GENERAL CONSIDERATIONS 9 



that therefore it would be economy to combine the two and 

 build one sewer for the two purposes. In what streets this 

 should be done, and how far it is economy to do it, must be 

 determined by careful study and comparative computations. It 

 is as grave a fault to design a separate sewer for a street that 

 needs a storm-water sewer discharging into the same outfall as 

 to build a storm-water sewer where none is needed. 



It is often possible, in reconstruction or improvements, to 

 use an old sewer for storm-water alone with entire success, 

 building new sewers for the house-sewage. It is therefore 

 necessary to know with accuracy the sizes and grades of all old 

 sewers in order that if possible they may be incorporated into 

 the design in hand. 



The regulations of the different State Boards of Health are 

 in many cases the real cause of determining whether a separate 

 system or a combined system shall be built. In New York 

 State, for example, no system of sewers in any community may 

 be built unless, according to the laws, the places have received 

 the approval of the State Department of Health. This approval 

 is withheld as a matter of established policy for plans showing 

 combined sewers discharging without the action of a disposal 

 plant into inland waters. Since the cost of purifying or 

 even treating storm-water is financially as impossible as it is 

 unreasonable, it follows that in New York State all sewer 

 systems are now built on the separate plan and the necessary 

 storm drains are built according to a separate design. 



Where combined sewers are already in operation and it is 

 proposed to make extensions for the sake of house connections, 

 the attitude of the Department of Health is made to agree with 

 local conditions. If the extension is long compared with that 

 part of the combined system affected, they may require new 

 separate sewers laid to replace the old pipes. If short, they 

 may require the entire sewer system to be replaced by pipes for 

 domestic sewage, the system discharging into a disposal plant. 

 The construction of this last, or at least its design and a promise 

 to construct, is often made a condition precedent to grant- 



