CHAPTER II. WATER CARRIAGE SYSTEMS. A theoretically perfect sewer would be one in which all of the sewage would be carried rapidly to its outfall outside of the city, so that no time would be given for decomposition. The conduit itself should be smooth, impervious to water, and should be water tight throughout its entire length. It should be flushed at intervals, and so thoroughly that the development of any considerable amount of sewer gas would be impossible. It should be so well ventilated that the small amount of sewer gas which might unavoidably be generated in the sewer would be so diluted with fresh air as to be rendered harmless. It should be provided with ample means for inspection and repair. It should be automatic in its action, so as to require the least possible amount of care and attention. One of the first questions which presents itself to the engineer in planning a system of sewers is, whether the sewers shall be made large enough to carry the storm water as well as the sewage, or the sewage only. When a system of sewers is designed to carry both the storm water and the sewage, it is called the "Combined System." When the system is designed to carry only the sewage proper, that is, the liquid refuse from dwellings, factories, etc., it is called the "Separate System." The Combined System. The large sewers of the Combined System are usually built of brick. The brick being porous, allows more or less of the sewage to escape into the soil, even if every joint is water-tight, which is never the case. The rough surface of the bricks soon become covered with a slime of organic matter, which is constantly decomposing. In designing sewers on this system the size will be determined mainly by the amount of rainfall per hour during storms, and the surface to be drained. The volume of rainfall to be provided for is so much more than the sewage, that the amount of sewage scarcely enters into the computation.* It is readily seen that ordinarily the sewage will be but a trickling stream in a sewer large enough to carry the storm water. At the street corners are catch-basins into which the storm water passes on its way to the sewer. Here the sand and rubbish, carried along by the current from the street, is supposed to settle and remain in the basin, while the water passes through a trap into the sewer. In the rush of water during a storm, however, a considerable quantity of the material which is supposed to remain in the catch-basin is carried on into the sewer, and this, with other foreign substances, introduced into the sewer either by accident or malice, settles on the bottom. These obstructions form a series of small dams in the sewer, and in dry weather the sewage stands in a succession of pools along the sewers, decomposing and sending volumes of sewer gas out of every crevice through which it can escape. The great size of the conduits of the Combined System, it is seen, is detrimental to their efficiency in removing sewage rapidly and completely; and yet, for the purposes for which they are supposed to be designed, they are seldom large enough. Even where vast sums have been spent to construct the Combined System of sewers, it is seldom, if ever, that they will carry the water of great storms. In many cities-notably Chicago and London-where money has been poured out without stint, and millions of dollars have been expended for sewers of great size, the extraordi*See chapter specially devoted to this subject. 1 nary storms are not provided for, and the consequence is that the sewers overflow, and cellars and basements are flooded with sewage. Where the storm water is excluded from the sewers, or only a definite amount admitted for the purpose of flushing, no such disaster can occur. Some have advocated The difficulties of properly flushing and ventilating large sewers are almost insurmountable. Many devices have been proposed for ventilation. high chimneys with a fire in them to produce a draught. Others, a shaft with a screw or fan, for producing a current. None of these plans have proved efficient, and there seems to be no way of disposing of the gas except to let it out into the street by openings from the sewer to the pavement. In any dry season, when there is the least amount of sewage and, therefore, the most sluggish flow and the greatest evolution of gas, the water evaporates from the catch-basin trap and there is nothing to hinder the escape of gas into the streets. The catch-basin itself, unless kept clean, soon becomes a cess-pool, charged with filth from the streets and gutters, which soon decomposes. The flushing cannot be very thoroughly accomplished, owing to the rough interior surface of brick sewers, and to the large amount of water necessary in the large sewers. The most that can usually be done is to produce current enough to carry forward and out of the sewer the solid matter and rubbish, which would obstruct the flow of the sewage. Sometimes the sewage itself is stored up until a sufficient volume is collected to flush the sewer, when it is released. These points are so well brought out in the annual report of O. W. Wight, A. M., M. D., Health Officer, Detroit, Mich., to the Common Council, that we quote quite fully from his report: "Ditches, gutters, tiles and porous brick conduits for removing surface and subsoil water are comparatively cheap. It adds immensely to the cost to trans form water drains into sewers, so as to make them at all fit to convey liquid wastes. The combined expense of a separate drainage system and an independent sewer system, is much less than the expense of a single system that cannot be so constructed as to perform well the double service of removing water from the soil and liquid from habitations. "In most places it is not difficult to find a proper out-fall for the water of a drainage system. As soon as sewage is mixed with the flow of drains the whole mass is contaminated, and the trouble and cost of securing a safe out-fall are, as a rule, greatly increased. The necessity of pumping vast quantities of rain water and subsoil water, mingled with the liquid refuse of houses and factories in the same system in the new sewerage works of Berlin and Dantzic, increases the running expenses to an extent threatening failure. "The sewage proper of a city is nearly a constant quantity. It is approximately measured by the amount of water daily used in houses and factories. Consequently, the engineer in constructing a system for the removal of sewage proper, can adapt it to a constant flow and make it self-cleansing. On the contrary, rain-fall is an immensely variable quantity. A drainage system for its removal must be of maximum size. When sewage, therefore, is turned into the drainage system, a slow flow will be inevitable much of the time, resulting in putrefaction and the generation of sewage gas, the presence of which, within the area of inhabited places, dangerously violates the most vital law of sanitation. "In the drainage system all conduits are purposely made to let water in. The object is to convey water away from the soil But a porous drain will strain sewage through into the earth, and gradually pollute it. Consequently, a conduit for the conveyance of sewage must be made tight. Hence the absolute incompatibility of the two ends sought in the same structure. A good sewer is a bad drain. A good drain is a dangerous sewer. Attempts are constantly renewed to attain the double quality of perviousness from without and imperviousness from within, with unceasing and inevitable failure. Sanitarians who are quacks in engineering have tried it in vain; engineers who are quacks in sanitation have tried it equally in vain. Quacks in both engineering and sanitation, sometimes well represented in City Boards of Public Works, obstinately keep up their search for the unattainable, like the seekers for the philosopher's stone and the inventors of perpetual motion. "Water stored in cisterns is almost invariably poisoned by the way of overflow pipes which discharge into the sewer system of inhabited places and return the dangerous gas. And the drain pipes from cellars and basements generally furnish avenues through which this invisible foe of human life in cities finds easy ingress to habitations. A separate drainage system affords an easy means of guarding against peril from such a source Sanitary inspectors are often astounded by finding a tube from an ice box, in which choice and delicate food, like meats and milk, is kept, running directly into a sewer pipe. The combined sanitary and engineering quack will tell you, with pitiful ignorance, that the deadly sewer gas is kept out by means of a little water-trap through which a baby could blow with a straw. A separate system, used exclusively for sewage, is the only certain safety against such danger. "With the clumsy, costly, perilous Combined System in general use for removing water and sewage together, the earth of towns gradually becomes infected with organic matter in a state of putrescence. Hence the water of springs and wells at length becomes polluted and unfit for use. With a separate, properly constructed and properly managed system of impervious pipes for the removal of all sewage, and with other sound sanitary regulations for the care and removal of solid organic refuse, there is no reason why the spring water and well water in towns should not remain clean and wholesome. Besides, when the earth of inhabited places is kept so clean as to preserve the purity of the water, no exhalations will arise from it deleterious to health and dangerous to life. * * * * * "This is not the place to describe in detail the separate sewer systems for the removal of liquid organic wastes from inhabited places. The engineer must conform to the requirements of sanitary science. Any system will be faulty which allows sewage to putrefy at all, either in its source, on its journey from human abodes, or in its outfall. * The great principle to be kept in view is the removal of sewage (not sewage diluted with vast quantities of surface and subsoil water) without pollution of the soil, without putrefaction, and consequently without generation of sewer gas on the journey. * The soil where man dwells is sacred, and it is sanitary sacrilege to pollute it. He who fouls the air that he breathes himself, or the water that he drinks, or the food that he eats, is a barbarian who might learn wisdom from the cat or decency from any swine not demoralized by contact with man. He who fouls the air that another must breathe, or the food that another must eat, or the water that another must drink is a criminal, to be classed with those who maim and kill. "There are more reasons for such care in the removal of organic wastes from inhabited places than appear on the surface. The chemistry and hygiene of putrefaction are complex, involving many practical considerations. Wherever there is a collection of putrefying organic matter, whether on the ground, in the ground, within a faulty sewer, or under a habitation, there is a tireless foe to health and life. Not only are putrescent collections of garbage, decaying vegetables, manure, offal and human excreta harmful in themselves, by reason of exhalations poisoning the air and leeching liquids polluting the earth; they are also depositories and multipliers of disease germs. Such collections may not produce infectious diseases de novo, but they lessen the vitality of people living in the neighborhood, and thereby lessen the power of resisting epidemics. It is a well known pathological fact that nature struggles to eliminate |