the use of water-closets in all houses, and to furnish a good flushing
for kitchen sinks, &c. A necessary complement of this work--indeed, it
should properly precede it--is the establishment of a system of sewers
by which all of this liquid outflow may be carried safely away. It would
be out of the question in a small or scattered community, especially
where roadways are unpaved, to establish any system which should
include in its working the removal of surface water. The moment we
undertake to make sewers of sufficient capacity to carry away the storm
water of large districts, then we enormously increase the scale and cost
of the work.
So far as the removal of house sewage alone is concerned, the work need
by no means be very costly. If a tolerable inclination can be given to
the line of sewers,--say a fall of one in two hundred,--a six-inch pipe
will have a capacity quite up to the requirements of a village of two
thousand inhabitants using one hundred gallons of water per day per
head. It will, however, be safe to use a pipe of this size only when it
is true in form and carefully laid, so that there shall be no retarding
of the flow at the joints from the intrusion of mortar, or any other
form of irregularity. Unless the joints are wiped quite smooth, the
roughness remaining will serve as a nucleus for the accumulation of
hair, shreds of cloth, and other matters which will hold silt and
grease, and form in time a serious obstruction. Nothing smaller than
six-inch pipe should be adopted for a street sewer. Unless the work is
to be most carefully done, for all but the branch lines, for a
population of five thousand, or less according to the fall of the sewer,
it will be safer to use eight-inch pipes. These pipes must be laid with
great accuracy as to grade and direction. All corners should be turned
with curves of large radius and regular sweep, and with an additional
fall to compensate for the increased resistance of curves. The weight of
the pipe should not be supported upon the sockets (see Figure 3), partly
as a question of strength, and partly because any irregularity of form
or thickness of the socket would change the inclination of the sewer.
The bottom of the trench being brought exactly to the required grade,
let there be dug out a depression greater than the projection of the
socket, the pipe resting upon its finished bottom for its whole length.
(See Figure 4.) Too much care cannot be given to the thorough filling
with cement of the space between the socket and the pipe inserted into
it; the whole circle being well flushed and wiped, so that there may be
no possibility of leakage.
[Illustration: FIG. 3 PIPES RESTING ON THEIR SHOULDERS.]
[Illustration: FIG. 4. PIPES RESTING ON THEIR FULL LENGTH.]
The objection to leakage is twofold: sewage matters escaping into the
soil might contaminate wells and springs; and it would also rob the flow
through the pipes of water needed to carry forward the more solid
contents. The continued efficiency of these small drains for carrying
away the solid or semi-solid outflow of the house is dependent very
largely upon the presence of sufficient water to create a scouring
current. While eight-inch pipes are admissible as a safeguard against
imperfect laying, they are liable to the grave objection, that, where
the service to be performed is greatly less than their capacity, the
stream flowing through them will not be sufficiently concentrated to
carry forward the more solid parts of the sewage. Up to the limit of
their capacity, six-inch pipes properly laid are greatly to be
preferred, as insuring a deeper stream which will more generally attain
the velocity of three feet per second, needed to move the heavier
constituents of the sewage. The difference in cost between six-inch and
eight-inch pipes will be sufficient to cover any extra cost of the most
careful workmanship. However much attention may be given to the
cementing of the joints, it will be impossible to prevent the running
into the pipes of a certain amount of mortar; and the workman should
have a swab or a disk of India rubber of the exact size of the bore of
the pipe, with a short handle attached to its middle, to draw forward as
each joint is finished, and so scrape away any excess of mortar before
it hardens.
Wherever it is, or may probably become, necessary to attach a
house-drain or land-drain, there should be used a length of pipe having
a side branch, oblique to the direction of the flow, to receive such
connection. The location of these branches should be accurately
indicated on the plan; and they should be closed with a flat stone or a
bit of slate, well cemented in place.
It will at times be necessary to use larger conduits than even an
eight-inch pipe. Up to a diameter of fifteen inches, it is cheapest to
use pipes, but for eighteen inches or more, brick-work is cheaper; and
at that size--a considerable regular flow of water being insured--the
slight roughness of brick-work offers no serious objection. The use of
oval or egg-shaped sewers will rarely be necessary under the
circumstances that we are considering; but there may be exceptional
conditions where the covering-in of a brook, or storm-water course,
cannot be avoided; and in such cases the volume of water may vary so
greatly that there will at times be a mere thread of a stream, and at
times a torrent. Here the oval form is the best, as concentrating a
small flow within a narrow and deep channel, and still giving the
capacity needed for exceptionally large volumes. All bricks used for
sewers, man-holes, &c., should be of the very hardest quality, and true
in form. The general rule is to be kept in mind, that the thickness of
the wall of a brick sewer should not be less than one-ninth of the inner
diameter; that is to say, that up to a diameter of three feet the
thickness of the wall should equal the width of a brick,--four inches.
This applies to circular sewers only: the oval form, being less strong,
calls for a wall of a thickness equal to one-eighth of the largest
diameter.
Connecting drains leading from houses to the sewer are to be made at
private cost; but they should be made in accordance with plans furnished
by the public authority, and by a workman acceptable to that authority.
The householder might be permitted to take the responsibility of the
finishing of his drain, but for the fact that the working of the public
sewer calls for the largest amount of water in proportion to the amount
of solid matters that it is possible to secure, and thus makes it
imperative that this drain should be absolutely tight, so that the
liquid parts of the house outflow shall not trickle away through its
joints, leaving only the more solid parts to flow into the public sewer.
Properly graded and smoothly jointed, a four-inch pipe will carry more
water than even the largest boarding-house or country hotel is likely to
discharge. There is, however, a tendency in all house-drains to become
filled in the early part of their course by the accumulation of grease
and solid matters caught in the grease. Where no form of grease-trap is
used, there is a certain argument in favor of the use of six-inch pipes
for the upper part of house-drains. The use of a grease-trap, however,
should always be insisted upon; and with its aid these obstructing
matters will be retained, and the outflow may be perfectly carried by a
four-inch pipe.
So far as the public sewer is concerned, it makes little difference what
is the size of the house connection drain through the greater part of
its course; but the junction with the sewer should, under no
circumstances, where six-inch sewer-pipes are adopted, be more than four
inches. I should even insist on four-inch connections with an eight-inch
sewer. Through neglect, or by reason of improper management, many kinds
of rubbish find their way into house-drains; and a four-inch opening
will admit as many of these into the sewer as it will be able to carry
away. If, by reason of bad construction or neglect, an obstruction is to
be caused at any point, it should be in the drain, which the person
responsible for it must cleanse or repair.
The grease-trap referred to above may be any form of reservoir which
will retain the flow from the kitchen sink until it has time to cool,
when its grease will be solidified, and will float at the surface. The
outlet from this trap should be at such a distance below the surface of
the water, that there will be no danger of its floating matter passing
in with the discharge. A very simple device for this purpose is shown in
Figure 5. From a trap of this sort the flow is constant whenever
additions are made to its contents.
[Illustration: FIG. 5.--GREASE-TRAP. I, Inlet; V, ventilator; O,
outlet.]
[Illustration: FIG. 6.--FIELD'S FLUSH-TANK.
A, Receiver; B, grating; C, ventilator; D, siphon; F, entrance to drain;
I, delivery from sink.]
Figure 6 shows the invention of an English engineer, Mr. Rogers Field,
which has the effect of retaining all of the outflow from the kitchen
sink until it is entirely filled,--say thirty gallons. When filled, any
sudden addition of a few quarts of water, as from the emptying of a
dish-pan, brings into action a siphon whose entrance is near the bottom
of the tank; and this siphon rapidly discharges all of the contents
above its mouth in a flow having sufficient force to carry forward not
only any solid matters which it may contain, but also any ordinary
obstructing accumulations in the drain below. The soil-pipe, carrying
the discharge of water-closets, should not be delivered into the
flush-tank, but at a point farther down the drain, so that any solid
matter it may deposit shall be swept forward by the next action of the
flush-tank. The more often the flush-tank is filled, and the greater the
proportion of its water to its impurities, the more efficient will be
its action. Therefore the slop closet waste leading from the upper
story, and even the outlet pipes of bathing-tubs, may with advantage be
delivered into it.
Although the flush-tank may receive no faecal matter, and even though the
housemaid's sink may not deliver into it, it will contain in the
discharge from the kitchen alone an amount of organic matter which will
produce offensive and dangerous gases by its decomposition. To provide
for the safe removal of these gases, a ventilating pipe should be
carried up to some point not near to any window or chimney-top.
From the time the sewers are ready for service no accumulation of faecal
matter or other organic household waste should be allowed to remain in
the village. All old vaults and cesspools should be filled with earth,
and disinfected by the admixture of lime with the upper layers of the
filling. The use of water-closets in all houses should be made
imperative; and the construction and arrangement of soil-pipes and of
all outlets should be regulated by the health authorities.
It is not worth while here to discuss the details of the construction
of water-closets and other interior plumbing work, except with reference
to soil-pipes and such drains as may deliver the outflow of soil-pipes
to the public sewer. The soil-pipe should be of cast iron, carefully
jointed with lead, not less than four inches in diameter, and carried by
the straightest course possible up through the roof and generally higher
than the ridge-pole. Its open top must not be near any window, and if
within ten feet of a chimney it should be at least one foot below the
level of the top of that chimney. There should be no trap in the
soil-pipe, and no trap in a private drain between the outlet of the
soil-pipe and the sewer. The reasons for this rule are twofold:--
1. No matter what amount of water may be used for flushing out the
soil-pipe, its sides will always be more or less coated with organic
filth; and, however slight this coating, there will be a certain amount
of decomposition. The decomposition of all such matters must be rapid
and complete, not slow and partial. A necessary condition of complete
destructive decomposition is an abundance of atmospheric air to supply
the oxygen which complete decomposition demands. If the soil-pipe is
closed at its top, or if it is obstructed by a trap in the lower part of
its course, there can be no such circulation of air as safety requires.
If there is an opportunity for the free admission of air from the
well-ventilated sewer to feed the upward current almost constantly
prevailing in a soil-pipe open at both ends, the gases resulting from
the decomposition will be of a different and less injurious character
than where the air is confined,--and by the mere volume of air passing
through the pipe they will be so diluted that even were they originally
poisonous their power for harm will be lessened.
The gases formed by the decomposition of organic matter in the sewer
itself, or in the soil-pipe, have a certain expansive force which is
greatly increased by the elevation of temperature, caused, for example,
by the discharge of hot water into the pipe or sewer. If the soil-pipe
is open at its upper end this expansion will be at once relieved; but if
the top of the pipe be closed there will always be danger of the forcing
of the feeble barrier offered by the ordinary water-seal trap of a
branch pipe leading from a wash-basin or sink. Then, too, the
sealing-water of the trap readily absorbs any foul gases presented at
its outer end, toward the soil-pipe, and gives it off in an unchanged
condition at the inner or house end. Such traps retard, but do not
prevent, the entrance of sewer gases into the house. Water-seal traps
which are unused for any considerable time are emptied by evaporation,
and thus open a channel through which the air of the soil-pipe may find
its way into the house.
It is usual in modern plumbing to relieve the pressure of gas in the
soil-pipe by what is called a "stench-pipe." This is a pipe from one to
two inches in diameter, leading from the highest point of the soil-pipe
to the outside of the roof, where it is bent over to prevent the
entrance of foreign matter, or is closed at the top and perforated with
holes to allow the gas to escape. This small stench-pipe is inadequate
for the necessary work. It is very important that there be the freest
possible channel for the movement of air; and nothing will suffice for
this save the continuing of the pipe, at its full size, to its very
outlet. Indeed, angles and bends in a pipe by increasing friction form a
serious obstruction.
The arrangement of the soil-pipe here indicated, although excellent and
efficient, is susceptible of further improvement by the use of a
ventilating cowl or hood at its top. There are many forms of such cowls
in use which are effective whenever there is a sufficient current of
wind; but most of them require a certain force to bring them into
action, and when this force is absent they usually retard the flow they
are intended to increase. This is true of a recent invention known as
"Banner's ventilating cowl," which so long as the wind blows is a most
effective device. When the air is perfectly still, however, it offers by
its curved air-way a certain resistance to the current, and in the case
of baffling winds and flaws the air may blow directly into its opening.
Among the various inventions of this sort nothing seems so free from
objection as the old arrangement known as the "Emerson" ventilator,
shown in Figure 7. This gives a straight outlet, protected by a disk far
enough above it not to prevent its delivery of air; and it becomes an
effective suction cowl, with the least movement of the wind from any
side or from above or below. No eddy caused by the angles of gable
roofs can give it a backward draught; and if a pipe armed with it be
held toward the strongest gale a puff of smoke blown into its other end
will be instantly drawn through. As the patent for this invention has
run out, it is competent for any tinsmith to make it, and it is a common
article of manufacture.
[Illustration: FIG. 7.--THE EMERSON VENTILATOR.]
2. What is said above concerning the ventilation of the soil-pipe from
end to end relates to the interest of the private owner. The interest of
the public gives an equally strong argument in its favor. The sewer
should be as far as possible removed from the condition of an
"elongated cesspool." There must be no halting of its contents, and no
deposit of filth or silt at any point. Within the shortest time
possible, every thing received into the sewer must be passed on and
delivered at its outlet. Still, however perfectly this may be
accomplished, there will always be a certain adhesion of slime to the
walls of the sewer; and this slime must always be in a state of
decomposition, a constant source of offence and possible danger. The
only way to avert this danger is to give the sewer such a thorough
ventilation that the decomposition shall be rapid and safe, and that the
resultant gases shall be at once diluted with fresh air.
This may be measurably accomplished by the simple ventilation of the
sewer itself, through open-topped man-holes; but such ventilation is
less effective in the case of small sewers than of large ones. In the
case of either large or small sewers, it will be vastly increased if we
compel every householder who makes a connection with the sewer, to carry
a drain and soil pipe, nowhere less than four inches in diameter, from
the point of junction with the main line to the open air above the roof.
Where houses are near enough to make the use of a public sewer
advisable, the aggregate of these soil-pipes, having almost constantly
an upward current, will make such a draught upon the sewer, to be
supplied by a downward current through the man-hole covers, as will
maintain a perfect and continuous ventilation.
* * * * *
Important as it is to secure the proper arrangement and construction of
sewers and house-drains, it is still more important to provide for the
safe disposition of the sewage.
We must begin at the outset with the understanding that all sewage
matters not only are of no value to the community, but that it will cost
money to get rid of them.
There is hardly an instance, after all the efforts that have been made,
of the _profitable_ disposal of the outflow of public sewers. The
_theoretical_ value of the wastes of human life is very great, but the
cost of any method for utilizing them seems at least equally great. The
question of cost is so much more important (to the community) than the
question of agricultural value, that the practical thing to do is to
make such disposition as will cost the least, while fully meeting the
best sanitary requirements.
So far as village sewage is concerned, there are three means open for
its disposal: to discharge it into running water or into deep
tide-water, to use it for the surface irrigation of land, or to
distribute it through sub-irrigation pipes placed at little distance
below the surface of the soil. Experiments are being made with more or
less promise of success in the direction of the chemical treatment of
this liquid so as to purify its effluent water, and retain in a solid
form, and in combination with certain valuable added ingredients, all of
its undissolved impurities. None of these processes can as yet claim
consideration in regulating public works.
The cheapest way to get rid of sewage is to discharge it into a running
stream or into tide-water. So far as the community itself is concerned,
this is often the best way; but there will very often arise the
objection that the community has no moral or legal right to foul a
stream of which others make use in its further course. Where the amount
of water constantly flowing is very large, and where the discharge is
rapid,--any given part of the sewage reaching the open air within a few
hours from the time of its entering the pipes,--and where it flows in
moving water for a considerable distance before reaching others who may
have occasion to use the stream, no practical danger is to be
apprehended. But where the sewage is more foul, more sluggish, or
exposed in the open current for a shorter time, the danger may be
serious. The pouring of sewage into tide-water is always admissible
where floats show that there is no danger of a return and deposit of
solid filth; but the delivery at all stages of the tide, in the
immediate neighborhood of salt marshes and mud flats, and in land-locked
harbors, is to be avoided.
Where an unobjectionable natural outflow cannot be provided, the
irrigation of agricultural lands affords the best relief. The action of
vegetation, the oxidation which takes in the upper and well-aerated
layers of soil, and the well-known but not yet fully explained
disinfecting qualities of common earth, are effective in removing the
dangerous and offensive impurities, and in converting them into a more
or less important source of fertility. Precisely how far this system
may be available during winter, it is not easy to say. While the earth
is locked with frost, there must be very little, if any, infiltration;
but, as an offset, the action of a low temperature upon the sewage
matters will clearly be antiseptic; and it is only necessary to provide
against an undue washing away of the surface of the ground during thaws,
and against the flowing of the sewage beyond the proper limits.
Generally in the neighborhood of villages it will be easy to find lands
over which the delivery may be carried on throughout the year without
objection. The sewer, or some form of covered channel, should lead far
enough from any public road to avoid offence. From this point it may be
led by open gutters to the land over which it is to be spread,--or
rather through such a system of surface gutters as will enable us to
deliver it at different parts of the field, according to the
requirements of the crops, and so as to use fresh land at frequent
intervals, leaving that which has been saturated to the purifying
processes of vegetation and atmospheric action.
The gutters having been made, it is easy, by the use of portable
dams,--of thin boiler-iron, like broad shovels,--which may be set in
the course of the flow, to divert the current into any branch channel,
or to stop it at any desired part of this channel. All the gutters
having sufficient descent to lead the sewage rapidly forward, it is
usual to set a dam near the far end of the gutter, and allow the sewage
to overflow and run down over the surface until it has reached as far as
the formation of the ground and the quantity of the liquid will allow it
to spread. This portion having received its due amount of the liquid,
the dam is moved to a higher point, and the overflow is allowed to
spread over a second area. In this way, step by step, we irrigate all
that may be reached by a single gutter. Then the moving of the dam in
the main line turns the water into another gutter, and this is proceeded
with in like manner. In practice it is found best to begin the overflow
at the farthest end of the lowest-lying gutter, working back step by
step until the higher parts of the field are reached. It would be better
that there should be land enough to require the irrigation of any given
area not oftener than once in one or two weeks. The amount required for
a given population cannot be determined by any fixed rule,--so much
depending on the amount of water used _per capita_, and on the
absorptive character of the irrigated soil. In the case of villages, one
acre to each five hundred of the population would generally be found
ample.
There are several instances of the successful use of a much smaller area
than is here indicated, by the use of intermittent downward filtration.
The most noted success in this direction is that at Merthyr-Tydvil in
Wales, a large mining town, where the allowance is only one acre to each
two thousand of the population. There are two filter-beds of light loam
over a gravelly subsoil thoroughly underdrained with tiles at a depth of
six feet. One of these beds is cultivated with some crop like Italian
rye-grass, which bears copious irrigation; and the other by some crop
like wheat, which, in the absence of irrigation, will thrive on the
fertility left over from the previous season. The volume of sewage is
very great, but the action of the six feet of earth in removing its
impurities seems to be complete; the water flowing out from the drains
having been proved by analysis to be really far purer than the standard
fixed by the Rivers Pollution Commission.