172 commission on building districts 



Statement by Amos Schaeffer, Consulting Engineer, Borough of 



Manhattan, May 15, 1916 

 Sewer systems 



All sewer systems for carrying off domestic sewage and surface drain- 

 age from cities are generally divided into two classes, namely, combined and 

 separate. In the combined system, sewers are built to take both the storm 

 water drainage and the domestic sewage, which is usually discharged into 

 some adjacent stream or harbor. In the separate system there are two 

 independent systems of sewers, one of which carries off the storm water 

 and the other the domestic sewage. The latter system is generally installed 

 when it is intended to purify the domestic sewage before it is finally dis- 

 charged. 



Inland cities and towns which discharge their sewage into fresh water 

 streams usually are required to treat their sewage to a high degree of 

 purity before discharging it, because the same stream is frequently used 

 as a source of water supply by some other municipalities. 



Operation and final disposition 



The combined system of sewers practically requires no attention for its 

 operation with the exception of seeing that the sewers are cleared of obstruc- 

 tions and are kept in proper repair. 



The sewage from the separate system of sewers is usually purified to a 

 sufficient degree of refinement so as not to pollute the waters into which the 

 effluent is discharged. These purification plants generally consist of grit 

 chambers, screens, sedimentation tanks and filters. One or all of these 

 processes are used according to the degree of purity required in the final 

 effluent. 



Development of the sanitary system 



Before the introduction of a water supply into cities, the domestic 

 sewage is usually allowed to flow into cesspools. When a municipality has 

 increased sufficiently to require a general water supply, the sanitary condi- 

 tions also require improvement and cesspools are usually superseded by 

 sewers built in the public highways, which serve all the property fronting 

 on them. In the case of seaboard cities, these sewers usually discharge 

 into the adjacent harbors without any purification. 

 Condition of sewers in New York City 



Sewers were constructed in this city as early as 1840 or thereabouts. 

 At that time cement was not available and the mortar used in their construc- 

 tion consisted usually of oyster-shell lime and sand. Due to the chemical 

 action of the sewage, the mortar has deteriorated to such an extent that a 

 great many of the sewers have practically none left in the joints, as a con- 

 sequence of which they are collapsing. At the time these early sewers were 

 constructed the science of sewer design had not advanced to the degree of 

 accuracy of to-day. 



The conditions under which these sewers were designed were also dif- 

 ferent from the present. The pervious area was very much larger than it is 

 to-dav, in consequence of which a considerably smaller quantity of rain 

 water reached the sewers and a much larger quantity was absorbed by the 

 soil. The roadwavs of the streets were usually paved with a waterbound 

 macadam or with some other material which was much more pervious than 

 the present pavements, and sometimes they were not paved at all; and the 

 sidewalks were frequently paved for a width of only four feet. The build- 



