142 



DOMESTIC WATER SUPPLIES FOR THE FARM 



remedy is a tight packing between the two pipes at a point near 



the surface. 



Wells encountering open passages are practically limited to 



limestone in which solution channels have been formed by cir- 

 culating waters and later abandoned. In 

 Figure 64, which shows such a well, B is 

 the pump tube and C an open passage 

 into which air entering at the mouth of 

 the well during periods of high pressure 

 is carried off into the rock, producing 

 a circulation which soon freezes water 

 standing in the inner pipe. The treat- 

 ment is the same as that required for the 

 well just described; it consists of plugging 

 the space at E. 



In many wells, however, this treat- 

 ment is ineffectual, indicating that the 

 cold air is not entering at E, but is cir- 

 culating through underground passages, 

 as indicated by the arrow at D. In such 

 wells it becomes necessary to set the plug 

 at the point where the passage is en- 

 countered, in this case at D. In some 

 wells, as in one near Wabasha, Minn., 



the crevices through which the air is circulating are so numerous 



that the space between the outer and inner tubes must be filled 



from bottom to top with cement. 



FIG. 64. Conditions govern- 

 ing freezing in limestone wells. 



