DRIVEN AND JET WELLS 



99 



Ordinarily, especially when the depth of the water-bearing 

 stratum is unknown, a screen (Fig. 43) is inserted between the 

 drive point and pipe, and the well is tested from time to time by a 

 suction pump screwed to the top of the pipe (in case of shallow 



FIG. 43. Types of screen and well points. 



wells) or by deep well pumps inserted within the outer tube (in 

 case of the deeper and larger wells). 



\Yhen a satisfactory supply is reached the well is generally 

 subjected to heavy pumping for several hours to draw from the 

 strainer and the surrounding materials the finer materials, clay, 

 etc., leaving a natural filter surrounding the screen as shown in 

 Fig. 44. 



