DEEP DRAINAGE SYSTEM I\ ADELAIDE. 553 



second doubtful. By these alterations the engineer has declared 

 that the ventilation in the sewers has been improved, while the 

 inhabitants are no longer assailed in their comfort or their health. 



I will now pass briefly in review the whole position and indicate 

 the direction in which something still remains at fault. It is to 

 be clearly remembered that complete dilution of sewer air by 

 atmospheric air is the only safe condition for any system 

 of sewerage. And no portion of the system should remain un- 

 touched by a circulating atmosphere. If this is not done, stagna- 

 tion and foulness will arise. The Adelaide system presents the 

 the following features : — They are small in dimensions and have 

 a good fall. Their contents are rapidly removed and permit no 

 time for the formation of sewer gas. They are thus capable of 

 easy veritilation. If by closing seven-eighths of the grids and 

 adding a few six-inch ventilating shafts the ventilation is greatly 

 improved, my last assertion is proved. 



An important fact, which is not compatible with a perfect 

 system of ventilation, must not be lost sight of, viz., that at least 

 nine-tenths of the house-connecting drains lying between the 

 street sewer and " boundary trap " are iinventilated cul-de-sacs. 

 Considering the large number of such connections, it is pei'fectly 

 evident that a large portion of the system remains at present 

 un ventilated. In the house-drains on the house side of the 

 " boundary trap " there is through venlUafAon, and no com- 

 plaint has ever once been made of this part of the system, while 

 it is equally notable that all trouble has arisen on the sewer side 

 of the "boundary trap" where no through ventilation exists. 

 Note also whatever improvement the engineer declares has been 

 made, is by the further introduction of this through ventilation. 



To attain through and therefore complete ventilation in the 

 whole deep drainage system, two causes are possible — open in. 

 every case the sewer side of the " boundary trap " and attach a 

 ventilating shaft to it — or abandon the " boundary trap " itself. 

 In suggesting this latter course, I do not forget Professor Corfield's 

 warning "that the traditional faith in the trap has been great, 

 and it is not orthodox even to suggest a doubt of its usefulness." 

 If we will only note clearly the fact that small sewers, rapid 

 removal of contents, and even a moderate amount of through 

 ventilation, will not permit the formation of sewer gas, it is plain 

 that by the insertion of an obstacle which the " boundary trap " 

 undoubtedly is, we create that very condition which we wish to 

 avoid. That is we get an accumulation of foul air, the "boundary 

 trap " having become the creator of the necessity for its own 

 existence. Every house possess a series of ventilating shafts, some 

 more, some less. The sum of the matter therefore is this, by the 

 removal of the " boundary trap " each of these shafts would be 

 brought fully into play, and ample means of ventilating the ivhole 

 system would be found. In summer, when the ventilation is 



