The construction and ventilation of sewers

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Ventilation of Sewers

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THE CONSTRUCTION AND VENTILATION OF SEWERS. ~ BY W. GRUGGEN,

L.R.C.P.I., D.P.H.,

President of the Home Counties Branch of the Incorporated Society of Medical Officers of Health; Medical Officer of Health of the Herts and Middlesex Comb. S.D.

THE construction and ventilation of sewers is a very important question to the medical officer of health, for, after all, he is the person who receives the blame if the sewage scheme is not a success, and has to face the abuse of the public after the engineer and contractor have left the work. A badly or even a carelessly constructed sewer does untold harm, especially from an educational point of view, for such sewer is sure to become highly offensive, thus leading the public to believe that all sewers must stink, that the water-carriage system is a failure, and that a return to the privy system is really best after all. The real purpose for which a sewer is constructed is to carry away filth from our dwellings as quickly as possible, and I contend that a sewer which does not keep the solid matter on the move from the time it leaves the dwelling till the time it reaches the outfall is a delusion. That this is the opinion of engineers whose opinion is worth listening to is obvious from the following quotations. Sir Joseph Bazalgette, when reporting on the London sewers in 1866, speaks thus with regard to ventilation : " T h e most universally applicable mode of preventing the escape of noxious gas is so to construct the sewers that a continuous flow shall be kept up in them,-and to provide them with a sufficiently copious supply of water that decomposing matters within them shall be diluted and instantaneously removed, and not allowed to settle and ferment in the sewers." Again, Mr. James Lemon, an engineer of considerable experience as President of the Section of Engineering and Architecture at the Sanitary Institute Congress at Portsmouth, in 1892, in his address to the Section, remarked that " i f we had properly designed and constructed sewers, we should hear very few complaints of the want of sewer ventilation." Now let us consider for a moment the requirements in construction of such a sewer. First, it should be laid in straight lines from manhole to manhole, and with a proper fall. Where a change of direction is required, a proper curve should be made of a sufficiently "~ Presidential Address, read October, 1898.

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long radius, entirely in the manhole, to allow the sewage to pass round the curve with the least possible retardation of the flow, and, in order to make up for the increased friction, the fall should be increased at this point. Branch sewers should join the main in manholes, each with a curve of sufficient radius. Another most important detail, but perhaps least often attended to, is that the sides of the channels in the manholes should be carried up vertically to at least the height of the top of the pipe ; for if this be not done, and the pipe be running full bore, the sewage will rise above the sides of the channel, cover the benching, and leave solid matter there to putrefy. Where the gradient is not all that can be desired, clean water syphon flushing tanks must be provided, that the sewer may be washed down at regular intervals, in case anything should happen to remain in it. The sewers must be made watertight, so that the water in which the solid matter floats may not leak away and leave the solid matter in the sewer. Where the sewer is below the ground-water level, it is necessary that it be watertight, to prevent ground water entering the sewer and causing trouble at the outfall ; but that does not help the particular point we are dealing with. I think I have enumerated the principal points that are necessary to ensure that the contents of the sewer reaches its destination in as short a time as possible. In speaking of sewer ventilation, I may again quote ~Ir. Lemon, in the address already referred to. He says: " I consider you cannot have too many inlets and outlets to a sewer, and after forty years' experience I have come to the conclusion that an open sewer down the centre of a street with a good fall, would be the best form of construction; this, however, is impracticable." Thus the more ventilation by manholes and shafts the better; but no amount of ventilation will make up for bad construction. There are other defects besides bad construction which may cause a sewer to be offensive, such as badly constructed house drains, overflows from cesspools, etc. ; but there is no possibility of a sewer being free from effluvia unless it is properly constructed. Now let us see what it is that we are occasionally given instead of this properly constructed sewer. It may be the lot of a medical officer of health to advise year after year that a town in his district should be provided with a proper system of sewers, in the belief that if he could only get his authority to carry out his suggestion all the nuisances which have given so much trouble in the past would be easily dealt with. A~ last the matter is seriously considered by the authority, an engineer is appointed, plans are

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got out, and a Local Government Board inquiry is held. The plans having been very carefully scrutinized by the Inspector, perhaps alterations suggested, and further plans prepared, it would appear to the uninitiated that there could not be any possibility of anything going wrong, or of the work being done in any but the best possible manner. Ultimately the work is commenced, and the medical officer of health thinks that his troubles are well nigh over as far as this place is concerned, and that the constant complaints of overflowing cesspools and foul ditches will come to an end. If he hears rumours of large quantities of water coming down to the outfall, and mentions the matter to the council or to the engineer, he is told he must wait until the work is finished before he begins to criticise. Then he " l i e s low," and tries to believe it will be all right. Branch drains are picked up as the work goes on, but no one seems to know what these connections are, what is the condition of the drains, nor what sort of stuff is coming down them--cesspool overflow, perhaps. At last the work is finished, but that excess of water is still coming down to the outfall, and looks beautifully clean at times. The tanks are perhaps all full, and the land which has been " l a i d o u t " (save the mark !) is a series of lakes, and no one seems exactly to know what to do. Then come complaints in the town of effluvia from the manholes, and not without reason, as the manholes are found to be mostly full of filth. When the filth is got out, it is found that the bottom of the manhole is shaped like a shallow V, with the point of the V level with th~ invert of the sewer. The free ends are probably sloped off in the wall of the manhole about level with the top of the sewer, a plan admirably calculated to prevent the solid matter ever getting to the ou¢fall, and to make the manhole a cesspool. The public are led to think that each manhole requires to be regularly cleaned out, and they begin to wonder why it should be thought better to have a row of cesspools in the street instead of one in the back garden. Then a further examination of the sewer is perhaps made, and it is found that a lamp in one lamphole cannot be seen at the next, although that length of sewer has been cleared out. The position of the medical officer of health at this stage is not a pleasant one. He has recommended sewers, and his recommendation has apparently been carried out. It is no use for him to say that by " sewers" he meant properly-constructed sewers. The public do not see the difference, and he is likely to come in for a fair amount of abuse. The remedy is simple, but costly, namely, to reconstruct the whole system. The water at the outfall tells of

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leaky sewers, the filth in the manholes of careless design and construction, and the whole must be done over again. Surely such a state of things should be impossible, but I dare say some of you will feel that they do occur oftener than they should. I cannot help feeling that the Local Government Board might take more interest in these schemes than they do. Once the plans are passed they take little more trouble, and every scheme is satisfactory, so far as they know, until application is made for a further loan for reconstruction. The return in the Board's Annual Report of schemes passed by them in the year might include the names of the engineer and contractor carrying out the scheme, and a report from the surveyor of the district as to its success. This may appear to entail a good deal of work, but it would surely be worth doing. The harm done to sanitation by bad work is untold. Much can be done by the authority, it is true, but not so much as seems on t h e surface. My own opinion is that the authority should always covenant for the new sewer to be handed over to them in an absolutely dry condition. No connections should be made until the sewer is in their hands, and no connections should be allowed to be made unless and until the drains to be connected are found to be thoroughly sound and properly laid. To be brief, properly-constructed sewers will not stink to such an extent that, if properly ventilated, any nuisance will be caused by the manholes. The proper course where stinks are complained of is to examine the sewer and not to close the manhole ventilation and put up a shaft (put up the shaft if you like, but do not close the ventilators). If the sewer be carefully examined the cause of the nuisance will be found; but it is much easier to put up a ventilating shaft than to examine the sewer, and probably find that you have to go ~o great expense to put it right. What I have said is not new, and I have not said it well, but it is a fact that authorities do not always get what they have a right to expect when they go to the expense of sewering a town. In conclusion, I feel that there are many points that I have omitted. We can all of us tell, no doubt, of falls the wrong way, of branch sewers joining the main in the walls of manholes 18 inches or so above the bottom, and covering the benching with filth, but I think I have said enough to provide something for discussion, and I feel that it is a matter which, like the sewer, requires ventilation. DISCUSSION. In the course of the discussionit was urged that insufficientflushing of housedrains was a frequent cause of nuisancein sewers, and so-c~led "hand flushing"

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of water-closets was emphatically condemned. The suggestion to deliver a new sewer " dry," i.e., with no connections to houses, was held to be impracticable, except in the case of a sewer laid where there was no pre-existing sewer. The practice of throwing sewerage schemes open to competition was objected to as imposing unnecessary restrictions on engineers, as was also the acceptance of tenders at prices which prohibited the use of the best materials and workmanship. The ventilation of sewers, in so far as the admission of fresh air was concerned, and in contradistinction to " vent" for foul air, was held by certain of the speakers to be unnecessary. Objectionwas taken to the occasional practice, now proposed for general adoption, of providing special sewer ventilators on the distal side of the intercepting traps of house-drains. It was urged that connections picked up in the course of constructing sewers should be examined as to course, condition, etc., and that careful plans and records should be kept of all sewers and branch drains.

PROCEEDINGS OF THE INCORPORATED SOCIETY OF MEDICAL OFFICERS OF HEALTH. FOUNDED, 1856. RECONSTITUTED, 1888. INCORPORATED, 1891. A MEETING Of the Society was held at No. 197, High Holborn, London, on Friday, November 11th, 1898. Present : Dr. E. Gwynn (President), in the Chair, Drs. W. T. G. Woodforde, R. Dudfield, W. Gruggen, J. Groves, L. T. F. Bryett, W. A. Bond, W. H. Symons, J. Wilkinson, Hugh Stott, W. Arnold Evans, G. F. Willoughby, A. Newsholme, Leonard Wilde, E. A. Dorrell, and F. J. Allan, Mr. Wolf Deifies, Members of the Incorporated Society, and Drs. Herbert J. Snow, Alex. S. R. Foulerton, and E. H. Roberts, Visitors. MINUTEs.--The minutes of the last ordinary meeting were read, and having been approved, were signed by the President. REPORT OF COUNCIL.--The Honorary Secretaries submitted the following Report of Council : November llth, 1898.--Your Council beg to report : 1. That they have appointed the President, the Editor, and the Hon. Secretary (Dr. Allan), to attend a Conference convened by the National Association for the Promotion of Technical and Secondary Education, to consider under what conditions a Plumbers' Registration Bill would be acceptable to the various bodies interested in the educa~ tion of plumbers. 2. That they have appointed a Committee to consider what further administrative or other measures can be taken to check the spread of tuberculosis, and have arranged that the meeting of the Society in January next shall be devoted to the consideration of the subject, when a discussion will be opened by Dr. Newsholme. 3. That a communication has been received from the Bournemouth Medical Society enclosing copy of a resolution passed by the Bournemouth Town Council making it compulsory on the Medical Officer of Health, when requested to do so by a medical man and before notification, to visit any doubtful case of infectious disease free of charge, and asking for the Society's opinion thereon. Y$ur Council recommend that a communication be addressed to the Bournemouth Medical Society (a) drawing their attention ,to the letter of the Local Govern-