534 PROCEEDINGS OF SECTION H. 



lies not in closing the ventilato^^s or erecting tall flues — these may 

 mitigate the evil — but in such improvements to the sewers and 

 house drains as will hasten the removal of the sewage before de- 

 composition has set in. The system of ventilation may be 

 defective, insufiicient openings being provided. 



The advisability of separating the rain water from the sewage 

 can no longer be questioned. The Royal Commission on Metro- 

 politan Sewage Discharge (London) have approved of this course. 

 In several instances where sewage works have been designed and 

 executed in accordance with this principle they have proved 

 eminently satisfactory. The common or combined system has 

 always proved unsatisfactory and always will do so. This system 

 arose in a very natural manner in the old cities where numerous 

 drains and sewers existed for the purpose of removing surface 

 water. These sewers formed very convenient receptacles for house 

 slops and refuse of all kinds which it was thought would be 

 effectively removed by the recurring rains. But Avhile awaiting 

 this removal the refuse matter decomposed and proved very 

 hurtful. No wonder rain was looked upon as a welcome and 

 necessary scavenger for the sewers, and a strong feeling prevails 

 to this very day that it is absolutely necessary to admit rain 

 water to all sewers for the purpose of cleansing them. There is 

 a system known as the partially separate system in which elaborate 

 precautions are taken to admit only a certain percentage of rain- 

 fall to the sewers. This system appears to be based upon the 

 popular idea that rain water must be admitted to sewers in order 

 to keep them clean. Sewerage systems can now be designed, 

 having sewers which will keep clean without the aid of rain water, 

 and such are very desirable in climates where rain falls at long 

 and uncertain intervals. It will never do to depend upon the 

 rain to keep the sewers clean in this climate. All sewage should 

 go to the sewers, and rainfall to the natural channels. The ex- 

 clusion of sewage from the rain water channels permits of a 

 different method of construction, and instead of the separate 

 system proving a greater expense than the combined, it may be 

 constructed more cheaply and bring untold benefits in its train. 

 The exclusion of rain water from the sewers enables them to be 

 proportioned in size to the quantities of sewage to be removed. 

 The quantity of sewage to be removed from a known population 

 on a given area can readily be ascertained when the amount of 

 the water supply is known. This amount can always be ascertained, 

 and the velocity being fixed at three feet per second, the size of 

 the sewer, and the grade are both readily determined. 



In many instances the natural conformation of the surface will 

 render the desired grade unattainable in the ordinary manner, 

 especially if the area be flat. This grade must be obtained — 

 sanitary science is unyielding in its demands — therefore, under 

 such conditions the hydro-pneumatic, or hydraulic ejector system, 

 must be resorted to. 



