20 



BULLETIN 190, U. S. DEPARTMENT OF AGEICULTUEE. 



Ordinarily, a satisfactory relief well may be bored with an 8-incli 

 post-hole auger. It should be cased with tile or pipe, or filled with 



Grounc/ Surface, 



Drain 6 feet deep 

 at change ofs/ope^ 





Fig. 13. — Section showing relief-well method applied to the drainage of lands receiving water from a deep 



pervious stratum. 



coarse gravel. ReUef wells in gravel, however, develop so much 

 water that it is necessary to excavate a pit and build in a lumber or 

 concrete box. 



EiG. 14.— Section showing method of draining soils underlain by hardpan at a shallow depth by the use of 

 relief weUs. Intercepting drain cuts off seepage carried on the top of the hardpan. 



DRAINAGE OF SOIL HAVING HARDPAN SUBSTRATUM. 



Another case in which rehef wells may contribute toward efficiency 

 is shown in figure 14. In this case, which is frequently met with, a 

 stratum of hardpan is found at a shallow depth, this being underlain 



