284 Ground Water, Wells and Farm Drainage. 



place the pump so as to draw the water from the bottom 

 where it is coolest and freshest. 



Both depth of soil, to act as a filter, and time to bring 

 about changes in surface waters, to free them from organic 

 matter, are required in order to render the water falling 

 upon the ground pure and suitable to drink. 



352. Temperature of Well Water. The zone of lowest 

 ground temperature is generally from 20 to 70 feet below 

 the surface and in this zone the coldest waters are pro- 

 cured. Above 20 feet the waters will be colder in winter 

 and warmer in summer and below 70 to 75 feet the water 

 generally becomes warmer from the internal heat of the 

 earth. 



The normal temperature of the coldest well water in a 

 locality is usually from 2 to 4 degrees higher than the mean 

 annual air temperature of the place, and in Wisconsin this 

 ranges from 43 in the northern portion to about 50 in 

 the southern portion. 



353. Well Casing or Curbing. Everything considered 

 there is probably nothing better for a curbing or casing for 

 a well than the 6 inch lap-weld steam pipe. The same pipe 

 galvanized is better because it will not rust out so quickly. 

 The great advantage of this kind of casing is that it is so 

 completely water tight and at the top can be so securely 

 closed as to prevent insects and vermin falling in. 



Next to the steel casing is one made of cement tile or 

 glazed sewer tile with their joints set in cement. "Where a 

 well is to have a brick or stone curbing the upper 10 feet 

 should be laid in cement and plastered with the same on the 

 back to exclude surface water and vermin. 



354. Top of the Well In finishing a well the casing 

 should be carried 12 to 18 inches above the surrounding 

 surface and then earth be .graded up to it so as to secure per- 

 fect and quick removal of all surface water. 



