Quality Changes at Gravel Removal Sites. Most of the water 

 quality changes observed as the receiving waters passed through the aban - 

 doned gravel removal sites can be associated with physical changes in the 

 stream . A major change was reduced water velocity within the mined area 

 promoting sedimentation, warming of the water, and stratification. At other 

 sites physical changes affecting water quality conditions include a steep- 

 ening of the bottom gradient through the mined site, which would increase 

 the velocity of the water and increase the scour of the bottom sediments. 



Turbidity and suspended solids changes were observed between the up- 

 stream and mined, mined and downstream, and upstream and downstream study 

 areas at 19 of the sites (Table 37). The changes are expressed as the per- 

 centage change occurring from the upstream samples to the downstream 



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