30 



The total calculated seepage from the ash lagoons in 1999 was determined to be 1 .70 litres per second. 

 There has been little change in the individual seepage rate, or the vertical and horizontal components 

 that make up the total seepage rates, from 1 992. This was expected because there has been little 

 change in the operating levels of the lagoons over the last several years. 



3.3.3.2 Montana 



Samples were collected from monitoring wells 7, 1 6, and 24 during 1 999. Well 7 is completed in Hart 

 Coal, well 16 is completed in the Fort Union Formation, and well 24 is completed in alluvium. No 

 significant changes in TDS were observed in monitoring well 16. The TDS in the Hart Coal (well 7) 

 and the alluvial aquifer (well 24), however, increased about 100 mg/L during the years 1996 through 

 1998, but decreased about 50-70 mg/L during 1999. Graphs of total dissolved solids for selected 

 wells are shown in Figure 3.18. 



Figure 3.18 Total Dissolved Solids in Samples from Montana Wells. 



