396 IRRIGATION FARMING. 



with reference to the sewage reaching it by gravity. 

 If, however, the location does not admit of such pro- 

 cedure, pumps may be utilized, although this fre- 

 quently will entail considerable additional expense in 

 first cost of plant as well as in the annual outlay for 

 operation and maintenance. In some cases, where 

 land can be reached by gravity by going considerable 

 distance or can be covered by pumping within a short 

 distance, carefully prepared estimates, taking into 

 account all the elements of first cost, as well as the 

 annual cost of maintenance and operation, may show 

 that it is cheaper to deliver the sewage a long distance 

 by gravity than a shorter distance by pumping. 



Formerly it was also considered important to selec5l 

 a sewage farm with reference to the surrounding in- 

 habitation, because there was prejudice against such 

 farms on account of the assumed liability to effluvium, 

 nuisance. This objedlion has much less weight now 

 than it formerly had, because experience has fully de- 

 monstrated that with proper management a sewage 

 farm is no more objedlionable on account of bad smells 

 than any other form of farming. 



For best results the top-soil of a sewage farm should 

 be of permeable characfler, with a gravelly or sandy 

 subsoil. If it is compadl clay the sewage cannot enter, 

 and the only purification attained will be that due to 

 coming in contacft with the soil by flowing over it. It 

 is possible to so treat sewage and prepare a farm as to 

 attain a very high degree of purification even with 

 clay soils, but the chance of doing this at commercial 

 profit is exceedingly small. If not naturally level or 

 of very uniforni slope, a sewage farm for best results 



