coulees and "seeped" drainageways were included, the affected area 

 would be much greater. Saline seep is known to be highly destructive 

 to Montana's soil, water, and wildlife resources, but the true extent 

 of its adverse environmental effects is only guesswork. 



Although aggravated by the crop-fallow system now in use, 

 the saline seep problem stems from the geology of the northern Great 

 Plains region. The surface material is glacial till up to 70 feet 

 thick. The till is underlain by a thick marine shale formation that 

 is impermeable to water. Both the till and the shale contain an 

 abundant supply of natural soluble salts. Excess water, evidently 

 produced by dryland moisture conservation, moves through the till, 

 picks up salts, and builds up on top of the shale, froming a "perched" 

 water table. This excess water gradually moves downslope, accumu- 

 lates in the lower swales, and eventually reaches the surface and 

 evaporates, leaving the dissolved salts behind (Figure 1). 



This paper outlines the history of the development of saline 

 seep in Montana and efforts to control it; it describes in detail the 

 hydrogeological setting of the area affected and notes the potential 

 for spreading throughout much of the northern Great Plains. The 

 latter portion of the paper deals with environmental aspects and 

 implications of saline seep, including environmental impact and possible 

 control technologies. 



