In addition to the continuous monitors, a flow-activated 

 automatic sampler was installed in August at the Stewart 

 Street Bridge. This sampler is triggered when increasing 

 streamflow reaches a predetermined level and then collects 

 water samples at predetermined time intervals. This sampler 

 was to be rotated around the four sites, but because of low 

 streamflows and lack of storms, it was kept at the Stewart 

 Street Bridge through September. It was then moved to the 

 Colorado Tailings location and operated through October. 

 Samples were collected during six storm events (both rain and 

 snow) at these sites. 



The automatic sampler was removed at the end of October 

 1988 and the continuous monitors were removed in the first 

 week of November 1988. Data are being analyzed by MBMG and 

 should be available by February or March 1989. 



Current Surface Water Quality 



Current surface water quality conditions in Silver Bow 

 Creek, the Warm Springs Ponds, and the mainstem Clark Fork 

 are discussed in the following sections. The discussion of 

 metals, sediment, and nutrients draws primarily from Silver 

 Bow Creek RI , DHES-WQB, and USG3 data. Much of the WQB data 

 is presented in the form of box plots. These plots graphi- 

 cally display the maximum, median, minimum, 25th percentile, 

 and 75th percentile values as shown below. In cases where 

 some of these percentile values are the same within a data 

 set for a given station, percentile lines overlie each other. 

 If all the values are the same, the plot is simply a 

 horizontal line at that value, indicating either a small data 

 set or no variation in measured values. 



■Maximum 



-75th Percentile 



-50th Percentile (Median) 



-25th Percentile 



-Minimum 



In this discussion, water quality parameters are 

 referred to both in terms of constituent concentration and 

 constituent load. Concentration is the weight of a given 

 constituent per unit volume of water, e.g., milligrams of 

 phosphorus per liter. Load is the weight of a given 



3-64 



