Subsurface Laboratory Methods 273 



cium and magnesium are grouped as alkaline earths; sulphates, chlorides, 

 and nitrates are grouped as strong acids; and carbonates, bicarbonates, 

 and sulphides are grouped as weak acids. Thus, according to the reacting 

 value of these four groups, natural waters can be classified into four 

 types, i.e., primary saline, secondary saline, primary alkaline, and sec- 

 ondary alkaline. 



An excess of strong acids over weak acids causes salinity. It should 

 be noted that salinity can be due to either the sulphate or chloride radicle 

 or to both. The alkalies in connection with the strong acids cause primary 

 salinity, and an excess of strong acids with an equal value of alkaline 

 earths induces secondary salinity. 



An excess of alkalies over the strong acids with an equal value of 

 the weak acids makes up primary alkalinity, and an excess of weak acids 

 combined with aa equal value of alkaline earths produces secondary 

 alkalinity. 



Secondary salinity and primary alkalinity are incompatible; thus, 

 each natural water will have two or three of the above-mentioned proper- 

 ties but never all four. 



Primary salinity is common to all waters, and a primary saline water 

 is essentially a solution of sodium and potassium sulphates and chlorides. 

 A primary alkaline water consists principally of sodium and potassium 

 carbonates and bicarbonates. Calcium and magnesium sulphates and 

 chlorides predominate in a secondary saline water, and the water is per- 

 manently hard. Temporary hardness is present in a secondary alkaline 

 water consisting principally of calcium and magnesium bicarbonates. 



Surface Waters 



Surface waters in the Rocky Mountain region range from the dilute, 

 soft, alkaline waters of igneous terrain to moderately concentrated, hard, 

 rine beds. The usual mountain water derived from melting snow is soft, 

 alkaline, and dilute, but, after it has traversed marine sediments, calcium 

 and magnesium sulphates dominate the chemical system, and the water 

 often takes on a load of salts that makes it unfit to drink. 



The North Platte River, for example, rises in a network of mountain 

 streams in North Park, Colorado, and drains the southeastern quarter of 

 Wyoming. Near its source it is a primary alkaline type, but by the time 

 it reaches the Pathfinder reservoir it has been changed to a secondary sa- 

 line type. The Popo Agie, though dilute, is secondary saline near Lander, 

 Wyoming, whereas Castle Creek, Teapot Creek, and Salt Creek waters are 

 undrinkable because of the alkaline earth salts leached from the Steele 

 shale, as are the waters of many other smaller streams of Wyoming whose 

 drainage does not embrace the higher mountain areas. 



The influence of surface waters upon formation waters encountered 

 in drilling wells c^n be observed in a number of instances in Wyoming. 

 The most striking example is the Shannon sandstone along the western 



