THE 
Separate System of Sewerage : 
A Reply to a Paper Published in the Report of the State Board of 
Health, Lunacy and Charity of the State of Massachu- 
setts, 1880, by Eliot C. Clarke, Esq. 
GEO. E. WARING, Jr. 
(Reprinted from the Amercian Architect, March and April.) 
1882. 
NEWPORT, R. I. THE SEPARATE SYSTEM OF SEWERAGE. 
Much the most comprehensive, reasonable and temperate dis- 
cussion of this question, from the adverse point of view, is to be 
found in a paper by Eliot C. Clarke, C. E., Principal Assistant 
Engineer in charge of Improved Sewerage, Boston, published in 
the Public Health Supplement of the second Annual Report of 
the State Board of Health, Lunacy and Charity of Massachusetts. 
As Mr. Clarke, on the whole, favors the combined system, the 
importance of the subject to the general public makes it desirable 
that his argument should be carefully reviewed. He begins, after 
referring to the uncertainty among engineers as to the proper size 
to be given to sewers, by stating the claims set up by those who ad- 
vocate the separate system, and these claims he discusses seriatim. 
(The quotations in this paper, when not otherwise credited, are 
from the document under discussion.) 
“1. The primary object of sewerage the all-important and only 
essential requirement of it —is the removal of sewage proper, 
that is, of water holding in solution or suspension waste organic 
matters liable to decompose and become noxious. All other func- 
tions are comparatively unimportant and secondary and should not 
be permitted to lessen its adaptability to the essential purpose.” 
This does not state the case as I should state it. The primary 
object of sewerage is the removal of fouled waste waters and of sub- 
soil water; that is, of the water which fills the interstices of the soil, 
Avhich finds its way by gravitation into the foundations and cellars of 
houses, which gives an unstable foundation for pavements, and 
which on sloping ground is discharged at the surface. In discussing 
this point Mr. Clarke says: “It is also true that sometimes the re- 
moval of surface and subsoil water is if not an equally essential still 
an essential requirement and both for sanitary and economic rea- 
sons is usually an important function of a sewerage system.” The 
sanitary argument in this case applies almost exclusively to subsoil 
water. He says that sewers are often built into thinly settled 
regions “in order to expedite the removal of rain and soil waters. The Separate System of Sewerage. 
3 
The danger from a damp soil and subsoil is not less real, though 
possibly less in degree and less easily traced to its source than that 
from the proximity of sewage.” This is quite true and is a funda- 
mental basis of all acceptable practice in separate sewerage. He 
then refers to the oft-quoted statement that chemical analysis detects 
little difference in impurity between water-closet matter and sewage 
from which excrement is excluded. Even where excrement is 
withheld from the sewers, kitchen waste is admitted with much 
household rubbish and garbage. The materials thus admitted are 
of precisely the same chemical combination as those which have gone 
into the human system to produce excrement as one of their pro- 
ducts ; and, on their decomposition, they are still substantially the 
same. It is impossible to determine, from the odor, appearance 
or analysis of the contents of an old cesspool whether excrement 
has been discharged into it or not. It is doubtless true, as stated? 
that much horse-manure and other filth is washed into public 
sewers; but it is also true that it ought to be kept out of them, 
and that with proper paving and street cleaning, a safer and more 
profitable disposal of these substances would follow as a matter of 
course. It is, therefore, not in point to say: “ Certainly this first 
portion of rain, loaded as it is with impurities, the droppings of 
animals, and much other organic refuse, is as obnoxious as an equal 
amount of ordinary sewage, and equal care should be taken to get 
rid of it.” It is also not in point to adduce this argument at all 
unless it is a question of ultimate disposal of the wastes of a 
town. Whether this street rubbish is removed by sewers or by carts, 
it had better not be brought into communication with house-drains, 
as it is in the combined system of sewerage. 
“ 2. The amount of polluted water-supply from any district is so 
insignificant in proportion to the quantity of rain-water falling on it 
during rain-storms that sewers designed for receiving storm-waters 
are thereby impaired as to their efficiency for conveying sewage, be- 
cause, being much larger than would otherwise be necessary, the 
depth and velocity of the ordinary flow is less.” This statement is 
too mild. We maintain that storm-water sewers are inefficient for 
conveying sewage for the reason stated, and for the further very im- 
portant reason that they become obstructed with mud, stones, brick- 4 
The Separate System of Sewerage. 
bats, sticks, leaves, and other road rubbish which is washed into 
them through the catch-basins, and that the foul sewage from houses 
is arrested by these obstructions and remains in the sewer to putrefy. 
To equalize the depth and velocity of flow Mr. Clarke suggests that 
the bottom of a large sewer (egg-shaped) may be given the same 
radius as a pipe sewer. This would, of course, give the same depth 
to the ordinary current of house sewage, provided the obstructing 
materials above referred to as coming from the streets can be ex- 
cluded, which, in the combined system, they are not and cannot be. 
He says : “In order that the floating bodies may not strand, the 
centre depth should probably be at least three inches.” This de- 
pends on the diameter and inclination of the sewer. In a six-inch 
pipe laid on an inclination of 1 in 250, where the ordinary flow near 
the upper end, when a bath or water-closet is discharged, is found in 
practice to be less than half an inch deep, some solids brought into 
a sewer by such a stream are stranded. Such stranded bodies are 
carried forward by a discharge from a flush-tank or otherwise which 
increases the depth of flow to one inch (I speak from observation, 
not from actual measurement). After the point is reached where 
the constant flow is an inch deep, there seems to be no stranding of 
matters delivered into “ separate ” sewers. In a “ combined ” sewer 
constructed with a lower cross section equal to that of a six-inch 
pipe, the rubbish brought to it from catch-basins would doubtless 
require the full three-inch stream prescribed and more. This differ- 
ence is a constant one as applied to the two systems, and its collat- 
eral relations have a bearing on other important elements of the 
discussion. It seems to me that Mr. Clarke has made the mistake 
of assuming that the substances to be flushed out of the sewers are 
the same in both cases, and that in both cases the same flushing 
force is required. 
Much importance is attached in his argument to the fact that large 
sewers of low grade will, during heavy storms, run half full, and 
that such a flow will flush them completely. This is true; but it is 
also true that at the tail of the storm fresh obstructions come in from 
the street, that such cleansing storms occur but rarely, that, even 
for many weeks together, there is an increasing accumulation in 
storm-water sewers of putrefying substances awaiting removal, and The Separate System of Sewerage. 
5 
that these in the mean time undergo an offensive and dangerous de- 
composition. Such decomposition results from a radical and inadmis- 
sible defect in every sewer in which it takes place. If anything ap- 
proaching sanitary perfection is to be hoped for, this condition must 
be rendered impossible. Organic wastes lodging in the sewer must 
be swept clean out of it within twenty-four hours or less. If left 
for a longer interval they begin to do mischief. If removed within 
this interval they are of no consequence. This proposition, I think, 
will be accepted by all sanitarians as a sound one. The conditions 
indicated may be secured with the largest combined sewers as com- 
pletely as with separate sewers; but in the one case we need a 
trifling amount of water sufficient to transport what enters the 
sewers from the water-closets and kitchen sinks of a house; in the 
other we need the great volume necessary to fill the sewer to such a 
height as to secure a cleansing velocity not only with reference to 
household wastes, but with reference also to the sticks and stones 
and rubbish washed in from the streets, some of which generally fail 
of removal, even during storms, and remain to accumulate organic 
matters in greatly increased quantity. For the efficient performance 
of the necessary service in the case of large combined sewers, we 
need more water than it is practicable to use. 
Reference is made to the analysis of the atmosphere of a foul 
sewer in Boston which failed to detect a dangerous degree of pollu- 
tion. This point will be referred to hereinunder in connection with 
Mr. James T. Gardiner’s report to the State Board of Health of 
New York. Concerning the evidence of this analysis and other 
points which it is assumed that “some zealous advocates of the com- 
bined system ” might raise, Mr. Clarke says: “ these arguments 
have considerable force; and the answer to them is that, however 
slight the risk from deposits in sewers may be, still as it is a risk 
affecting health and even life, it is not right to impose it upon a 
•community if it can be avoided.” It can be avoided. 
The opinion is expressed that the daily flushing practised with 
the Memphis sewers, “ as it is equally adapted to large as to small 
sewers, may wisely be adopted for sewerage systems constructed on 
the combined system.” It is not equally adapted to the combined 
system for reasons fully set forth above. 6 
The Separate System of Sewerage. 
“3. The small sewers of the separate system are more easily 
cleansed by flushing.” Mr. Clarke enumerates as the substances which 
need to be flushed out of sewers, household refuse of various sorts, some 
manufacturing refuse and fine sand, which works its way through joints. 
In addition to these in the combined system, “ road detritus, gravel,, 
leaves, twigs of trees,” etc. He describes the action of the flush-tanks 
at Memphis, and says that “ if, instead of these six-inch sewers, larger 
ones for rain had been built on the same inclinations and with their 
bottoms shaped like those of the six-inch pipes, the same quantity of 
water applied in the same manner would have produced a precisely 
similar effect.” In this he overlooks the added matters to be flushed 
out in the case of sewers connected with streets which, it is fair to 
presume, would prevent “ a precisely similar effect.” He shows that 
a flushing velocity may be produced in a twelve-inch pipe at a depth 
of three inches, with a moderate increase in the amount of flushing- 
water, and that this effect may be produced at a somewhat lower in- 
clination. He does not say that the effect would continue for so 
great a distance,—and it would not. He says that at the usual in- 
clinations twelve-inch pipes have the great advantage over six-inch 
pipes, that, by increasing the quantity used until they are made to 
flow half full, a flushing velocity may be secured with slopes about 
one-third as steep. The amount of water needed will be about four 
times as much, and where economy of water is important the flush- 
tanks may be worked with sewage. All tiffs is true; but the point 
at which the ordinary flow of house-waste would have a sufficient 
depth to carry ordinary solids would in the twelve-inch pipe be re- 
moved to a very much greater distance, and the quadruple quantity 
of flushing-water delivered at the head of the sewer would have lost 
its flushing effects long before this distance was passed. He says that 
sewers may have their flow dammed back by gates to the height 
of the house-drains, but not much higher, for fear of setting back 
the sewage into cellars, and that, therefore, the larger the sewer, the 
greater the flushing head. This does not necessarily hold, for if the 
small sewer is laid at the same depth as the large one, its flow may 
be dammed back even into man-holes and house-drains to the same 
height above the grade, as in the case of the large sewer. That is, 
it is not the diameter of the sewer, but the distance between the bot- The Separate System of Sewerage. 
7 
tom of the sewer and the level of the cellar which regulates the flash- 
ing head. It is true that flushing by this means will act for a shorter 
time and for a shorter distance (below the gate) because of the less 
quantity of water retained; but it is also true that the occasion for 
flushing is less with the separate sewer than with the combined one.. 
He says: “ After placing a dam in either sewer, on removing it the 
sewage accumulated in the larger sewer falls four times as far, and is 
opposed by only one-fourth as much surface in proportion to the am- 
ount of falling water, as in the smaller one. Neither the main nor 
the branch sewers, therefore, of a separate system can be as effect- 
ively flushed as the larger one of a combined system.” This assumes 
that the head must be regulated by the diameter of the sewer. As 
it is to be regulated by the difference of elevation between the sewer 
and the cellar it does not hold. The main and lateral sewers of the 
separate system require much less flushing than do those which receive 
street rubbish, and they can he as effectively flushed as the larger ones. 
Referring to the use of the “ pill ” he says : “ This method is said to 
have worked well, both in large siphons and in pipe-sewers, but it 
has hardly been in use long enough to afford definite conclusions as 
to its general applicability and effectiveness. It is equally adapted 
to the sewers of either system.” This method is said to have worked 
well by all who have tried it, including Belgrand who used it in the 
Paris siphons years ago, Major Humphreys, who has used it regu- 
larly in Memphis, and Mr. Fowler, who has adopted it as a main re- 
liance in the flushing of the sewers of New Haven. Simple devices 
demonstrate their efficiency at once, and this system of cleansing 
circular sewers has been in use long enough to demonstrate its effi- 
ciency. The demonstration is instant. One need only to observe it 
once to be convinced of its utility. It is not equally adapted to com- 
bined sewers although used with them, because these much oftener 
contain solid obstructions which require the pill to be helped in its 
passage. Among the substances causing obstructions in sewers, Mr. 
Clarke mentions those which catch on projecting pieces of cement; in 
pipe-sewers with gasketed joints, as in Memphis, there are no such 
projecting pieces of cement. In all my experience I have known of 
no instance in which grease runs in a liquid state “ a hundred feet or 
more” to congeal on reaching the sewer. In the discussion on 8 
The Separate System of Sewerage. 
Odell’s description of the Memphis work at a meeting of the Ameri- 
can Society of Civil Engineers, the distance to which grease passes 
in the house-drain before congealing was limited to a few feet. 
“ If the sewers are large enough to enter, that is over two feet in 
diameter, there is little difficulty in removing obstructions; if smaller 
the work must be done by means of rods and chains, pushed or drawn 
from one man-hole to another, at an expense many times greater than 
that of flushing. In either case the work will be more easily accom- 
plished in the larger sewers of the combined system.” From a re- 
port of the discussion of the Memphis system at the meeting of the 
Sanitary Institute of Great Bx-itain, 1880, I quote the following as to 
the remarks of the President of the Engineering Section, Robert 
Rawlinson, Esq., C. E.: 
“ They were told by one of our present great engineers that sew- 
ers should be large enough for men to get into to clean them out. 
Well, all he could say was, that the Legislature had passed a law to 
prevent boys going up chimneys, and he hoped a law would be passed 
to prevent men from going into sewers to clean them out. He, for 
one, would not have the blood of men who were killed in this work 
upon him. He mentioned instances of places sewered on the princi- 
ple laid down in the paper with marked success. He moved a vote 
of thanks to Col. Waring.” 
“4. Large sewers develop and contain a greater quantity of 
noxious gas than small ones, and are not so easily ventilated.” 
This would be properly stated if the expression were “ small 
flushed ones.” Mr. Clarke bases his argument in opposition to this 
statement on the fact that the objection to sewer-gases, or rather 
their offensiveness, depends on concentration, large sewers having an 
advantage over the small ones because of the larger volume of air to 
be contaminated by a given amount of exhaling surface. This would 
be correct if both sewers were closed. Supposing both to be venti- 
lated by the same openings, it would then be rather a question of the 
rapidity with which the whole atmosphere of the sewer is renewed, 
and this certainly must be greater with small sewers than with large 
ones. “It is possible that small sewers may be more easily ventila- 
ted than large ones, but there has been little experiment to verify 
theories on this point.” He seems always, when the indicated proba- The Separate System of Sewerage. 
9 
bilities are not favorable to large sewers, to fall back on the shortness 
of time during which experiments opposing his theory have been car- 
ried out. There has been ample experience during many years to 
show that clean, small sewers, often clean because small, contain 
a much less offensive atmosphere than do larger ones. The sewers of 
Memphis have now been in use for two years; for nearly this period 
they have been very largely used. There have been frequent occa- 
sions, as in making new house-connections, to open them, and the con- 
dition of their air is perfectly known to all who have had to do with 
them. From the “ sewer-gas ” standard they are absolutely pure. As 
they carry offensive matters, they have, of course, a perceptible odor ; 
but in no part and under no circumstances do they give oft the least 
odor of decomposition or anything even suggesting the smell of an 
ordinary sewer. That the system of ventilation through soil-pipes, 
which is there universal, would enormously modify the atmosphere 
of any tolerably clean sewer is undoubted. Mr. Clarke says that 
such ventilation “is not usually considered good practice.” In this 
I cannot agree with him. For the sake of the house-pipes themselves 
as well as of the sewers, I think it is easily demonstrable that such 
thorough ventilation is always desirable. 
New light has been directed to this question by the report of Mr. 
James T. Gardiner, Director of the New York State Survey, and 
member of the State Board of Health, who considers the question in 
the light of recent physiological investigations. He says, speaking 
of storm-water sewers: 
“ The storm-water falling per hour in violent rains over an acre of 
closely built up city land is nearly fifty times the amount of the waste- 
water and sewage produced per hour on the same area. The sewage is, 
therefore, ordinarily a mere trickling thread in the bottom of a sewer 
large enough to carry off great bodies of storm-water. In time of rain 
the sewer will be nearly or quite full of diluted sewage, which is ab- 
sorbed by the bricks, and leaves a coating on them as the water falls. 
The powerfully flowing stream of storm-water on subsiding deposits silt 
in the bottom of the sewer, which obstructs the flow of sewage, giving 
it time to decompose. Foul gases are then emitted, and it has been 
popularly assumed that these gases, called ‘ sewer-gas,’ are the cause of 
disease. 10 
The Separate System of Sewerage. 
“ Physicians are agreed upon the fact that air from sewers passing 
into a dwelling is very likely to produce serious disease. That this ill- 
ness is due to a gas from decomposing sewage is a mere assumption un- 
supported by proof. But the hypothesis was hastily adopted by engin- 
eers, who naturally inferred that the healthfulness of large sewers 
would be secured if they could only drive out or sufficiently dilute this 
gas by ventilating the sewer, or prevent its formation by keeping the 
stream of sewage flowing uninterruptedly. The discussion of the sub- 
ject by Mr. Eliot Clarke, in the Massachusetts Board of Health report, 
and the opinion of other engineers who favor large sewers, seem to be 
based on this idea. 
“ It is time, therefore, to call attention to the fact that no such gas as 
‘sewer-gas’ exists, and that there is absolutely no proof that the diseases 
which attend the admission of sewer-air into a dwelling are produced by 
gases. On the contrary the whole tendency of modern investigation is 
to show that the zymotic diseases are produced by bacteria, whose germs 
are developed under favorable conditions. It is well known that the 
most favorable conditions for the growth of these low organisms are 
heat, moisture, darkness, and the presence of ammonia. The damp walls 
of sewers present, therefore, all the requirements for a most flourishing 
growth of bacteria, whose germs may float off on the sewer-air and be 
carried into dwellings by mechanical action, as dust is borne on any air 
current. 
“It is, therefore, most probable that sewer-air brings the germs of 
disease into dwellings as dust is blown into the window. The foul 
gases of decomposition may or may not be present, The fatal power 
over life lies, probably, in the little plant-seed, odorless and invisible, 
floating upon the sewer-air. 
“ Large sewers are, then, plantations for the propagation of deadly 
organisms, the moist, porous walls forming most favorable soil, the am- 
monia of sewage supplying the manure essential to full development, and 
the warm, damp air stimulating to the utmost all processes of growth. 
“ The occasional flushing of sewers, while it may clear out silt and 
accumulated filth, and thus decrease the amount of heat and ammonia 
from decomposition, can never prevent the growth of bacteria on the 
sewer walls, nor will ventilation prove efficient. Every device of en- 
gineering has been exhausted to keep large sewers clean and well ven- 
tilated, but the air from them is still deadly. Experience, therefore, 
teaches that there is some radical defect in the system of large or com- 
bined sewers, while modern investigations of the origin of zymotic dis- The Separate System of Sewerage. 
11 
eases and the mode of growth of bacteria seem to show that sewer- 
walls are almost ideal hot-beds for the production of fatal organic 
germs. Perfect plumbing may prevent sewer-air from entering dwell- 
ings, but perfect plumbing will always be the rare exception. 
“ In view of these facts I am forced to conclude that from a sanitary 
point of view the combined system of sewerage is a failure. 
“ I visited in London the sanitary department of the Local Govern- 
ment Board which has general supervision of the sanitary affairs of 
England. The Chief Engineer, Mr. Robert Eawlinson, C. E., and the 
principal medical inspectors, Dr. Ballard and Mr. Eadcliffe, are per- 
fectly agreed that the combined system of sewers is radically defective 
from a sanitary point of view. In this opinion Dr. Richardson and. 
other prominent sanitarians concurred. At the meeting of the British 
Association for the Advancement of Science, in York, the leading civil 
engineers whom I met had abandoned their belief in the ‘ combined’' 
system of sewers, being convinced that it could not be made healthful. 
“While all were agreed as to the failure of the ‘ combined system/' 
some of the medical men favor the general introduction of the ‘ pail 
system’ of Manchester of ‘dry removal’ of the excreta in tubs, and 
the use of sewers entirely disconnected from dwellings, to carry off 
only waste and storm-water; while Mr. Eawlinson and other engineers 
advocated water carriage by the ‘ separate system.’” Referring to the 
Memphis sewers, he says : “ The sewers being so small and so well filled 
by the flow of sewage there is very little exposed wall-surface on which 
bacteria can germinate, and very little space for storing up germ-laden 
air. The gases and heat of decomposition, which so powerfully stimu- 
late the growth of organic life, are prevented by thorough daily flush- 
ing, which is only possible in small sewers. The smooth glazed surface 
of pipes is unfavorable soil for vegetable growth, compared with po- 
rous bricks moistened with sewage. 
“It will therefore be seen that the separate sewers do not afford those 
favorable conditions for an extensive and rapid growth of bacteria 
which are the fatal defects of the large combined sewers. The smaller pipes 
move rapidly all sewage from dwellings, without connecting them with 
foul caverns whose sides produce low organic life. Where the separate 
system, with flush-tanks, is in operation, I can learn of no complaints 
of ‘ sewer-gas.’ 
“The ‘ separate system’ is therefore greatly to be preferred for sani- 
tary reasons.” . . . 
“Although a number of English towns have wholly or partially 12 
The Separate System of Sewerage. 
adopted a separate system, and the results have been so good that the 
engineers of the Local Government Board advise its general use, yet I 
was informed by the Chief Engineering Inspector, Mr. llawlinson, that 
nowhere in England had the separate system been so completely devel- 
oped and applied as in America, in the city of Memphis. He assured 
me that English engineers and sanitarians were watching with great 
interest the working of the Memphis sewerage, considering its results 
to be a thorough test of the principles involved. 
“ On further investigation of the small sewerage plans of Oxford and 
Hover, which I visited, and other English towns where modifications of 
the separate system are in use, I wras confirmed in the opinion that the 
separate system of Memphis, designed by Col. George E. Waring, Jr., 
is much the most thorough and complete which has yet been built on a 
large scale. Instead, therefore, of describing imperfect English exam- 
ples of the system, which, although great improvements over the com- 
bined sewers, are inferior to the American plan, I shall give the results 
of a recent examination of the Memphis sewerage, made for the city of 
Baltimore by Mr. C. H. Latrobe, C. E., a copy of whose report to the 
mayor and city council I have just received.” Then follow's the sub- 
stance of Mr. Latrobe’s report, including the following : 
“ In summing up my impressions as to the separate system as devel- 
oped at Memphis, I would say that it is well planned and well executed, 
and fully answers the purpose for which it wTas intended and which I 
conceive to be primarily the object of all sewerage, viz.: to carry off 
all human and industrial waste with rapidity and cleanliness to its ulti- 
mate destination. 
“ The accompanying system of tile-drains has also thoroughly drained 
(as far as I know) the very tenacious subsoil of the city. As to the 
storm-water at Memphis, it can safely be left, from all I learn, to take 
care of itself.” Mr. Gardiner concludes thus : 
“ I am of the opinion that the separate system of small sewers avoids 
in great measure the inherent sanitary difficulties of the combined plan; 
and that it is an efficient and economical method of removing the sew- 
age of towns. I therefore recommend the State Board of Health to 
advise the adoption of the separate system of sewage in those towns 
which have asked for information on this subject.” 
Acting upon his report the State Board of Health at its last quar- 
terly meeting passed a series of resolutions, including the following: 
“ 6. That towns having proper water-supply should be provided with 
a system of small sewers adapted to carry only sewage, including ex- The Separate System of Sewerage. 
13 
creta, slops, and waste-water, and excluding storm-water, which should 
be taken care of separately. 
“ 7. That the costly plan of large combined sewers for carrying sew- 
age and storm-water together has proved a sanitary failure both in 
England and in this country; while the ‘separate system/ when prop- 
erly constructed, avoids in great measure the evils from sewer-air, now 
so common, and is much less expensive for most towns. 
“8. That the ‘separate system of sewers/ with flushing-tanks, is 
hereby recommended for general use in this State.” 
“5. So much smaller sewers will suffice to carry off the sewage 
only, that their cost need be but a fraction of what would be required 
to build sewers admitting rain; and by adopting the former many 
towns can avail themselves of the benefits of sewerage which would 
otherwise be debarred from it on account of the expense; and in any 
case the difference in cost would be considerable.” 
Mr. Clark admits that “ the first cost of a system for sewage alone 
will be much less than that of one admitting rain.” He states the case 
very fairly in comparing the cost of the sewers of Chicago with those of 
Memphis, and says: “It appears that the first cost of the combined 
system will be two and one-half times that of a separate system not 
admitting rain.” In my own judgment the average difference will 
be more than this. He thinks, however, that the question of econ- 
omy depends upon other considerations which he enumerates, some 
of which are sound and some are not so. As for example, he 
charges the separate system with “ all pecuniary damage caused by 
lack of prompt removal of the rain-water, especially the damage to 
street surfaces which would be gullied and washed away in time of 
rain.” Such washing is of rare occurrence and is so seldom expe- 
rienced, even in Baltimore, where the surface flow is copious and 
rapid, that an influential portion of the public have long objected to 
the adoption of a sewerage system for that city because it would de- 
prive them of the efficient cleansing of the streets by storm-water> 
which they have always found so satisfactory. He does not charge 
the combined system with the flooding of cellars, and often of streets 
and yards by overflows, caused by the gorging of the sewers, during 
storms, nor does he refer to what is much more serious than cost and The Separate System of Sewerage. 
what often happens under such conditions, the flooding of base- 
ments and cellars with filthy sewage. 
“ 6. Rain-water in excess is seldom worse than inconvenient, and, 
at most places, can properly be allowed to flow off over the surface 
of the streets, as it does everywhere before the introduction of 
sewerage." 
I should make this stronger and say that storm-water may be 
allowed to flow off over the surface of the street with great advantage 
so long as it does not accumulate to a dangerous extent. He says : 
“ It is begging the question to claim that since the rain flowed over 
the surface everywhere before the introduction of sewerage, it can 
continue to do so ; for the same sort of reasoning would apply to the 
sewage itself.” This is true only if there is no difference between 
running storm-water and foul sewage over the surface. It seems 
to me a novel view of the subject for a modern sewerage engi- 
neer to entertain. He says of rain-water that it is a question how 
far it can be made to flow in the streets without becoming “ too great 
a nuisance." That is the precise limit to be adopted. My idea 
would be to keep it in the streets until it does become too great a 
nuisance, and then to carry it underground. It will be found in 
practice that the area over which water may be kept on the surface 
is so great that with proper arrangement the underground storm-water 
channels will be so much reduced in extent that it is not fair to call 
them “ a second set of sewers,” which is a favorite expression with those 
who argue against the separate system. He refers to the complaint of 
residents “ that the amount of water on the street in time of heavy rain 
or thaw is a nuisance.” But he says that residents are too often ex- 
acting in matters concerning their comfort. He does not refer to the 
more frequent and much more serious complaint of residents whose 
houses are near catch-basins, almost invariably offensive; but he 
does say; “ In the latitude of Massachusetts catch-basins also some- 
times freeze up and cause trouble, but this can be prevented, or they 
can be thawed out with salt.” 
He refers to the fact that the grading of the surface of streets and 
the elevation of yards as compai’ed with the streets must be modi- 
fied if storm-water is to flow over the surface. This is often entirely 
true, and so far as it goes, it is an argument against the separate system The Separate System of Sewerage. 
15 
of sewerage. It is, however, a putting of the question of the cost of 
grading and of convenience into opposition with the vital question of 
the public health. 
“7. Where it is absolutely necessary to remove the rain as 
well as the sewage by means of underground conduits, two sets of 
sewers can be built, each designed for its special purpose, and the 
greater efficiency of both will compensate for the slight increase in 
cost.” 
In this statement I only object to the expression “ two sets of 
sewers.” As stated above, the storm-water Jsewers would only 
be main outlets for various districts chiefly drained of their rain-fall 
by surface flow. Mr. Clarke says: “To build a separate set of 
sewers for this alone presents no especial difficulty. The sewers 
must be as large as if intended to convey the sewage also : therefore 
if they were placed equally low, the cost of a double system would 
be two-fifths greater than that of a combined one.” It would be so if 
the storm-water sewers reached everywhere that the separate sewers 
do, and as stated if they were placed equally low. In practice their 
length would probably average not more than one-fourth of the 
length of the small sewers, and as complete drainage of the soil of 
cellars and of houses would be effected by the pipe sewers and their 
accompanying tile-drains, the necessary storm-water conduits need 
be carried only sufficiently under the surface to be out of the way, in 
many cases three feet deep instead of thirteen feet deep. Con- 
structed on this principle, “ the two sets of sewers ” could not “ in- 
terfere with each other as to position, and where they cross each 
other as to their grades.” He says : “ The small sewers would lack 
the periodical flushing by rain-water, and during a very light rain of 
short duration considerable street-refuse may be carried into the 
large sewers to remain and decompose until the next shower; but 
as these sewers would not be connected with the houses, this would 
cause no danger, and, if they were well ventilated, little annoyance.” 
The Memphis sewers have no “ periodical flushing by rain-water,” 
but a copious flushing every day by automatic flush-tanks. The 
street-refuse if carried into combined sewers and remaining to de- 
compose, the sewers being connected with the houses, the immunity 
indicated would not exist. 16 
The Separate System of Sewerage. 
“8. Where the sewage must be raised by pumping, or treated in 
any way, these operations can only be satisfactorily accomplished 
if the sewage is unmixed with rain.” Mr. Clarke says that where 
pumping is resorted to a separate system becomes a necessity. For 
towns discharging their sewage by gravitation, he indicates the use 
of intercepting sewers large enough for the dry-weather flow, 
with independent storm-water overflows. He does not pretend that 
this is more than a makeshift. 
“ The result of this discussion appears to show that a separate 
system of sewerage is only necessary where cellars are so low that 
they must be drained by pumping; that in other cases its only merit 
is its cheapness; that the saving in first cost of sewers will be about 
three-fifths, depending on the character of the soil; that the final 
economy will depend on circumstances ; that the system would only 
be advisable where the branch sewers could incline not much less 
than one in one hundred ; that surface-drainage for rain is attended 
by a varying amount of inconvenience and damage which increases 
with the growth of a town.” 
My own conclusion would be this: The result of this discussion 
appears to show that a separate system of sewerage is necessary 
where cellars are so low that they must be drained by pumping, 
and where the cost of a combined system cannot be afforded; that 
its economy is always very great; that it is entirely efficient with a 
fall of one in five hundred; that surface-drainage can be prevented 
from causing inconvenience or damage worth considering, no matter 
what the size of the town, for an outlay which compared with the 
extra cost of a system of combined sewers would be trifling; and 
last and most important, that while combined sewers cannot possibly 
meet the necessary sanitary requirements, separate sewers can be 
made absolutely safe, affording the only means now known for the 
perfect sanitary drainage of a town of any size, and that for these 
reasons the separate system is always advisable. 
His conclusion is thus stated :