- 70 - 



High concentrations of sodium and bicarbonate also occur in the Fort 

 Union (Ravenscrag) Formation but chloride concentrations are substan- 

 tially lower than those in the Fox Hills-Hell Creek aquifer. Most of the 

 Hart coal wells in the Fort Union Formation have higher concentrations of 

 calcium and magnesium than sodium, but water quality in a localized group 

 of wells (13 and 15) resembles that of other Fort Union beds suggesting 

 hydraulic continuity between the coal and non-coal aquifers. 



Water quality of the shallow unconsolidated deposits resembles that of 

 the Fort Union, suggesting a common flow system for these units. 



Sampling for water quality was performed annually on wells listed in the 

 quantity section until 1989, when the schedule was reduced to wells 5-11 

 13, 15, and 19. 



There has been little variability over time in the toal dissolved solids 

 at selected wells as indicated in Figure 60. 



Figure 60. — Total dissolved solids concentrations for water from 

 selected wells during the period of sampling. 



