DISPOSAL OF SEWAGE 509 



becomes reasonably clean and pure before its waters have pro- 

 ceeded far down stream. Sanitarians regard this as a primi- 

 tive and unscientific method of disposing of sewage. It is 

 generally believed that this method of disposing of city sewage 

 will, sometime in the future, be abandoned and more scientific 

 methods adopted. Most states in the east and central west 

 now control stream pollution, through Boards of Health, 

 proper disposal of sewage being required to suit conditions. 



600. Disposal of Sewage from Isolated Residences. In the 

 case of isolated buildings, such as farmhouses, country resi- 

 dences, and institutions out of reach of city sewer systems, 

 provision must be made for the final disposition of sewage. 

 In solving this problem, the laws and principles of science, as 

 far as they are understood, must be observed at every step. 

 Before this problem had been carefully studied many serious 

 mistakes were made. 



601. The Leaching Cesspool. Formerly the sewage from 

 an isolated residence was often conveyed into a cesspool (see 

 Fig. 294). Such a cesspool was merely a small, brick-walled, 

 well-like receptacle a few feet in depth dug in the ground. 

 No attempt was made to construct the cesspool water-tight. 

 It was intended that the liquid portions of the sewage should 

 soak, or LEACH, out into the surrounding soil. This, of course, 

 polluted the soil and, since the water table frequently rises to 

 a point near the surface of the soil, the ground-water became 

 contaminated. In fact, in cases where much water was sent 

 into the cesspool, the sewage constantly found its way down 

 into the ground-water, thus endangering all nearby wells (Fig. 

 315). If this same sewage had been spread thinly over the 

 surface of the soil, or better still had been covered by a few 

 inches of soil, it would quickly have been decomposed by bac- 

 teria and rendered harmless. Such bacteria are abundant 

 only near the surface of the soil; at the depth of the bottom of 

 a cesspool they are not numerous nor can they become numer- 

 ous, therefore, the sewage which leached from the old-style 

 cesspool into the ground-water was practically unaffected by 



