The effects of the Stone wastewater discharge on 

 nutrient concentrations in the Clark Fork are less striking 

 than the Missoula WWTP discharge, in part due to the 

 additional dilution water provided by the Bitterroot River. 

 Phosphorus and nitrogen concentrations (see Figure 3-28 for 

 phosphorus) were marginally higher from above to below the 

 Stone Container discharge (bracketed by stations 20 and 22) , 

 and the frequency of exceedence of the phosphorous criterion 

 increased only slightly in FY 85-87. The nitrogen criterion 

 was never exceeded in samples from above or below the plant 

 in FY 85-87. Stone Container's current wastewater discharge 

 permit specifies that it shall attempt to reduce nutrient 

 concentrations and loading in its effluent to pre-1983 

 levels to meet nondegradation standards. If Stone Container 

 is unable to meet those reductions by the end of 1991, a 

 formal review will be conducted and the Montana Board of 

 Health will make a final determination of appropriate loading 

 limits for the facility. Limits will be designed to protect 

 current and anticipated beneficial uses. 



One way to accomplish this goal is to minimize nutrient 

 additions in the wastewater treatment process, and the FY 85- 

 87 data indicate that this approach is in fact reducing 

 nutrient concentrations. Mean total phosphorus and total 

 inorganic nitrogen concentrations were reduced by nearly half 

 from FY 85 to FY 87. Reductions in nutrient loading are more 

 difficult to assess because of the low streamflows during the 

 monitoring period and because the mill's allowable wastewater 

 discharge rates depend on streamflow. However, the FY 1987- 

 estimated phosphorus and nitrogen loads from the facility 

 were a third and a quarter, respectively, of the loads 

 discharged in FY 85. The FY 87 phosphorus and nitrogen 

 contributions to the Clark Fork from Stone Container are 

 estimated to be about ten tons per year each. Clearly, the 

 facility has made progress in its efforts to reduce nutrient 

 discharges. 



From the Stone Container mill to the Flathead River 

 confluence, nitrogen and phosphorous concentrations decline 

 as numerous small-to-medium-sized tributaries provide 

 additional dilution water and as biological uptake occurs. 

 Nitrogen and phosphorus loads remain roughly constant or 

 decline slightly, indicating a lack of significant nutrient 

 sources in this reach of river. The phosphorus criterion was 

 exceeded in 13 to 36 percent of the samples for the FY 85-87 

 period from below Stone to the Flathead River. Exceedences 

 were less frequent with increasing distance downstream of 

 the two point source discharges in the middle river. 



3-90 



