SEWERAGE SEWAGE HBHT PURIFICATION

SEWERAGE SEWAGE HBHT PURIFICATION
VAN NOSTRAND SCIENCE JERI ES.
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f.*rict;.&Q
jiff,
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SEWERAGE
SEWAGE
AND
PURIFICATION
BY M.
N.
BAKER,
PH.
B.,
C. E.
ASSOCIATK EDITOM, * ENGINEERING NEWS.'*
JOINT AUTHOK u SEWAGE DISPOSAL /.N THE UNITED STATES.'
AUTHOR "SF.WAGE PURIFICATION IN AMERICA,"
isH SEV/A<;E V.'ORKS."
Fifth Edition,
HBHT
UC-NRLF
Revised and Enlarged.
157
.
D,
r
VA]N
NEW YORK:
XOSTRAND COMPANY,
Park
1913
Place.
THE
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SEWAGE DISPOSAL
IN
THE
UNITED STATES.
BY
GEO. W. RAFTER, M. Am.
AND
M. N.
BAKER,
Soc. C. E.,
Ph.B.,
ASSOCIATE EDITOR "ENGINEERING NEWS."
Large
Svo, 600 pages, 7 plates, 116 illustrations
in
tJie text.
Part I. of this great work discusses the principles of
the subject in detail, citing foreign experience where
it will throw light upon the subject, but
dealing chiefly
with American ideas and practice, and with the broad
principles of sewage purification, or other means of
disposal, which are more or less applicable everyEach method of purification is discussed at
where.
length, and many allied subjects never before treated
in a comprehensive manner are taken up.
Part II. is an exhaustive description of about forty
sewage purification plants as actually built in the
United States and Canada, with
many
details of cost,
methods of operation and the results obtained in actual
Several appendices give English and Amerpractice.
ican Statute Laws regarding stream pollution and its
prevention, and the duties and powers lodged in State
Boards of Health for the preservation of the purity of
inland waters, especially where used for public water
supplies.
SENT POSTPAID ON KKCEIPT OF $6.00 BY THE PUBLISHEBS,
D.
VAN NOSTRAND
CO.,
NEW YORK
CITY.
25 PARK PLACE,
SEWERAGE
SEWAGE
AND
PURIFICATION
BY M. N. BAKER, PH.
B., C. E.
ASSOCIATE EDITOR, "ENGINEERING NEWS."
"SEWAGE DISPOSAL IN THE UNITED STATES.'*
AUTHOR "SEWAGE PURIFICATION IN AMERICA,"
"BRITISH SEWAGE WORKS."
JOINT AUTHOR
Fifth Edition,
B,
Revised and Enlarged.
NEW YORK:
VAN NOSTRAND COMPANY,
.
?5
Park
1913
Place.
COPTBIOHT,
BY
D.
1905,
VAN NOSTRAND COMPANY.
^IK Rights Reserved.
PREFACE.
One
of the earliest volumes in this series
was "
Sewerage and Sewage Utilization," by
W. H. Corfield, of the UniverLondon.
of
Appearing in 1875, when
sity
American
cities had sewscore
a
few
only
and when
the
name,
erage systems worthy
was
nractically unsewage purification
known in this country, the little book was
Professor
and for many years continued
to be of great
service this side the water.
When, after twenty years, the publishers
requested the author to revise the book, he
found revision, or even re-writirg, entirely
out of the question, so ill-suited were
its
matter and method to modern American
conditions.
There being a strong demand for a brief
but comprehensive book on the subject, it
was decided that an entirely new one
should be written.
Professor Corfield entitled his discussion
365610
TV
"
Sewerage and Sewage Utilization."
The
" Purificapresent author prefers to use
"
rather
than
tion,"
Utilization," in his
In making this change he does not
wish to detract from the importance or
possibilities of utilization, but simply to
title.
put purification, or the sanitary problem,
commercial
first, and utilization, or the
problem, second. In addition, utilization
is
only one of several processes of
purifi-
cation.
There are now in the United States some
fifty cities and villages, many institutions,
manufactories and houses, employing one
or another system of sewage purification.
studies of the Massachusetts State
The
Board of Health have given an impetus
to
intermittent filtration of late, but chemical
precipitation is practiced in
and broad
pecially in
many
places
common, esthe West, where " Water is
irrigation
is
King," and the sewage
quite
is
used for plant
drink rather than plant food.
It is
hoped that this little book will be
some engineers, especially those
of use to
whose practice has been
in other lines of
V.
engineering, and to that vast and rapidly
growing body of sewer commissioners and
superintendents, boards of public works,
boards of health, mayors and city council-
men, and public
spirited citizen in general,
are of late taking a growing
and most promising interest in sanitary
all of
whom
problems.
M. N. B.
104 Tribune Building,
New York, Dec. 31, 1895.
PREFACE TO THE SECOND
EDITION.
In the nearly ten years that have elapsed
since the appearance of the first edition of
this little book, the newer and so-called
sewage treatment
have been announced, passed through an
bacterial processes of
experimental stage and come into extensive
Meanwhile the author has improved
many opportunities to visit American sewuse.
VI.
age purification works, old and new, and
during 1904 spent several months abroad,
chiefly in Great Britain, visiting sewage
works and meeting a number of the men
prominently connected with British progress in this field. As a consequence of
the events named above, the section of this
book which deals with the purification of
sewage has been largely rewritten and
somewhat extended. Few changes in the
other section, on sewerage systems as contrasted with disposal works, have been
deemed
necessary.
M. N. B.
220 Broadway,
New York, May
5,
1905.
CONTENTS.
Page.
Sewerage System is Needed
The Value of a Sewerage System
Good Engineering Advice Essential.
Preliminary Reports and Plans
Why a
Separate or Combined System
Subsoil Drainage
14
15
21
25
28
Final Disposal of Sewage
Population, Water Consumption,
Sewage, Rainfall
5
12
Volume of
Method of Meeting the Cost
Design and Construction of the Conduit
System
Manholes
Sewer Grades
Flushing Devices
Y-Branches for House Connections
Ventilation of Sewers
34
46
58
63
64
64
66
68
Misapprehensions Regarding So-called Sewer
Gas
72
Dr. Billings' Opinion on Sewer Air and Ventilation
74
Features Peculiar to the Combined System..
Oatch Basins or Rainwater Inlets
80
Storm Overflows
81
77
vm.
Page.
Pumping
Stations, Keceiving Reservoirs
and
Force Mains
82
Tidal Chambers
84
Final Plans and Specifications
Securing Bids and Awarding Contracts
The Proper Lxecution
.
of the Contract
Operating the System
8i
86
90
92
Sewarge Commission, Board of Public Works
or City Council
Sewage
93
Purification in its General Aspects....
Sedimentation
Mechanical Straining
Chemical Precipitation
The
Septic Tank
Artificial Aeration.
" Electrical" Processes.
95
104
106
108
116
121
Broad Irrigation or Sewage Farming
125
Sub-Surface Irrigation
131
Intermittent Filtration
131
Contact Beds
Percolating Filters
142
147
Sewage Purification Plants not Nuisances
Status of Sewage Purification....
150
The Present
140
SEWERAGE AND SEWAGE
PURI-
FICATION.
WHY A
SEWERAGE SYSTEM
is
NEEDED.
An abundant supply of pure water is
one of the greatest advantages which any
community can possess. This is so generally recognized that every
American town
with a population reaching into the thousands has, or is planning to obtain, a public
Such a supply having been
through the streets
and houses, used and enjoyed, what dispo-
water supply.
distributed
secured,
be made of it ? Obviously
may be the very reverse of its
sition shall
its
removal
in-
troduction.
As
it
was'distributed through
a network of conduits diminishing in size
with their ramifications, so it may be collected again by similar conduits, increasing in size, as one after another they unite
in a
common
volume
The
is
But the outgoing
from the incoming.
was pure and limpid the
outlet.
far different
influent
;
effluent has
been fouled in performing the
demanded of it, and should it accumulate and remain at any point it
would decompose and give rise to offensive
services
odors.
Moreover, in
various fields of
its
usefulness, the once pure water may have
taken up germs of disease which formerly
habited the
human body,
causing sickness
and perhaps death, and which might give
rise to like dire results
should they again
secure access to man.
What,
then, shall
be done with the fouled water that has
been collected
?
two answers
Either
:
In general, there are but
it must (1) be turned
body of water so large as to'dilute
beyond all possibility of offence, and
where it cannot endanger human life by
into a
it
polluting a public water supply, or (2)
must
in
some manner be
This fouled water
conduits which
sewerage system
is
it
purified.
called sewage; the
it constitute the
collect
;
and the means adopted
is termed
The terms sewerage and
to get rid of the collected matter
sewage disposal.
sewage, it may be noted here, are often
confounded, even among engineers. The
use of sewerage to indicate the matter carby a sewer, is obsolete, so that one
ried
as properly write or speak of
water- works as of purifying
might about
purifying
sewerage.
To go a
it
may
little further with definitions,
be stated that conduits which cany
water collected from street surfaces, during and after rains, or ground water collected
from beneath the
are called drains.
surface, or both,
Where one
set of con-
removes sewage and another carries
surface and ground water, it is said that
duits
the separate system of sewerage is in use,
a term which may be applied where the
drainage system has not yet been constructed, but only sanitary sewers, as they
often called, have been provided.
set of conduits conveys both
and
drainage water, it is called the
sewage
are
Where one
combined system of sewerage.
Obviously,
various modifications of those two systems
are possible, both for whole cities and for
limited areas within one municipality.
To make the distinction between sewers
and drains more complete, it may be said
s
that sewers carry water fouled with organic wastes from the human system, from
various cleansing
processes
common
to
households, and also manufacturing
wastes; while drains convey rain or ground
all
water only.
The
drainage, however,
may
much
organic matter gathered by
the rain in passing over roofs, yards and
streets, or by the ground water as it percontain
through polluted soil; but this
matter, in most cases, is far less likely to
give offense or menace health than that
colates
contained in sewage.
Before entering into
a
discussion
of
sewerage systems it will be well to consider briefly why they are needed, for the
engineer and the sanitarian must for many
years to come meet the objections to this
class of improvements put forth by men
either ignorant of the principles involved
or,
is
worse yet> of those whose first impulse
to strenuously resist any new demand
upon the public treasury, without regard
to its character.
Public water supplies and sewerage
systems naturally go hand in hand. Where
neither exists water
from
wells,
privies
often
and sink
is
generally drawn
close proximity to
drains, and subject to
in
gross pollution from them. Should there
be a case of typhoid fever in a given house
typhoid germs, which always exist in great
numbers in the dejecta of the patient,
might readily find their way into the
and thus into the digestive system of
well,
members of the family, of visitors,
or of neighbors using the well. Thus the
disease is spread from one member of a
other
family to another and from family to
Besides this danger, there is
family.
always the more remote one from the
dreaded cholera, should it visit the country,
and the ever present one of poor health
and consequent greater susceptibility to
all forms of disease.
A sanitary sewerage system cannot be
installed until a public water supply has
been provided. It is needed as soon as
that is accomplished, for while the wells
can then be abandoned the volume of
waste water
is
greatly augmented
Its foulness
water-works system.
by the
is
also
10
greatly
increased through the
introduc-
Without sewers and
with a public water supply cesspools must
tion of water closets.
be employed. With cesspools begins a
continuous and far-reaching pollution of
the soil, much more serious than that
which commonly results from privies
and the surface disposal of slops. The
pores of the ground become clogged
with organic waste; nature's beneficent
process of oxidation is arrested ; putrefaction sets in ; and poisonous gases are gene-
These gases may find their way
through foundations into houses and also
rated.
directly into the outer air, especially during sudden rises in the ground watrr level.
The cellars of houses on small lots may
be made damp by leaching cesspools.
Such wells as still remain in use are also
liable to pollution from cesspools on neighboring premises. Water tight cesspools,
while possible in theory and often demanded by health ordinances, are a luxury
that only a few can afford, owing to the
Even in percost of frequent emptyings.
meable
'soils
the emptying
of
leaching
11
cesspools as often as health and decency
demand will generally cost more than the
increase in taxes due to the construction
and maintenance of a sewerage system.
A village or town without water-works
and sewers is at great disadvantage as
compared with communities having these
conveniences and safeguards. Industries
and population are not so quickly attracted
the municipality is
almost sure to be poorer and its death rate
These statements hold, only in
higher.
lesser degree, where a public water sup-
to it; the health of
ply but no sewerage system has been provided.
The full benefits of water-works
cannot be enjoyed until sewers are put in,
because many people will make the absence of sewers an excuse for the non-use
or limited use of the water supply.
can describe the trials and tribula-
Who
tions
which beset health authorities
in
their efforts to secure the proper disposal
of privy and cesspool matter ? If there is
little
but privy matter to be removed the
not so great, because in this
difficulties are
country such a condition seldom
exists,
12
except in small communities, where the
houses are set in ample lots, with gardens,
and with an abundance of farm land near
by, so that the vault matter
for fertilizing purposes.
is in demand
With denser
populations and larger areas, the emptying
of vaults is a more serious matter, requir-
ing the greatest care to prevent nuisances,
and often, if not generally, entailing expense upon the householder.
Cesspools
are unmitigated nuisances, and however
well built or frequently emptied, the satisfactory disposal of their contents
cally
impossible.
paratively
little
is
practi-
The matter has com-
value as a fertilizer and
is met with
if the land is
even
increasing protests,
located in remote and sparsely settled
dumping upon unoccupied land
towns.
THE VALUE OF A SEWERAGE SYSTEM.
To express the value of a good sewerage
system in lives or dollars saved is simply
Other sanitary improvements
impossible.
precede, accompany and follow this, each
13
adding to the healthfullness of the community. The decrease in the death rate
for a term of years can be given, but no
man can express in percentages the part
played by each factor. We know that
pure air, pure water, and a pure soil are
essential
good health and long
to
life.
the greatest polluters of air and
and by all odds the greatest enemy to
Among
soil,
pure water,
is
the contaminating matter
from privies, cesspools and improper systems of sewerage and sewage disposal.
These are such truisms that to expand
upon them in these days of progress seems
almost absurd.
Only one
be attempted.
a year are caused
by typhoid fever in the United States.
Keep from the lips of our people all water
illustration will
More than 35,000 deaths
containing germs from the excreta of typhoid patients, and milk diluted with
such water, or contaminated with it
through washing milk cans and bottles
it, and the disease would soon be prac-
in
tically
wiped
out.
This can be effected
only by providing every one with a pure
14
water supply, which, with other much desired ends, would be greatly advanced
by
the provision of properly designed sewer-
age and sewage disposal systems
town and country.*
for both
GOOD ENGINEERING ADVICE ESSENTIAL.
Simple and convincing as the arguments
for efficient sewerage systems seem, years
of agitation are often necessary to awaken
sufficient interest in the subject to secure
their introduction.
One cause
of this
is
the failure to present to the people a wellconsidered scheme, capable of beingunderstood in
citizen
its
and
broad outlines by the average
in all but its most technical
details by any live business or professional
man. How rarely this is done until years
have been spent in well nigh useless effort,
money as well as time often being wasted
*
For the salutary effect upon the general health of
individuals, and especially of women, conferred by the
abolition of outside privies, more or less exposed to the
public view, cold in winter, insufferably hot and odorous
in summtr, impossible of access without getting wet dur" How to Drain a
ing rains or snows, see Waring's
House," Second Edition. This book discusses other benefits to health and otherwise, conferred by a proper system
of disposal for household wastes of the kind under discussion
here.
15
way. Good engineering advice is
needed from the very start in this or any
Otherwise a chaotic
similar enterprise.
in this
mass of opinions as to what should be
done speedily develops, factions spring up
and even political parties take sides on the
questions involved.
PRELIMINARY REPORTS AND PLANS.
Such preliminary studies as are required
need not be very expensive, but they are
essential to a proper understanding of the
Among the data which should be
subject.
determined as early as possible are: (1)
The area to be served, with its topography
and the general character of the soil. (2)
Whether the separate or combined system
of sewerage,
or a compromise
between
to be adopted.
(3) Whether
subsoil drainage shall be attempted.
(4)
these two,
The
is
best of the available
means
of final
the sewage, often the most
disposal
difficult of the problems involved where
of
purification
is
necessary.
(5)
Population,
water consumption and volume of sewage
for which provision must be made, together
16
with rainfall data, if surface drainage is to
be installed. (6) Extent and cost of the
proposed system.
(7)
Method
of meeting
the cost of the sewerage system. (8) The
needs for sewerage peculiar to the locality,
with a study of the health and mortality
of the town.
These are the main points involved in
sewering and draining a town. It may
serve either as a mere outline, or the details suggested by the various heads
may
be so worked out as to form a complete
design for the system.
There is nothing like public confidence,
and the quickest way to unsettle a community and to delay the introduction of
public improvements,
is
to lay before the
A
people a number of conflicting plans.
well-considered preliminary study is likely
to at once
commend
taxpayers, and
if
itself to citizens and
months or even years go
by without further action it continues to
be a rock upon which to build in the future.
Succeeding engineers can but
what has been
commend
so well put in the past, if
they be possessed of sense and ability, and
17
the popular conception of
done
what should be
strengthened with each endorsement of previous recommendations.
The above being true, great care should
is
be taken on the part of local authorities to
the right man for the preliminary
and the fortunate engineer should
exercise even greater care in fulfilling the
select
studies,
trust confided
in
good regarding
him.
final
The same holds
plans
and actual
construction.
Generally speaking, the smaller the com-
munity or the amount of money
available,
the greater the need for the best obtainable advice, although of course the less
intricate the
tion,
problem the cheaper its solueven by the most talented expert. It
only a false economy that dispenses
with engineering services, or employs the
cheapest, because money is to be had only
in small quantities.
Experience is an ex-
is
pensive teacher, and the community that
realizes this at the start will pay the engi-
neer and secure the benefit of his training
in the school of well-directed experience,
instead of taking a
more expensive course
18
of its own in the school of headstrong,
blundering, haphazard experience, which
municipalities have entered.
now suppose that a village, town,
or city has so far decided in favor of a
sewerage system as to be ready to have
so
many
Let us
We
will also
preliminary studies made.
that
it
has
decided
to
have
these
suppose
studies of a comprehensive character.
authorities hesitate somewhat between
The
em-
ploying a local engineer of good general
standing in his profession, and with some
experience in sewerage construction, and
an engineer of national reputation in this
line of work.
Wishing the best they
half decide to engage the latter, but inquiry develops the fact that his charges
are high,
although none too high con-
sidering
experience and knowledge,
that he must be paid for time spent in
his
travelling, and that a comparatively large
amount of ordinary surveying and simple
compilation of facts and figures must be
made, requiring a number of days from a
principal arid assistants. Both the local
man and the expert are finally engaged,
19
the latter to act principally in an advisory
eapaeity throughout the study.
Referring to the above outline for the
preliminary study, it will be seen that the
local engineer will
the
make
the surveys, collect
information
regarding population,
water consumption and rainfall and other
merely local data upon which the design
This
for a sewerage system will depend.
he will submit to the expert for use in
preparing the report of the latter. It is
not necessary to separate any further the
The evolution
of the two engineers.
of the report and recommendations may
therefore be considered as the work of one
work
engineer from start to finish. Indeed it is
likely to be so to a very large extent in practice, the division of labor generally being
carried far to one extreme or the other:
That
is,
either
the expert
amend and approve the
is
called in to
results of
complete
by an engineer with less experience
than himself, or he employs his own as-
studies
sistants,
local
engineers or otherwise, to
do the bulk of the routine work involved.
20
The various
order
(1)
parts of the study in their
may now be taken up, as follows:
The area to be served, with its topog-
raphy and
the general character
of the
soil.
A contour map of the whole municipality,
showing the location of the several streets,
streams, ponds, or lakes and contour lines
for say each 5 ft. of change in elevation
is essential to the best results and must be
provided sooner or later if a sewerage
system is to be carried out on intelligent
lines.
Such a map will be of service for
other purposes and would be a good invest-
ment for any municipality.
The general character of the
soil
usually be ascertained without much
can
diffi-
by more or less casual observation,
and by inquiring among residents, builders and others who have dug wells and
cellars, or observed the same while being
culty
dug.
The kind
of soil
is
important as
affecting the cost of trenching, and its
natural wetness or drynoss, together with
the ground water level, will be a further
indication of the difficulties likely to be
met in construction, and of the necessity
21
or desirability of providing underdrains
for removing ground water or lowering its
which is further considered below.
(2) Whether the separate or combined
system of sewerage, or a compromise be-
level,
tween these two,
is to be adopted.
Obviously, these points depend almost
wholly upon local conditions, including
financial as well as natural factors.
The
and cost of combined sewers is truly
enormous as compared with those on the
size
separate plan, since the surface drainage
in times of heavy rainfall is many times
as great as the flow of sanitary sewage.
In the older towns and cities
it
is
some-
times the case that drains designed to remove only surface water were constructed long ago, before modern plumbing methods were introduced. Such drains
were loosely built, may have been poor in
grade from the start and were never designed to receive sewage.
To-day, how-
ever, they are serving as sewers
ing much trouble and offense
and givthrough
Besides this,
stoppages and stagnation.
they are polluting the soil by means of
numerous
leaks.
In designing a comprehensive sewerage system for such a city, it
sometimes happens that these old drains
can be relegated to their original purposes
and sanitary sewers introduced to care for
house wastes alone.
Where a town or
city
is
entirely or prac-
tically without either sewers or drains,
it
often happens that it may consider itself
fortunate if it can put in sanitary sewers
on the strictly separate plan, leaving surface drainage for future generations, it
may be. Here financial limitations govern,
and this has been the experience of many
American municipalities now possessed
of first-class sanitary sewers.
Many a town is so situated that street
gutters
and natural water courses alone
make ample
provision for surface drainage.
may be insuffithrough various causes, and storm
drains thus be necessary, but there may be
Again, the street gutters
cient,
numerous natural
outlets for these at fre-
quent intervals, thus requiring only short
lines and thus comparatively small storm
drains.
At the same time the only suita-
23
sewage may be at a point
remote from the city, thus necessitating a
ble outlet for
and costly outlet sewer, if the
combined system were to be employed, as
against a comparatively small and inex-
long, large
pensive outlet for sewage alone.
But strongest of all is the case for the
when
the sewage must be
purified.
simply out of the question
for any city to build works large enough
to treat the full flow of a combined system
separate system
It is
at times of
maximum
the sewage
treated, or
must pass away entirely un-
rainfall.
Some
of
very inadequately purified.
Generally speaking, each added drop of
water is so much more burden, for while it
is
true that the sewage is thereby diluted,
also true that the capacity of the works
it is
is
taxed so
much
the more.
If crops are being raised, or even simple
intermittent filtration is in vogue, periods
of heavy rainfall are just the times
a smaller rather than a larger
when
volume of
sewage ig desired, while at chemical precipitation works heavy increases in the sewage
flow are always unwelcome.
The volume
to be treated
in
sewage
is
one of the greatest factors
and the original
and largely its cost, vary
purification,
size of .a plant,
directly with
the volume, while cost of
more largely dependent
volume
than
upon
strength of sewage.
The essential point is, that the combined
system means great extremes and sudden
fluctuations of flow, and whatever the
is
operation
far
character of the industry such conditions
are consistent neither with economy nor
the best results.
Sometimes more or
less limited areas of
a town
may require the combined system
through lack of facilities for near-by disposal of surface water, and again roof
water alone may need to be taken into the
sewers.
and
As
stated above, local conditions
relative costs are the
tors in deciding
governing facbetween the separate and
combined systems.
An
old fallacy concerning the combined
system
may
be mentioned, although
it
has
now
well nigh disappeared: It is that the
storm water will flush the sewers. Regard-
ing this
it
must be remembered that the
25
sewage flow is continuous and likewise the
dangers of and from stoppages, while rainare uncertain in frequency and
falls
amount. As a matter of fact special pains
now taken by the best engineers to give
combined sewers such a section that the
are
dry weather flow will be in a small channel as much as possible like that which
might be employed for sanitary sewers.*
Whether subsoil drainage shall be
(3)
attempted.
As for providing underdrains for remov-
ing ground water, this will also in most
cases depend upon local conditions.
It is
always an advantage to lower the ground
water level in places where
to render the
it is high enough
ground wet at or near the sur-
face through a large part of the year. As
sewers are generally placed below the level
of cellar bottoms and underdrains are most
commonly put below or
at least not higher
than the sewers, it follows that when of
ample size underdrains will lower the
loiv i-;
i-xtended discussions 01' the combined and separate
may be found in Waring s "Sewerage and L :nd
Dra.nage," Staley & Pierson's " Separate System of Sewerage," and the many reports of engineers on proposed sewerage systems.
systems
ground water level to a considerable depth
below the surface and render house foundations practically dry.
It
may
be neces-
sary to supplement the street underdrains
by branches running to the houses, and
even extending through large
lots.
The advantage
beneath and
of rendering dry the soil
around habitations need nut
be enlarged upon here, as it is so generally
well known. But it may not be known to
all
that underdrains are often such great
good sewer construction as to war-
aids to
rant
their introduction
for the
benefits
caused during construction alone. This is
the case where the trenches are so wet as
to render the
making and setting of cement
joints difficult.
By
putting in underdrains
advance of the sewer proper the trench
may be kept dry and the work greatly
facilitated, even where temporary pumps
must be provided to remove the water coliii
lected.
Where
it is
desirable for
any reason to
keep down the sewage flow to the lowest
possible point, underdraius are also of
value without regard to sanitary condi-
27
This
tions.
may
be the case where the
to be purified, or
simply to be
sewage
or
where
several
municipalities
pumped,
is
use a joint outlet sewer, each contributing
towards the maintenance of the outlet in
proportion to the amount of sewage from
The latter condiits individual system.
tions are found in a joint outlet in New
Jersey, where Orange, Bloomfield and
Montclair use the same trunk sewer to
the Passaic River, and have as the only
basis of dividing the cost of maintenance
amount of sewage contributed by each.
Of course the aim in good sewer work is
the
ground water
engineers and contractors know that in very wet soils tight
joints can be made only with difficulty and
to reduce the infiltration of
to a
minimum, but
all
practically never with absolute certainty.
of flow in the outlet of the
The volume
sanitary sewers at East Orange, N. J., was
at one time fully half ground water, according to careful estimates, and that was
after the sewerage system
was well
estab-
lished.
It
must be remembered that with the
28
2-ft. lengths of vitrified sewer
pipe now
almost universally used, there are 2,640
These joints are made
joints to the mile.
of cement, and are not for a moment comparable with the joints of molten lead, with
their
subsequent heavy calking, used in
water main construction.
In view of the above it is evident that
underdrains should be used where they
expected to benefit the health of a
may be
community by lowering the ground water
level;
where they
will be sufficient aids to
sewer construction to warrant their introduction for this purpose, to which is also to
be added their permanent benefit; and
finally,
where
it is
desirable to
employ them
to prevent an increase through infiltration
of the volume carried by the sewage, in
which case the benefit to health will also
accrue.
(4) The best of the available means
the final disposal of the sewage.
for
Until recently this part of the problem, at
America, meant only into which of
the near-by streams or lakes or at what
point in tide water could the crude sewage
least in
be discharged at the least cost and with the
minimum of offence. Too often the matter
was given only scant considerand sometimes none at all. Un-
of offence
ation,
fortunately many cities are to-day facing
the problem in the same manner, but the
advance of modern sanitation
more and more imposible.
is
rendering
this
The
cardinal principle in the ultimate
disposal of sewage is that no public water
supply
be
should
Strange to say, this
endangered thereby.
must be interpreted as
meaning that no city should endanger the
water supply of either itself or its neighbors.
This is almost inconceivable, for while one
can imagine a city mean or ignorant enough
to
endanger the
lives of the citizens of
an
adjoining community, it seems incredible
that any municipality should be sufficiently
reckless to poison its water supply with its
own excreta. But both conditions exist and
must be combated.
This deplorable state
be
may
explained in part by the
general ignorance of sanitary matters
which has prevailed until of late, and in
of affairs
fact
is
seen
still
to exist
when one com-
pares what is with what should le. It
does seem, though, that common sense and
common decency combined ought
to be
prevent a city from drinking
sewage or forcing it down the
sufficient to
its
own
throats of others.
Coming back
to the
expressed above 3
constitutes
it
cardinal principle
may
be asked "what
the endangering of a public
water supply?" No very definite answer
can be given at present, owing to our lack
of knowledge regarding the exact length
of time which disease germs from the
human system
will
live
in
water.
The
Massachusetts legislature some time ago
said that no excreta should be discharged
into
a stream within
point where
20 miles of
any
used for a public water
in
the
matter of new water
but
supply,
and sewerage construction it has practiit
is
cally placed the subject in the hands of
There are no
its State Board of Health.
data to-day which will warrant an engineer in saying that disease germs may not
be conveyed more than 20 in les by the
;
waters of a stream and afterwards cause
31
sickness and perhaps death. The engineer
and sanitarian will consider the distance
which must be traversed by the sewage
dilution which it would receive
before reaching a public water supply, to-
and the
gether with the
minimum
length of time
which would elapse before a disease germ
could pass from one human system to
Unless
another, a most important point.
distance, dilution, and time are great, sewage should be purified or carried elsewhere
for disposal.
Of course there may be
cases
where
sewage disposal seems to claim preference
to water supply, in the use of a stream.
Each of these must be adjusted on its own
merits.
The
willful pollution
of public
water supplies, even, if it seems remote,
should no longer be tolerated, and where
new sewerage systems
is
unnecessary that
Given a body of
it
are being
should be.
Avater,
built, it
not used, nor
likely to be employee! for a public water
supply, the case is far different. Knowing
amount of water and the probable
quantity and character of the sewage, it is
the
generally eay to determine whether all
the crude sewage of the city can safely be
discharged into the water in question.
Averages are of no use here. The water
available during a hot dry summer, when
the stream, pond or lake is at its lowest,
and banks and beds are exposed to the
sun, is what must be considered.
Partial purification may be sufficient
through a few months or all of the year
for
some
and works have been carBut most plants
country have been built under concities,
ried out on that basis.
in this
ditions that
demand continuous
operation
at their utmost efficiency.
Where sewage is discharged into large
bodies of water, either lakes or the ocean,
generally necessary to make a careful
study of the prevailing currents in order
it is
most available point or
points of discharge in order to prevent the
sewage becoming stagnant in bays or the
to determine the
washing ashore of its lighter portions.
Such studies are commonly made by floats,
as direction
of current
is
factor of prime importance.
generally the
33
When
it
is
decided that purification
must be employed, it becomes necessary
to select the method best suited to local
needs and conditions. This matter can
better be
discussed after the subject of
purification has been taken up in detail,
further on, and so will be dropped for the
present.
In concluding this phase of the subject,
or postponing its further consideration, it
may be said that until new advances have
been made in the recovery of fertilizing
matter from sewage, no compunction need
be felt in discharging such into any body
of water which can receive it without
harm.
Where such water
is
available
it is
often a mere question of the relative cost
of an outfall to it and a shorter outfall
with purification works to a nearer point
of discharge where purification is necesOf course treatment of the sewage
sary.
is
sometimes the only course which has a
shadow
of practicability.
Again all conof such a procedure is often
sideration
unnecessary by an especially
available point for the discharge of un-
rendered
34
sewage.
purified
Where
there
is
uncer-
best to keep on the safe side and
tainty
Uncerprovide purification at the start.
in
these
matters
means
tainty to-day
it is
certainty in favor of purification to-morwe advancing in sanitation
row, so fast are
and so rapid is the increase of population
and also of the pollution of our streams.
(5)
Population, water consumption,
and
volume of sewage for which provision
should be made, together with rainfall
data if surface drainage
is to be installed-
The
basis for population studies will generally be the United States census for a
number of decades past, with figures for
as
intermediate years as possible
local numerations.
these figures percentages of growth
many
filled in
From
from State and
for decades or shorter intervals
may
be
computed and population curves plotted,
and from one or both of these, coupled
with present local conditions and future
prospects, the
30 to 50 years
population for the next
may be forecast by decades
or half decades.
In small and
rapidly
35
growing communities
it
must be remem-
bered that the percentage of increase
generally
less as the
greater.
It is desirable to
is
population becomes
design a
sewerage
number
system large enough
of years to come, say 30, though parts of
the work need not be made so large, as
to serve for a
pumping or
purification
works where either
or both of these are necessary.
It is rarely the case that the whole population of smaller communities is connected
with the sewers until years have elapsed
after the construction of a system.
This is
due to lack of sewers on some streets and
to that strange perversity of human nature
which leads many people to put off the
making of sewer connections as long
as
possible, notwithstanding the fact that the
soil of their premises is daily becoming
more and more polluted with excrementitious matter, and that the yearly expense
of properly cleaning privies and cesspools
is greater than the interest on the investment necessary for making sewer connec-
3G
tions.
In
some communities allowances
for these delays may be made in designing
pumping or purification works, but the
pipe system should be large enough at the
start to serve each street and district for
an indefinitely long period.
The advan-
tages of the use of city sewers are so great
that all property is bound to be connected
with them sooner or
later, leased property
without these conveniences soon dropping
in market value.
In view of these facts
the population figures are sometimes based
on an estimatad number of people per acre,
or per lineal foot of sewer, more especially
where a separate system of sanitary sewers
being constructed. Safe figures of the
cannot be laid down for general application, but must be decided on
is
latter class
after a careful study of the
question, the character of
community
its
in
residence
property and general population. Often it
is necessary to divide a city into districts
its population and rate of flow studies.
Thus the residence sections occupied by the
for
wealthiest classes will be comprised of a
37
comparatively small population per acre,
duo to the large size of the lots. The
grow more dense
population will
in the
passage through the sections occupied by
the less wealthy, the well-to-do and finally
the tenement sections.
city devoted to
The
portions of a
manufacturing will in some
sewage and manufacturing
cities contribute
wastes in pretty close proportion to the
number of employers, while in others, or
in different lines of
industry, the sewage
yield will vary more especially with the
character of the goods being produced.
The total water consumption is of course
mainly dependent upon the population,
and these two factors together enter largely into the
amount of sewage requiring re-
moval and
disposal.
No
fixed rule can be
down
for water consumption, except
that in general it is on the increase in all
laid
American cities, and in many places has
reached immense and sometimes alarming
proportions. It may be kept down by proper inspection and the use of meters for
the prevention of waste, as it is absolute
38
waste and not beneficial use which
is re-
sponsible for high water consumption.
The instances are rare where it is safe to
less than 60 gallons per capita
as
the average water consumption
per day
of a town, if most of the people patronize
allow for
the public water supply.
were to be
laid
If a general rule
down 100 gallons would be
a safer figure.
Obviously not all the water
which passes through a water- works system
reaches the sewers.
is
for
In
summer much
lawn and
of
it
street sprinkling
employed
and similar purposes, very little of which
reaches the sewers even where the combined system is in use, and practically
none where a separate system of sanitary
sewers is employed. But while all this
tends to diminish the sewage yield the infiltration of ground water, already discussed, increases it, and average daily figures have been discussed above, while
works must be built on the basis of maximum daily, or even hourly, yields. Altogether, then, 100 gallons per capita will be
none too large except in particular cases or
possibly for the immediate present, where
39
a portion of the works can be built for
future enlargement.*
The total daily flow of sewage is not
distributed evenly through the 24 hours.
The actual percentages at different hours
day vary widely, according to the
nature and occupations of the contributory
populations. In most towns there should
of the
be scarcely any sewage,
enough
tween say 10
period of from
tight
if
to prevent
P.
M.
the sewers are
infiltration, be-
and 4 to
6 A. M., a
six to eight hours.
As
a
matter of fact few sewerage systems exist
where the flow during these hours is not
considerable.
From
two-thirds to three-
fourths of the daily flow generally occurs
during from say nine to twelve hours of
the day, the particular hours varying some-
what
in different
communities and having
or no significance in designing the
smaller portions of most pipe systems, but
affecting the outlets and being of great
little
* For an extended
study of vater consumption, with
large number of American municipalities
and with much other data on tlie relation of this subject and of population to amount of sewage, see Rafter
& Baker's "Sewage Disposal in the United States."
figures for a
40
importance where
the sewage
must be
lifted or treated before its final discharge.
Moreover, there are generally from one to
three hours in the day when the flow is
considerably above the average for the
The
heaviest ten hours.
actual
amount
of
sewage for these hours must be taken into
consideration in the separate system and
the plant designed accordingly. For ordinary laterals, these fluctuations need not
be taken into account, for in the best practice these are
for their duty.
generally more than ample
As the sewers increase in
and territory served, and as disposal
works are reached, the flow during maximum hours becomes of more importance.
size
Roughly
speaking,
total daily flow in
10 per cent, of the
may be con-
one hour
sidered a perfectly safe limit.*
When the sewers are being proportioned
for their respective streets and districts,
density of population must be considered.
It is generally necessary to arrive at this
"
*
Staley & Pierson, in the
Separate System of Sewerage," givtt ihu maximum hourly flow as twice the
mean hotirly flow, which would be about 8 3 per cent,
of the total daily flow.
41
an arbitrary way, as actual figures, except for the whole town, are seldom available except in communities long since
sewered, or that may be considered as
in
having reached their full growth. The
proper figures must be reached for each
community separately, so no attempt will
be made to give them here.
Rainfall data are liable to be very scarce
in all but the larger cities and towns, and
at points where the national and state
weather bureaus have stations or observers.
Such defects in the records as exthrough lack of observations, simply,
cannot be remedied, but it sometimes hap-
ist
pens that figures for near-by towns will do
But even when records are
very well.
available they may not be sufficiently detailed for the purposes under discussion.
Monthly or weekly totals are of scarcely
any
use,
and even daily records do not
completely meet the
case.
What
is
necessities
of the
where storm sewers
the duration and rate
desired
are to be provided is
of precipitation of the heaviest rains.
very heavy shower of
15 minutes
A
may
42
cause more inconvenience and damage, if
the sewers are inadequate, than a steady
There
rain extending over a day or two.
of course, a limit to the size of sewers*
imposed by financial, and in some cases by
is,
physical conditions.
Oftentimes, where
sharp, heavy rainfalls occur, their complete
speedy removal is impossible, and the surface water simply must be allowed to
Sewers may generally
stand for awhile.
be so designed that they will speedily re
the total rainfall except at long in
tervals when an unusual precipitation oc^
move
curs.
After a careful study of
all
the rainfall
records available and a consideration of
the slope and character of tha
area, especially
with paved
in forest
drainage
whether closely built up,
streets,
many
roofs, small areas
and under cultivation, or
the
the rate of rainfall per hour
furnish the basis of calculashall
which
contrary,
tions
may
readily be decided upon by any
A maximum rate of
competent engineer.
1 in. per hour may be considered as a
liberal figure in
some
localities.
The
pro-
43
portion of this which will reach the sewers
during a given time will depend upon such
factors
local
surface
its
slope of land,
as
whether
covered with houses and
is
paved streets, cultivated fields, or forests,
and the permeability of such soil as is
exposed.
Extent and cost of the proposed
(6)
system.
This
is
a
matter
largely
dependent
local treasury, or the willingness of the people to incur indebtedness,
upon the
levy general taxes, or pay special assessments for benefits, as the case may be.
The
to afford every buildcommunity an opportunity to
ideal plan
ing in the
is
connect with the sewerage system. This
cannot often be done at the start, and in
most instances sparsely settled outlying
districts must wait long and weary years
before the sewers reach
them, although
their taxpayers may be called upon year
after year to pay taxes to redeem i,he
bonds, meet interest, maintenance and repairs.
The
and most thickly settled
community naturally will
oldest
portions of the
44
be sewered first, after which the system
should be carried as far out in various
Directions as the funds available will perThe exact course followed will de-
mit.
pend largely upon the legislative authority
conferred upon a given municipality to
raise money for sewerage construction.
Practice in the several States, and often in
the various cities and towns of one State,
Somevaries widely in these particulars.
times the city authorities have full power
to lay out as complete a system as they
deem best, either issuing bonds for its construction or levying assessments for benefits upon abutting property owners for a
part or the whole of the work. Again,
there is authority only for the construction
of trunk sewers and other works for final
disposal, the building of laterals depending entirely upon the initiative of property
owners.
All the local conditions, legal
and otherwise, must be ascertained before
the extent of the system can be settled.
All work should be planned and carried
out with the future in view and should be
complete and adequate
in itself
and
in re-
45
lation to other parts of the system, so that
reconstruction will not be necessary for
years to come,
if
ever.
appears from the above, and from a
simple common-sense view of the subject
without regard to what has been written,
It
the system will be
governed very largely by the local pocketbook and existing statutes, and that it
that
the extent of
should be
made
to suit the
most pressing
needs of the community and be capable of
easy extension as soon as possible.
The
cost of the system will be a matter
for estimate in each case.
Most sewer work,
especially for sanitary sewers, is so simple,
and there is now so much of it being esti-
mated upon and carried out by engineers
and contractors, that it is comparatively
easy to figure up the approximate cost of
a sewerage system. Local prices of labor
and freight rates on sewer pipe, cement and
brick, where the latter is used, are the
main factors, and must be decided upon
by each engineer in making up his cost
The technical papers now pubestimates.
lish
exhaustive detailed
lists
of bids for
46
sewer work
all over the country, and
the reports of city engineers, superintendents of sewers, sewerage committees and
boards of public works often abound in
work
figures or quantities and cost of
actually done.
(7)
Method of meeting
system.
As stated
down by
this
above,
so
law,
that
the
is
cost
laid
often
there
is
the
of
little
choice to be had, except in the details.
But ample
latitude
is
sometimes
left
and
generally the details of carrying out even
fairly definite laws afford a chance for a
considerable
amount
of variation, together
with much study.
Broadly speaking there are two methods
of raising
money
sewerage system
a charge upon
raising the
isssue;
and
:
to defray the cost of a
(1) By making the work
the
whole municipality,
taxation or a bond
money by
(2) assessing the cost
upon the
A
combinaproperty specially benefited.
The
tion of these plans is very common.
first
one
is
sometimes put into
effect
and
the second with comparative infrequency,
47
except for single streets or drainage districts of a city with independent outlets.
The trouble with
the second plan is that it
not easy to determine the proportionate
amount of benefit which each property
is
owner
receives, unless
it
be in the most
simple cises.
The cost of constructing and operating
a water- works system is met by the yearly
rentals charged for water furnished the
users of the same, but the general aim in
the case of sewers is to make their use as
popular as possible.
Therefore, the most
common
practice in this country has been
to charge nothing for using the sewer. An
entrance fee, sometimes designed to repay
the city the cost of supervising the work,
and sometimes intended to help pay for or
maintain the system, is often charged for
connecting with the sewers and paid once
for
all.
The
actual cost of house connections
is
always, so far as the writer knows, borne
by the house owner.
Where
the general public and the property especially benefited, that is, actually
48
or potentially served by the system as conshare the cost, it is divided in
various proportions, seemingly without
structed,
rhyme
may
many instances. It
may be the property
all
the way from one
pays
or reason, in
be the city or
benefited that
to three-fourths
it
of the cost,
or perhaps
through a wider range. With the separate
system of sanitary sewers a popular plan
and an apparently
cost
is
simply
to
fair
be
one,
where the
divided as stated
above, is to assess upon abutting
property the cost of the smallest-sized
lateral sewer, or in other words of a
just
sewer just large enough to serve the
houses on one street of moderate length.
The
further cost
tensions,
system or exbe raised in the
of the
would then
general tax levy or by a sale of bonds.
The assessments for benefits are levied
upon the frontage bordering on the streets
in which the sewers are laid, or upon the
area of th'e lots, or are divided between
these methods. The whole subject under
discussion is a complicated one and has
49
never received the consideration
it
deserves
from municipal
But to one such an
officers.*
official, great credit
should be given for having made a very
exhaustive investigation of the problem
and presented a solution which aims to be
conducive to the rapid extension and
use of his particular sewerage system, and
in many points admirably adapted to other
fair,
localities.
This study was
made by Mr.
F. H. Snow, City Engineer of Brockton,
Mass., and the plan recommended was
A
adopted by that city.
summary of Mr.
Snow's report is given below, the importance of the subject, the lack of both popular and technical information regarding it,
and the value of the report itself, seeming
to warrant the devotion of a few pages to
this purpose. f
The population of Brockton is about
The sewerage system includes a
30,000.
* A
monograph, entitled "Special Assessments," by
Victor Kosewater. (Columbia College Studies in History,
Economics and Public Law) will be of interest and value
to those who wish to pursue the general subject further.
t This summary is condensed from an editorial digest
and discussion by the writer which appeared in " Engineering iVeutt" of Ju y 19, 1894.
50
receiving reservoir, pumping station, force
main and filter beds. The first cost of the
system, so far as constructed, was raised
by an issue of bonds. The summary is as
follows
:
In arriving at the proper plan for Brockton, Mr.
studied with great care the various methods
Snow
of assessments already in use, after first having
shown that the benefits of a sewerage system were
partly public and partly private, and should be
borne accordingly. Public benefits are, of course,
to be met by general taxation.
The proportion to
be paid by the public has been fixed by the Massachusetts legislature at not less than one-fourth nor
more than two-thirds of the total cost of the sewer-
For private benefits a variety of
methods are permitted by the statutes, such as
frontage and area assessments, yearly rentals,
age system.
******
entrance fees, or a combination of these.
Either the frontage or the area plan alone is
shown by Mr. Snow to be inequitable, diagrams
being used to illustrate how by either plan differences in the shape of lots may allow several houses
on one
lot and only one or two on another, each
having the same area or frontage, as the case
may be. The entrance fee is also shown to be
unjust, unless it is graded in accordance with bene-
lot
fits
received, while, in addition, a large fee
would
51
be required
at the start,
when
there were but few
connections, or else reliance on the general tax
levy would be necessary
The method
finally
.
recommended by Mr. Snow
given in his report as follows
It is recommended that one-fourth of the total
cost of the sewerage system be raised by first
assessment, one-half by rental, and the remainder
is
:
by general
tax.
It is also
recommended
that first
assessmant be based on area and frontage of land
adjacent to sewers 0.6 on area within 125 ft. of
4 on frontage that the first
the street line and
assessment be collected in one payment and
credited to construction account that the unit of
rental be 1,000 gallons of water reaching the
sewer, this to be ascertained from meter gagings
of the water department, and to be corrected for
water finding another outlet than the sewer by a
system of discounts 70 per cent, to be deducted
from water supply of shops and 20 per cent, from
water supply of houses having sill-cocks.
And it is further recommended that abuttors be
not compelled to enter the sewer as soon as completed that no one be allowed to enter without a
permit that no rent be charged users before January 1, 189.5, rents starting from that date that
such rents be charged from the first of the month
following that in which the permit is dated and
that all deficiencies be made up in the early years
by general tax levy.
It is further recommended that the following
For first assessment,
prices be assessed per unit
0.3 cents per square foot, and 15 cents per front
foot; for rental, 28 cents per 1,000 gallons entering the sewer and that $8.40 be charged for unmetered connections, subject to a discount of 20
;
;
;
;
;
;
;
:
;
per cent, for sill-cocks.
These first assessments represent the value of
the sewerage system to land, in enhancing its price
without regard to whether the sewers are used by
the owners of the land. The amount raised by
general taxation will likewise represent the benefit
to the community as a whole, without regard to
the locat'on of the sewers.
Benefits from actual
use of the sewers are to be paid by rental, acsording to the amount of sewage contributed, and the
sums so raised
will be applied to paying off the
bonds, meeting interest and to maintenance. The
rentals will pay two-thirds of the total yearly
charges, leaving the balance to be
taxation.
met by general
It is eminently fitting that rental should be
based on the amount of sewage contributed, since
upon the
latter
depends the
size of the sewers,
and
notably the cost of constructing and operating the
pumping plant and filter beds.
Fortunately at
Brockton G5 per cent, rf the water connections
are metered and the records of the water department are well kept, so that the sewer rentals can
Obvieasily be based on the water consumption.
ously on many premises some of the water used
does not find its way to the sewers, hence the proposed deduction of 20 per cent, of the consumpand of
tion for houses having sill-cocks for hose
70 per cent for shops.
53
The unit of 28 cts. per 1,000 gallons of water
was arrived at by computing the probable yearly
expenses of the sewerage system until 1900 and the
probable water comsumption for the same period.
It should be stated that the water consumption in
Brockton is phenomenally low, only 25 gallons p( r
The yearly rate of $8.40 for unmetered
capita.
houses was chosen because the minimum rates for
metered water are such as to make it an object to
when the water consumption goes above a point that would call for
water users to have a meter
such a rental.
Coming to the amount to be raised yearly in the
tax levy, the problem is simple, the amount being
the difference between the total amount to be
and that provided for as outlined above.
Although this system has been worked out to
meet the situation of Brockton, which is in a numraised
ber of respects unique, the general principles
involved may be applicable in other places. The
special conditions at Brockton are as follows; (1)
No sewers are yet in use, although the city has a
population of about 30,000; this renders possible
the adoption of any desirable system without the
unfairness, real or fancied, which follows a change
in the case of old systems.
(2) It is expected that
the whole city will be sewered in a comparatively
few years, so that the total cost of the system can
be readily estimated, which
plan.
(3)
The
is
essential to this
large percentage of metered water
54
taps and the fact that the city
owns the water-
works, so that water and sewer departments can
co-operate, while each desires to keep the water
consumption down, are favorable to a yearly
Modirental plan, based on water consumption.
fications of these conditions might make the
system
tion
difficult
when
of application or might cause fricNevertheless- the principles at
applied.
the bottom of it
seem correct, and this general
distribution of the burden of a sewerage system,
whether in these or other proportions, seems fair
and likely to be popular. General public and
individual private benefit are each recognized and
the latter is divided into two classes, (1) potential
benefit through increased value of a certain piece
of property because the sewer passes by it and may
be used, and (2) the actual benefit through use.
Two dangers which beset the extremes of the
two methods most usually employed to raise
money for sewers seem likely to be counteracted
to a large extent by this plan:
(l) When the
whole cost is put in the general tax levy or is met by
bonds, the interest and principal of which must be
met by taxes, it is difficult to secure money for extentensions, every taxpayer wishing to keep the rate
down, and those living on sewered streets having
no
direct interest in extensions.
In the Brockton
plan the t~x levy is increased by only one-fourth
the total cost of the sewers, the bulk of the expenditure being put upon those whose land
is
55
improved or those who, by use of the sewers, are
saved the expense of cleaning cesspools or privy
vaults.
system
The taxpayer
is,
to
feels
that
the
sewerage
large extent, self-sustaining, like a
(2) The other
municipal water-works plant.
danger is that where property benefited bears the
whole expense of sewers it will, in case of assess-
ments for frontage or area, try to keep the sewer
out of the street. But in Brockton a given property owner will be paying towards one-fourth the
whether the sewers are in his
and once in his street he need pay
cost of the system
street or not,
only an additional one-fourth for property benefit,
unless he wishes to connect with the sewer.
The
sewer once in, however, he will already be paying
towards one-half of the total cost of the system and
the additional expense for the use of the sewer will
small.
Moreover, by economy in the use of
seem
rental may be kept low, and most
people do not consider themselves extravagant
water users.
water his
(8)
The
needs of sewerage peculiar to
of the health and
the locality^ with a study
mortality, of the town.
Little
need be said on these phases of
the subject. The adoption of a scheme
and the raising of money for its realization
may
be greatly aided by showing that
demand the
local conditions imperatively
-56
A
study of the health and
mortality of the town, and comparisons of
the results with like studies of communi-
improvement.
ties
enjoying good sewerage systems
is
often helpful in enlisting popular enthusiasm for sanitary progress.
But such
work must be done wisely and
false state-
ments and impressions regarding the relation between unsanitary conditions and
disease avoided as one would shun poison.
There has been so much ranting of late regarding deadly disease germs lurking here,
there and everywhere that many persons
on reflecting that they and most of their
neighbors
still
live,
grow
suspicious
feel inclined to discredit the
and
germ theory
of disease and the advantage of cleanliness
in all the departments of life.
It must be
remembered that
just as
there are thou-
sands of visible forms of plant life, of
which only a very small percentage are
poisonous, so
among
the
many
invisible
forms of plant life known as bacteria or
microbes there are only a few harmful
germs. These few, it must be taught,
,
give
rise
to
dire
results
when allowed
57
access to private water supplies, like house-
through leaching privies and cesspools, or to public water supplies by discharging crude sewage into streams or
lakes from which such supplies are drawn.
Furthermore, unsanitary conditions, while
not giving rise to certain forms of disease,
wells,
may render the human system unfit to ward
off attacks of the same.
reasonably presented,
Facts like these,
a
may sometimes do
world of good in an engineer's report,
while the too common exaggerations would
disarm instead of assure the people.
ADOPTION OF THE ENGINEER'S REPORT.
The
report of the engineer having been
completed and submitted to the proper
officials its
assumed.
adoption by them them
may
be
Sometimes the
plan recommended has to be submitted to a popular
vote, but more often where a vote is taken
it is
only indirectly upon the specific plans
proposed, the real question being whether
bonds shall or shall not be issued for the
execution of the scheme.
ral report is
After the gene-
adopted the next step
is
to
58
select
an engineer to
prepare
detailed
and
specifications preparatory to
contractors.
advertising for bids from
plans
Frequently the engineer
who made
the
engaged as designing engineer and sometimes to supervise
preliminary studies
is
construction as well.
This
course
has
the advantage of continuing the services
of one more or less familiar with local
conditions,
and with the plan for seweralready partially worked
ing the town
out.
DESIGN AND CONSTRUCTION OF THE CONDUIT SYSTEM.
The
first
work
of the engineer will be
to design his pipe or conduit system. For
this task the topographical map already
mentioned will be a help, but this should
be supplemented by a profiles of all the
streets in which sewers are to be laid, in
order that the proper grades may be deter-
mined and the
accessories of the systems
designed.
Numerous diagrams and
tables are avail-
able for use in designing conduit systems,
59
rendering separate computations with the
aid of complicated formulae altogether unnecessary, unless the engineer wishes to
his own figures.* In the separate sys-
make
tem
it is
the
minimum
generally best to use 8-in. pipe as
size, in order to lessen the
risk of stoppages,
for the
although 6 ins. is ample
volume of sanitary sewage from an
ordinary residence street of medium length.
Pipe sewers are generally made of vitrified
clay,
with
a
salt-glazed
surface.
Cement pipe (cement and sand) is also
used 'in some cities. The size* of pipe
sewer was for many years limited to a
diameter of 24 ins. but some of the manufacturers now make pipe 36 ins. in diamThe 24 in. limit was
eter for general use.
in force because of the difficulty and expense of making the larger pipe and the
comparative ease of laying brick sewers of
any size from 24 ins. up. Monolithic sewers
* Mathematical dipcussions of sewer formulae are beyond
the bcope of this work. See Baumeister's "Cleaning and
"
Sewerage of Cities for a brief but able presentation of the
subject, illustrated by diagrams, and Flynn's "Flow of
Water in Open Channels, Pipers Sewers, Conduits, etc.," for
"
tables. Staley & Piersou's
Separate Systems of Sewerage
"
may also be "consulted. More recent books are Ogden's
Sewer Design and FolwelTs Sewerage."
' '
60
have been used for a limited extent, the
conduits being built in place from cement
mortar.* In very wet ground cast iron
pipe with lead joints is used, either because
it
is
specially desirable to prevent
because of fear of damage
infiltration or
through settlements.
The pipe should be laid to grade with
great care, and a good alignment should
be secured. Holes should be dug for the
bells of the pipe so that each length of
the latter will have a solid bearing throughout.
When the material is such
as to
make
uncertain a solid support for the pipe, sand,
gravel, concrete, plank or piles should be
employed for the purpose.
countered in trenching,
If rock
is
en-
will Le necessary
for the pipe which will
it
to provide a bed
not be washed into fissures
of sub-soil water
the eewer
which
is
when the ground
Little Falls,
N.
by the stream
likely to follow
is saturated. At
Y., in the case of a vitri-
a water supply conduit,
such a washing-out of material occurred,
fied pipe line for
*
Concrete, both plain and reinlomd vith steel, has bt-en
into n*e since the lit t ed.tion c f this book was \N rit(it>U5;, but u.ore puniculaily for large fcew<,is.
coming
uu
61
causing settlements and the pulling apart
of joints. The trench was opened through
the rock portion and the pipe
embedded
in
concrete.
SUBSOIL DRAINS, OR UNDERDRAINS.
Where
sewers are in wet sand or gravel,
subsoil drains, or, as they are more usually
called, underdrains may be laid beneath or
alongside the sewer to advantage, as discussed above. These are generally simple
from
have
agricultural tiles
3 ins. in diameter
no joints, being
They
upward.
hollow
cylinders, and are laid with
simply
their ends a fraction of an inch apart,
wrapped with a cheap so-called muslin
cloth, or
other suitable material to keep
out the dirt until the matter in the trench
becomes thoroughly packed about them.
These underdrains may almost always be
emptied into the nearest stream, provided
it is not used as a public water supply.
This qualification is on account of the fact
that the sewers may leak and sewage thus
Such
was con-
flow directly into the underdrains.
danger
may seem
remote, but
it
62
sidered sufficient to cause the city of Boston to refuse to pay a promised sum toward
the cost of
the"
sewers of South Framing-
ham, Mass., so long as the sewer underdrainge discharged into a stream tributary
to one of the sources of the Boston water
supply. Boston had agreed to make this
contribution in order to induce the town
of Framingham to remove
from the Boston water works.
purification necessary, which
manded
pumped
-its
sewage
This
made
de-
in turn
that all the sewage should be
to the- filter beds and irrigation
Naturally the town did not wish
pump and purify the underdrainage, but
area.
to
some years of delay and an offer of
an additional sum from the city of Boston
the town constructed reservoirs and filter
beds for the purification of the underdrainage, all of which must be pumped a small
after
lift.
Perhaps one of the best examples of
subsoil drains beneath sanitary sewers, or
at least the best example which has been
described and illustrated in detail,
is
at
63
Newton, Mass., where drains were placed
below many miles of sewers.*
MANHOLES.
Manholes should be placed at all changes
of grade and at all junctions between two
or more street sewers. These are built of
brick and afford access to the sewer for
In addition they are someinspection.
times used for flushing.
They
are
pro-
vided with iron covers, the latter often
being pierced with holes to afford ventilation to the sewers.
When
the covers are
perforated pails are often suspended
beneath to catch the dirt from the street
so
surface, especially
in
when
the manholes are
macadamized gravel or
dirt streets.
On
long stretches of straight sewers
lampholes are somtimes put in between
manholes, consisting generally of a vertical
piece of pipe extending from the sewer
nearly to the surface and provided with a
cover.
These are valuable aids to inspection.
*
See Engineering News, January
description of this system.
2,
1896, for illustrated
64
SEWER GRADES.
The grades
where
of sewers should be sufficent,
possible, to give
them a
self-cleans-
ing velocity, thus rendering stoppages from
ordinary suspended matters impossible.
"
Baumeister, in his
Cleaning and Sewerage of Cities," makes the following state-
ments on
this subject:
Practical experiments show that sewers of the
usual sections will remain clean with the follow-
ing
minimum
2
tions,
separate house conneccases, 1 per cent.
grades:
per cent.
extreme
;
Small street sewers,
1
per cent.
;
extreme cases,
Main sewers, 0.7 per cent. ex0.7 percent.
treme cases, 0.5 per cent. The extreme cases are
;
for sewers carrying only rain or quite pure water.
The following empirical formula will give the
minimum
grade for a sewer of clear diameter
equal to d inches and either circular or oval in
section
:
Minimum
grade, in per cent
~r
100
>_i_ro
FLUSHING DEVICES.
Where very low
and
grades are unavoidable
branch sewers where
at the heads of
the volume of flow
is
small, flushing may
In some cases a
be used with advantage.
65
copious supply of water is turned into the
sewer through a manhole from some
stream, pond or lake, or from the public
water works system. Generally, however,
the water introduced is allowed to accumulate before discharge, being held back,
for instance, by plugging up the lower
side of a
lates in
manhole
it,
until the
water accumu-
then suddenly withdrawing the
plug and releasing the water, upon which
rushes down the sewer carrying before
practically all
treme
it
it
obstructions, except in ex-
cases.
Instead of relying upon clear water, as
described above, it may l,e sufficient at
some points on the system to simply back
up the sewage by plugging the manhole
outlet, thus
sewage
flushing the
sewer with the
itself.
The necessity of frequent and regular
flushing has given rise to automatic flushing tanks. These generally make use of
the siphon for self-discharge, although
there
is
on the market a purely gravity
flush
tank,
when
full.
which
tips by its own weight
Whatever the means of dis-
charge the feed to the tank is regulated by
a valve or cock on the supply pipe, so the
tank will fill and empty once in a given
number
of hours.
Y-BKANCHES FOR HOUSE CONNECTIONS.
Provision for house connections should
be made when laying sewers,
avoid as
much
as
may
in order to
be tearing up the
streets after the pipe system is in
breaking of holes into the sewer.
and the
It is a
wise plan to lay the house connections
from the street sewer to the curb, or even
across the sidewalk, while the street is dug
At the least Y-branches for house
up.
connections should be put in at frequent
intervals, say from 25 ft. apart upwards,
according to the character of the street.
When the sewer is put down deep quarter
bends are sometimes provided and the
house connection pipe carried vertically
upwards
until within a
few
face to avoid deep digging.
house connection may join
feet of the sur-
However
the
the sewer, or
any two sewers join each other, the direction of flow in connection and street sewer
67
should be as nearly the same as possible,
and the entering sewer should be at a little
higher level than the sewer entered in
order to increase the velocity of the influent sewage and thus lessen the tendency
retardation and stoppage which naturally results where two confined streams
to
with matters in suspension unite.
DEPTH OF SEWERS BELOW SURFACE OF
GROUND.
No
general rule can be laid down for the
depth of sewers further than that they
must be deep enough
to :idmit
of house
connections with a proper fall, and on the
other hand should be p.s near the surface
as possible
to
save the expense of deep
trenching. Of course they must be kept
below the point at which clanger from
freezing
might
arise,
but
the
natural
usually sufficient to make such a
consideration unnecessary, especially as the
depth
is
temperature of sewage is generally a number of degrees above that of the atmosphere at the street surface.
68
VENTILATION OF SEWEKS.
The
ventilation
of sewers
is
a subject
fraught with many fears and perIn the early days of sewers the
plexities.
still
conduits were faulty in the design of their
cross-sections, in their grades
construction.
and
all of
in their
these con-
Practically
duits originally carried surface water,
and
large quantities of
Many of these conduits,
infiltration
through
ground water.
as stated at the beginning, were built to
carry storm water alone, in other words
were simply drains. With the advent of
ample public water supplies and modern
plumbing, which, with its many fixtures
providing hot and cold water at every
hand led to high water consumption,
houses were connected with the drains,
Still
thus converting them into sewers.
this
the
of
convenience
later,
practice being
recognized, conduits were designed and
built to carry both drainage and sewage,
but these sewers on what we now call the
combined system were little or no better
in design and construction than the old
69
drains.
The consequence of all
was that the uneven bottoms made
surface
this
long stretches of sewer little or no better
than cesspools, and this cause, with poor
construction, gave rise to stoppages which
still further
aggravated the stagnation.
Decomposition, without the presence of a
plentiful supply of oxygen, evolved offensive gases, which sought the upper air
all possible channels.
Street infor surface water and manholes for
through
lets
cleaning belched forth gases whose malo-
dorous presence was easily recognized. Too
often these odors were noticeable in houses.
To prevent such a
state of affairs various
methods of sewer- ventilation were tried,
which it is unnecessary to describe here.
In modern work of good design sewers are
built with the intention of removing all
sewage immediately before offensive de-
The
has time to begin.
are
as
as
grades
possible,
nearly perfect
the interiors are reasonably smooth to
composition
prevent adhesion of putrescible matter,
and the manholes have perforated covers
to aid in ventilation.
In some cities ven-
70
tilating shafts are provided to
supplement
the manholes, these sometimes being the
soil pipes of the houses, the main trap
being omitted for this purpose. The latter
practice is recommended by some of the
best engineers and sanitarians of the day,
the theory being that by such means well
constructed sewers are kept so filled with
from bad gases, that
no harm can arise if occasionally a trap to
some wash bowl or water closet fails and
the sewer air reaches a dwelling room.
fresh air, and so free
But notwithstanding these opinions the
majority of sanitarians still object to ventilating sewers through houses and insist
upon the main trap.
It seems obvious that
system of sewers, with
4-in. ventilating
50 or 100
ft.
pipe
the separate
small laterals, a
not needed every
in
its
is
on both sides of the
street to
change the air in a 10, 8, or even, as is
sometimes the case, a G-in. street sewer.
The most common practice is to assess the
whole or a considerable portion of the
cost of such small sewers
;
property owners.
Where
upon abutting
done it
this is
71
difficult to say to one man out of
perhaps five, "you must for the general
good omit the usual main trap from your
may be
pipe in order that the street sewer
may be ventilated ; or if you object to
that you may run a separate ventilating
soil
pipe from your house sewer at a point just
outside your main trap to the top of
,ypur
Naturally, most
roof."
men would
object
an alternative, preferring not to
might think, with ample
from
support
engineers and others supto
the lives of themselves
know,
posed
to such
risk,
as they
ana their families, nor to spend money to
avoid such a risk while four of their
neighbors were not called upon for either
To be sure some means
risk or sacrifice.
might be devised to
ventilation
this
through their
would give
the cost of
assess
these extra pipes upon the
where the people refused
rise to
town
to
at large,
allow the
soil pipes,
some
the best, so that the wisest course
be to provide extra ventilation,
perience showed
but
trouble, at
might
if
ex-
necessary, entirely at
town expense, and independently f dwellit
ings.
The matter
of ventilation
is
further
discussed at the end of the next section.
MISAPPREHENSIONS REGARDING SO-CALLED
SEWER
GAS.
Before leaving this subject a few words
seem necessary regarding misapprehensions on the question of so-called sewer gas
and the conveying of disease germs thereby.
And
first,
there
is
no specific and
defin-
sewer gas for which a chemical formula
or combination of symbols can be laid
ite
down. The air in sewers contains in greater
or less degree some of the gaseous products
of
chemical
decomposition whenever
changes are taking place in the organic
matter conveyed by or deposited in the
sewers. This air is harmful if breathed,
same as any other foul air, and to
no greater extent, except for the slight
possibility that it may contain harmful bacteria.
The disease germs which may be
just the
expected in sewage are essentially waterborne instead of air-borne, and develop in
the
human
intestines
rather than in the
73
throat, nose or lungs, and therefore gain
access to man chiefly tli rough food and
drink.
The germs
carried
by
so-called
sewer gas must obviously be air-borne and
from their origin are not likely to be found
in sewage, or if found they would be in
small quantities but while all this is true
it does not make sewer air any more de;
sirable for breathing.
impure
The
air give rise are
evils to
which
invidious, attack-
ing the weak and undermining the physical system of both weak and strong, ren-
dering them more susceptible to various
forms of sickness, notably the zymotic or
Thus it is evident that no
filth diseases.
matter
how much
the nature of the dan-
gers from this source may have been misunderstood in the past they are sufficiently
grave to demand
ward them
off.
all
The
reasonable efforts to
first
aim should be to
prevent, as far as possible, the formation of
foul air within the sewers, and the second
to keep such air as
may form away from
mankind. After good design and construction of the sewer conduits, as such, have
been secured ventilation should be called
74
upon for the introduction of a plentiful supply of fresh air and the removal of 'foul
air to points where it will be diffused
throughout the atmosphere without offense.
Stagnation of air within the sewers must
be avoided.
DR. BILLINGS' OPINIONS ON SEWER AIR
AND VENTILATION.
Before leaving this subject some quotamay be introduced to advantage from
tions
the exhaustive
work
entitled "Ventilation
Heating," by. Dr. John
and
formerly Siirgeon^General U.
S.
Billings,
S. A.,
recognized sanitary authority.
other things Dr. Billing's says
and a
Among
:
The
structed
an ordinary modern, fairly well conand ventilated sewer appears to differ
from the
street air chiefly in
air of
having a higher pro-
portion of carbonic acid.
*
*
*
1C
*
*
Specific pathogenic micro-organisms have not
been found in the air of sewers * * * * As
and soil pipes, the condition
regards house drains
them
in
air
greatly upon whether
depends
cf the
So long as
ventilated or not.
"are
they
properly
75
them are in daily use
these pipes are lined with a moist slimy layer of
organic matter, in which bacteria of various kinds
the fixtures connected with
in immense numbers.
If the supply of air
abundant, these bacteria are mostly aerobic and
the substances produced by their action are, as a
grow
is
and are rapidly carried away, by the
******
rule, odorless
next flush of liquid,
if
soluble.
In hospitals, before the introduction of antisepmethods of treatment of wounds, the pyogenic
tic
organisms were of course very numerous in the
hospital drains, and there are several cases in
which localized outbreaks of erysipelas and unhealthy wound action appeared to be connected
with the passage of the house drain air into the
ward.
******
Distinguished English sanitarians believe that
typhoid fever has been spread through the gases
coming from foul sewers, but I know of no satisfactory evidence of such an occurrence. Diph-
and typhoid fever are diseases which premore extensively where there are no sewers
than in the sewered part of the cities, even where
theria
vail
the sewers are badly constructed.
While I do not attach much importance to sewer
means of transmission of specific disease,
I believe that its continuous inhalation is dangerous,
air as a
owing
to the large
amount of
volatile organic
mat-
76
which it contains, and for that reason, as well
as to prevent the formation of explosive mixtures
and of unpleasant odors, continuous ventilation
ter
should be provided for
and
all
sewers, house drains
cesspools.
In well constructed sewers Dr. Billings
considers ventilation an easy matter, which
can generally be effected by frequent openings to the outer air, and always at each
dead end of a sewer. Special tall ventilating shafts, or ventilation through factory
furnaces or chimneys he considers as of little value, stating that the influence of such
shafts
or chimneys extends only to the
nearest air inlet.
Ventilation through house soil pipes is
approved where the sewers and house connections are properly designed, constructed
and operated, and all are under the control of the
municipal engineer, provided
also the houses
uniform
on a given street are nearly
in height.
Where
opposite condi-
tions prevail, so that the air in the sewers
is bad, and the tops of the soil pipes of one
house would end under the windows of
another, the Doctor thinks that main traps
77
should be placed on all soil pipes and air
inlets and outlets be placed on the sewers
at intervals of 300 to 400
ft.
FEATURES PECULIAR TO THE COMBINED
SYSTEM.
Coming now
system
their
to sewers of the
most
notable
combined
differences
from separate sanitary sewers are their
greater size and the use of catch basins or
inlets for the admission of surface water.
are generally of brick, stone, or concrete, or a combination of two or more of
these, instead of being chiefly of vitrified
They
pipe.
Still
another distinctive feature
is
the provision of storm overflows, by means
of which the main sewers, when overcharged at times of heavy rainfall, may
empty a part
of their contents through a
some water course. At
short conduit into
such times the sewage is diluted by the
rain-water, while the stream which receives the overflow
large vplume. The
is
also of
an unusually
relief thus afforded ren-
ders possible smaller conduits than could
78
otherwise be used without backing up sewage into houses or flooding streets and
cellars
SIZE,
on the lower levels of the
city.
SHAPE AND MATERIAL OF COMBINED
SEWERS.
The
actual size of the sewer of course
depends upon local conditions, as to a large
extent does its shape and material. Where
the depth of flow varies greatly
it
is
de-
sirable to give the sewer a cross-section designed to suit all flows as fully as possible.
Experience has shown this to be an approx-
imation to the cross-section of an egg placed upright on its smaller end. With this
maximum
section a
sewage
is
depth and velocity of
secured for a
minimum
flow,
rendering deposits and stoppages far less
With sewers having a flow more
liable.
nearly constant and equal to their full capof
acity the form may be modified to that
an ellipse, a horse shoe with an arc of a
circle
or
for
some
an invert, or bottom, a circle,
combinaor
modification
tion of these, according to circumstances.
sewers brick is by far the
For the
larger
most common material, both because of
cheapness and of its adaptability to any
Stone inverts are sometimes emshape.
on
ployed
heavy grades, notably where
its
much sand
is
carried in suspension, in or-
der to present a more lasting surface to the
scouring and wearing effect of gritty maConcrete is sometimes used for in-
terial.
verts,
where leakage may be expected, or
movement, but more
in material liable to
commonly
it
affords a foundation for the
The concrete
is also sometimes
extended up the sides of the sewer, and
sometimes completely around it.* If the
brickwork.
material
is
liable to
much
settlement, as in
marshes and bogs, the sewer may be constructed on a timber platform, the latter
sometimes being supported by piles, generally having at least a thin layer of concrete
between it and the invert.
It not infrequently occurs that sewers
rock. In com-
must be constructed through
paratively rare cases this is sufficiently solid
to warrant the use of an unlined tunnel,
where grades are
* See foot note,
i>age
CO.
sufficient
to
permit a
80
rough surface. But generally stones and
uneven walls left after blasting make lining necessary, which is commonly composed of brick, with any spaces behind the
filled with brick or stone
masonry, or concrete.
ring or rings
CATCH BASINS OB RAINWATER INLETS.
A catch basin
is generally placed at each
with a grated opening, or
otherwise, giving the surface water access
to a chamber or basin beneath the sidewalk,
from which a pipe or other conduit leads to
the sewer. Catch basins may be provided
street corner,
with water traps to prevent the sewer air
from reaching the street, but these traps
are liable to lose their seal through evaporation in dry weather, unless they are re-
newed by manual labor from the public
water supply
system.
To prevent
the
carrying of street washings into the sewers
catch basins should be provided with silt
chambers of considerable depth with overflow pipes leading to the sewers, and thus
lessen the bulk of the heavy suspended
matters in the
silt
chamber
to be
removed
"
81
by buckets and carted away
at proper inIn the case of long street blocks
basins may be placed in the centers
tervals.
catcli
of the blocks, as well as at street corners.
STOEM OVERFLOWS.
Storm overflows are simple in theory,
and often so in construction, the main
point being to ensure an overflow into
another conduit when the flow reaches a
certain
elevation in the
sewer.
main and intercepting sewers are
Where
at right
angles to each other the connection is
sometimes so made that the dry weather
flow drops into the intercepting sewer, but
the flood flow, with its greater volume and
velocity, shoots over the interceptor, in
part, and into and through the overflow
sewers.
The lower
portions of
main sewers
formerly discharging at many points into
a stream or lake are sometimes utilized in
this
manner when intercepting sewers are
added.
The
junction of large sewers, and other
complications in combined sewerage systems, sometimes afford ample opportunity
82
and contractor in designand
ing
building masonry suitable for such
for the engineer
places.
Sewers designed to remove surface drain^
age alone are practically the same as combined sewers, without house connections,
and need no discussion here.
PUMPING
STATIONS, RECEIVING RESERVOIRS AND FORCE MAINS.
A large percentage of the sewerage systems of the United States and Canada
operate wholly by gravity, but it is sometimes necessary to pump a part or all of
the sewage of a city. The lifts involved
are usually quite low, so that high-priced
pumping machinery
may
is
not required.
It
be necessary to thoroughly screen the
sewage before
it
passes to the pumps, or to
provide these with valves not likely to be
injured by the miscellaneous bulky substances in the sewage.
The Shone hydro-pneumatic system, used
at the World's Columbian
and
elsewhere in this country
Exposition
and abroad, may sometimes be used to lift
successfully
83
sewage to higher levels. In this system
compressed air from a central station is
automatically discharged into a receiving
chamber with which the sewers are connected, whenever the chamber fills to a
The air under pressure
certain point.
forces the sewage through the outlet pipe.
Where pumping is necessary receiving
reservoirs with more or less storage cap-
may sometimes be provided with
advantage, to equalize the work demanded
acity
pumps and perhaps
down the pumping
of the
to permit shut-
ting
plant at night.
Such
reservoirs are generally covered,
unless in very isolated localties, and may
be ventilated by connecting with the
smokestack, or the gases from the ventimay be conveyed to the furnace fire.
lator
Force mains are generally required in
pumping plants, but some-
connection with
times the latter are so near the point of
outlet, serving as mere vertical lifts, that
the discharge pipes from the pumps cut no
When employed the force main
figure.
will naturally be of cast iron, similar to
that for a water supply system.
84
TIDAL CHAMBERS.
Besides receiving and storage reservoirs
at pumping stations these may be required
where the disposal of sewage is into tide
water under such conditions that it is
necessary to discharge it on ebb tides.
The main distinguishing features of such
compared with these desan arrangement of gates
which will permit of emptying the reservoir in a brief period. These gates should
be easily handled in order to reduce the
cost of attendance.
This may sometimes
reservoirs,
as
cribed above,
is
be effected by mechanical power provided
by the outflowing sewage.
FINAL PLANS AND SPECIFICATIONS.
Before bids for construction are invited
and specifications should be prepared by the engineer. The plans should
be in sufficient detail to make the general
full plans
design and
all
the accessories of the sys^
to bidders, and the
tern perfectly plain
specifications should be explicit
upon every
85
comes within their scope.
Blue prints of the plans and printed copies
of the specifications should be ready for
all inquiring bidders in advance of the
point which
date fixed for opening bids.
The
specifi-
cations are usually accompanied with the
form of contract to be executed between
the city and the successful bidder. In the
matter of specifications and forms of contract the engineer should generally work
in conjunction with an able lawyer, the
city's
permanent legal representative, or
circumstances.
otherwise, according to
Years of experience on sewer work in a
may fit an engineer to cope
all the legal questions
with
single-handed
involved, but in the long run co-operation
with members of the legal profession will
particular city
When difficulties
prove advantageous.
with contractors arise the city's legal adviser is pretty sure to be called in, so it
is
well that he should be consulted at the
start.
Outside of his
the engineer
may
own
particular city
be practically helpless
in legal matters, owing to the wide divergence of laws relating to public im-
86
provements
in
cities
of
the same and
of different states.*
SECURING BIDS AND AWARDING CONTRACTS.
In no department of the engineer's work
money be saved his employers
can more
than in the securing of numerous truly
competitive bids from able contractors and
deciding to whom the contract should
in
be awarded.
On
the proper performance
depends not only the
first cost of the improvements, but the
interest and maintenance account and to
a large extent the successful operation of
of
these
duties
the undertaking. It is more essential to
secure an able and honest contractor than
a low bid; more important that the work
be done well than that it be done cheaply.
The number and character
of the bidders
on a given job will depend upon the importance of the work, the publicity given
to the proposed letting
and the character
* A form of
specification and contract is given in Staley &
Pierson's ''Sepatate System of Sewerage" Prof. J. B.
"
Johnson's " Engineering Contracts ai d Specifications is a
valuable book devoted exclusively to the subjects named in
its title.
8?
of the plans, specifications
In these days of
contract.
and foi-ms of
numerous con-
tractors eager for work at a fair price it is
only necessary to present a clear idea of
the
for
work
to be
done and just conditions
execution to secure an abundance of
its
proposals on almost any job, provided
only the opportunity to bid be brought
to the attention of the possible bidders.
Most
cities
and towns are obliged by law
where
advertise all contract lettings
more than a small cost is involved.
to
It is
generally required that the advertisements
shall appear in one or more local news-
papers and permissible that
in others.
The
the large
cities,
it
be inserted
local newspapers,
even in
reach only a small propossible bidders, almost ex-
portion of
clusively those of the city in which the
papers are published. For this reason,
and because of the better
results
which ex-
perience teaches are to be secured thereby,
thv3 practice of advertising engineering contracts in
growing
course
is
engineering journals
in favor of
late.
is
When
rapidly
such a
pursued the work in hand
is
brought to the attention of the contractors
of a great section of the country, or of the
if of sufficient
importance,
whole country,
instead of to those of one city, and the
number of bids received is in like propor-
But this is not the only advantage.
The wider competition renders far more
tion.
difficult, yes, practically impossible, except under the most corrupt city governments, the growth of a ring of local con-
who through combinations, personal favoritisms and even worse, maintain
prices at a high point, at the same time
tractors
generally doing poor work.
The. bids having been received, they
should be referred to the engineer for tabulation
and recommendation.
From
his
estimates of quantities he can determine the
relative aggregate prices of the several
and from his knowledge, through
acquaintance and inquiry, of the bidders,
and of the probable cost of the work in
bidders,
upon and report the
most favorable bid. As stated above this
is by no means always the lowest bidder,
and it should net be obligatory upon the
question, he can decide
89
award the contract to the parties
do the work for the least
city to
who
offer to
money.
many
Unfortunately the experience of
cities in
having their
officials
award
contracts to favored bidders has led to leg-
enactments affecting some localwhich make it imperative that con-
islative
ities
tracts shall be given to the lowest bidder,
although often the privilege of rejecting
all bids and readvertising is given.
This
is
a long step in advance, but where the
can be trusted time and expense
officials
can be saved both city and contractor by
allowing an award to other than the lowest
bidder, if demanded by the best interests
of the city, based on past records of contractors and the danger of poor work at ex-
Such a course, aside
cessively low prices.
from obliging a city to accept an undesirable bid, discourages designing contractand those who, in their eagerness for
work, figure too low, and does not call
ors
upon responsible men, of good judgment,
to be to the trouble and expense of
putting in bids the second time.
90
THE PROPER EXECUTION
OF THE CON-
TRACT.
The
contract having been awarded and
construction started, it devolves upon the
engineer to give the contractor all necessary lines and grades, and any information
needed and not provided in the plans and
specifications. It is also his duty, both personally and through his inspectors, to see
work is done according to the
This requires the
and
plans
specifications.
most careful and conscientious attention on
the part of able men. Every detail of construction must be watched with an eagle
eye and no work not subject to complete
examination after it has been executed
that the
should be allowed to proceed in the absence of the inspectors. On pipe work or
conduit construction, especially, one inspector should never be called upon to look
after work in more than one street at the
same time. Pipe and brick must be examined with the greatest care, the former
Cement should be subpiece by piece.
to
test
to show its fitness for
jected
proper
01
the use to which
it is
to bo put.
This
re-
quires at least a simple testing laboratory,
and the provision of a fully-equipped one
is
money well spent where naich work is
to
be done. After the sewers are completed
they should be tested for obstructions, the
small sewers by passing a ball through, or
otherwise, and large ones by having a man
go through them.
REGULATIONS FOK THE USE OF SEWERS.
These include
all
necessary precautions
for the prevention of obstructions, chief of
which, perhaps, is the proper laying and
joining to the street sewer of house conThis work is often, if not gennections.
done by plumbers, but all such
should work under a license, revokable for
erally,
non-compliance with city and town ordinances, and should be under the supervision
engineering, sewer or health department. The size, grade and material of
house connections should be specified in the
of the
above regulations, and in order that prosecutions and punishments may be possible
for offenses against these and other rules
92
necessary to have an ordinance or or.
dinances passed, embodying all the neces-
it is
sary rules and regulations and providing
penalties-.*
OPERATING THE SYSTEM.
The sewers completed
their operation is
nearly always very simple, especially where
pumping or purification is not necessary.
A superintendent of
in
sewers, in fact
if
to
not
have
name,
generally employed
general charge of the sewerage system.
This official often oversees house connecis
and frequently has charge of minor,
and sometimes of important extensions of
the system.
He removes stoppages and
looks after flush tanks and other devices
tions
for keeping the sewers clean. If pumps
are used these are likely to be in sole
charge of the pumping engineer> although
he
may be under the superintendent.
Where purification is employed a man independent of the superintendent may or
may not have charge. All purification
*
A model
tem
ordinance will be found in the
of Sewerage. "
' '
Separate Sys-
93
plants should be under the immediate direction of the most competent men attainable, within
reasonable limits, as intelli-
gence and knowledge are absolutely essential to their
continued, and often to their
temporary success. Politics and political
berths should be kept clear of this
depart-
ment
of the sewerage system,
other
it
should be from
if
from no
all parts.
SEWERAGE COMMITTEE, BOARD OF PUBLIC
WORKS OR CITY
The above
COUNCIL.
considerations suggest the
question, should the construction and operation of a sewerage system be entrusted to
a sewerage committee
entirely independent
of other departments of
to
city
government,
a board of public works
charged with other
municipal improvements of an engineering
The
character, or to the city council ?
answer to
this, like that to so
many
otln-r
questions already raised in this volume, is
that local conditions often determine what
is best.
It is
cities
interesting
and towns,
as
to
note that
ck-arly
English
in Dr.
shown
Albert Shaw's " Municipal Government in
Great Britain," manage in an admirable
practically all their public works
through their city councils and committees
of the same, always relying, however,
upon able and experienced engineers and
others for technical advice and the details
manner
In this country the mistrust
of operation.
of city councils has been, and largely is
PO great that the first thought of tax-payers
on undertaking the installation or ex-
tension of
to entrust
some important public work is
it to a special and
independent
body of men.
The English system has the advantage
*-
that all public improvements are thereby
carried out with due consideration to their
r
relation to eSeh other
and to the finances
A
of the^ity as a whole.
board of public
works entrusted with streets, sewers, water
.
and lighting plants, if the two latter be
operated by the city, would be a close approach to the English plan, and would in
many instances have its advantages over
that plan under American conditions.
Generally
speaking
independent
sewer
95
commissions,
right
men
if
only
and
it
is
composed of the
which counts
have built and are
this
more than any system
managing sewerage systems with good results in this country.
But from the nature
of the case they
cannot always so plan
their work, for instance, as to interfere as
as possible with
good street pavebecause
have
no control over
ments,
they
the time and place of laying such. Whatlittle
ever the system, an able city engineer, or
engineer of the sewer department, should
be given the practical settlement of all en-
gineering questions.
SEWAGE PURIFICATION
IN
ITS
GENERAL
ASPECTS.
Having
treated the other phases of the
subject as fully as the space available will
permit, there remains for consideration the
important matter of sewage purification.
This has been reserved to the last, except
for the incidental references to
it
already
made, because it is quite complete in itself
and demands independent handling. The
main principles of sewerage construction,
96
from disposal works, have been established for many years, but the best
aside
means of rendering sewage
fit
to discharge
into water courses or other bodies of water
not suitable for the reception of crude sew-
age are problems of yesterday, to-day and
even of the future.
Enough has been
settled, however, to render no longer valid
the plea that sewage purification is as yet
in too experimental a stage to forbid efforts
We know to a certainty
how sewage may be rendered harmless.
in that direction.
Further knowledge will probably be in the
line of making present processes do more
work without additional cost. The facts
are, that the two older systems of sewage
purification
and chemical
for
now
in
use,
precipitation,
land treatment
were practised
years in a blind rule o'thumb
way, and often with good results, before
many
their
fundamental
covered.
Since
principles
were
dis-
the
discovery of these
principles, or natural laws, we can do
nearly always what formerly was done only
occasionally.
Blood pulsed through man's veins for
97
countless
centuries
before
Harvey
dis-
covered the law of circulation, and many
maladies incident to blood and circulation
were helped or healed in utter ignorance
of the law, but since and by means of the
discovery what a revolution there has been
in
medicine and hygiene
!
We
look for-
more progress in these particulars,
but we do not for this reason hesitate to
ward
to
avail ourselves of all that has
been accom-
But this is exactly what some
plished.
do in the matter of sewage
would
people
purification, or at least
they offer as an
excuse that the science
in too tentative a
is
stage to warrant the adoption of any plan
as yet, their real motive too often being
a desire to keep the municipal purse strings
pulled tight.
What
is
most needed now
is
not
new
processes, but the careful carrying out of
well-known methods, with observations on
the results obtained under all the varying
which naturally arise in
and under varying conditions at the same works.
We have a
host of suggestive and many conclusive
circumstances
different localities
deductions drawn from careful and longcontinued experiments, both at home and
abroad, but we need, particularly in Amerto have more of the scientific spirit
and method which have made the laboraica,
work
tory
so
successful
applied to
the
daily operation and study of actual sew-
Instead of caviling at the
age works.
uncertainties of sewage purification those
who raise questions might better take their
turn at efforts to perfect, simplify and
cheapen the already admirable processes
now
available.
They may
rest
assured
that the worst yet attained by intelligent
effort along the new lines of work is
infinitely better
tion
than the shameful prostituand lakes now going on
of streams
throughout this broad land, a marring of
beautiful face of nature, rendering
limpid waters black and repugnant, chang-
the
ing their refreshing breezes to sickening
odors, while life-giving water is made a
death-dealing
poison,
and
all
through
sewage pollution.
Before taking up sewage purification in
it will be well to consider what sew-
detail
age
from the standpoint of the chemist
bacteriologist, and what should be
is,
and
expected
or
purification.
it appears at
way of its
and as
when
fresh,
Sewage,
the mouth of an outlet sewer,
desired in the
a cloudy,
opaque grey
with some large particles of suspended matter not easily broken up in
is
generally
liquid,
transit, as
orange peels, rags, paper and
various nondescript articles too numerous
It very often has a faint,
to mention.
musty odor, and
in
both looks and .smell
sometimes quite comparable with the
of
suds-water
family
laundry work.
of
the
is
all
sewage
Nearly
simply water,
the total solids in supsension averaging
is
perhaps 2 per 1,000, of which a half
may be organic matter. It is this 1 part
in 1,000 which is to be removed or so
changed
in
character as
ttfW 'rendered
harmless.
These facts regarding the composition
sewage are far different from the
popular conception, which pictures a vile
mass, indescribable in appearance and odor.
Such ideas are gained in part from the
of
100
contents of cesspools and from improperly constructed and neglected sewers,
known
but they arise largely in vivid imaginations.
They would be applicable in many
sewage allowed to stagnate and
take on putrescible decomposition, as happens in cesspools and obstructed sewers, or
where the sewage stands on the surface of
respects to
poorly graded land disposal areas, or
accumulates in any similar manner before
being purified.
The greatest danger from sewage is in
the harmful bacteria which it conveys,
but even these are not to be feared if kept
out of the
human
system, to which they
rarely gain access except through water
used for domestic purposes or in connection
with milk supplies.
Generally speaking, sewage swarms with
bacteria, engaged, when sufficient oxygen
is present, in the laudible occupation of
converting unstable organic matter which
might become offensive into fixed mineral
compounds
of a wholly unobjectionable
These plants may
millions to the teaspoonful, and
character.
number
yet be
101
wholly invisible, so minute are the organisms and so hidden is the mighty work in
which they are engaged. To isolate the
harmful from the harmless with certainty,
if
at all, is
an achievment for some future
Pasteur.
The organic matter and the bacteria always accompany each other. If all the
bacteria should be removed or killed, but
some of the organic matter remain, another crop of microbes would develop as
if by
magic as soon as seed was sown, although the renewal of disease germs in
their orginal quantities would
rarely, if
ever, occur except from a source the same
as or similar to the original. But, remove
all the organic matter and all the bacteria
food is gone and without food death
comes swiftly, even though the bacteria
be legions.
From
the above it may be inferred that
sewage purification processes are valuable in so far as they remove or
change
the composition of organic matter. Mechanical straining, sedimentation and chemical
precipitation are largely removal processes,
all
102
while septic tanks, broad irrigation, intermittcnt filtration, contact beds and percolating filters change the putrescible organic matter into stable compounds.
Either form of land treatment may be
employed where practically complete purification is desired.
Straining or sedimen-
remove only a small portion of
the organic matter. Chemical precipitation and the use of septic tanks will do
more, but must be supplemented by irrigation or intermittent filtration where a
high degree of purity is required. Contact beds and percolating filters, generally
tation will
preceded by septic tanks, but sometimes
by sedimentation or chemical precipitation instead,
may be
relied
upon
to pro-
duce a non -putrescible effluent relatively
free from suspended matter, but generally
high in bacteria. Aeration may also be
be called in to supplement other processes,
but the part which it can perform is far
more limited than is supposed by many.
The
object of sewage purification, then,
being the removal of organic matter, and
certain modes being available for the
103
partial or complete
this end, the question
accomplishment of
which is the most
is,
Like nearly all the other queswhich
have arisen in the course of
tions
this book, and like most other questions in
desirable ?
engineering, other sciences or the arts,
The degree of
there is no one answer.
purification required and the local conditions which make one system cheaper than
another in construction and operation all
have their weight in selecting a system of
disposal.
It sometimes happens that a partial removal of the organic matter contained in
sewage is ample, in which case the 20 to
30 per cent., more or less, that can be
accomplished by either sedimentation or
straining will be sufficient. If better results are
wanted and some 50 per
slightly more, of
the sedimentation
may
cent., or
is
needed,
be accelerated by
purification
the use of certain chemicals, which constitutes chemical precipitation, or the septic
tank
may
be employed.
If neither of
these will suffice, the effluent from either
process, or in fact from sedimentation or
104
straining,
may be applied to a sewage
intermittent
lating filters
farm,
contact beds or percoor where plenty of hii'd is
filters,
;
available, all previous treatment
dispensed with and intermittent
may
be
filtration
or irrigation, commonly known as sewage
farming, or a combination of these two
land processes, may be brought into requido all the work. Obviously where
sition to
only partial purification is required there
be a wide range of choice between
may
the methods named.*
Although the object of sewage treatment
may sometimes be the removal of bacteria,
the chief aspect of most of the sewage
works now in operation is to prevent nuisances in the nature of foul sights or odors.
Where public water supplies are involved
the aim
is
to keep the
sewage
out, or to
purify the water, or both.
SEDIMENTATION.
This
is
effected
by allowing the
sus-
See " The Partial Purification cf Sev age," by C< 1. Geo.
E Waring, Jr., Ewjin- ering Aevsof Jau. 4. 1894, for an eit<-ndt d d.scussion of the subject named in the title just
quoted.
*
105
pended matters to
settle
tanks.
in
The
partially clarified liquid is drawn off, leaving the solid matter, called sludge, at the
bottom for subsequent disposal. This proas has been intimated, is akin to
cess,
chemical precipitation, so the shape of the
tanks, the relative merits of continuous
and intermittent settlement and the treatment of the sludge will be taken up later
on.
Experiments with sedimentation at Lawrence, Mass., during the last three months
of 1893, indicated a subsidence of 18.2 per
cent, of the
albuminoid ammonia and 12 per
cent, of the bacteria in the crude
during a period of four hours.
experiments in 1894 showed a
sewage
The same
much better
average for organic matter, as measured
by the albuminoid ammonia, but about the
same
results for bacteria, the respective figures being 30 and 14.6 per cent. In 1895,
there were removed 48 percent, of the total
albuminoid ammonia, and 31 percent, bacabout 35 per cent, of each.*
teria; in 1897,
*
Reports of the Massachusetts State Board of Health,
1893, p.
41,6,
f^r 1894, p. 454, 1805, p. 451,
and
1897, p. 416.
106
These experiments were discontinued early
tinned early in 1898.
It is
hard to imagine conditions in actual
practice which would warrant the construction of tanks of sufficient capacity to
admit of four hours settlement where only
a 30 to 40 per cent, removal of the organic
matter could be expected. With smaller
tanks the work done would of course be
so sedimentation is not likely to be
employed except where a small amount of
less,
purification at a slight expense is all that
is
needed.
MECHANICAL STRAINING.
This admits of a great variety of practice,
ranging from attempts to remove
and other large substances to
an approximation to intermittent filtration.
rags, paper
Wire
screens or filters of various materials
may be employed. Generally little is accomplished, but in well-constructed and
operated plants screening or straining may
be an important factor in the purification
effected.
filtration,
As a preliminary to intermittent
coke strainers, or thin filter
107
were used at Lawrence during the last
seven months of 1894, removing 52.4 per
cent, of the albuminoid ammonia in the
original sewage.* These beds ranged from
IK to 8 ins. in thickness during the experi-
ments, and the sewage passed them at an
average rate of about 345,000 gallons a
day for six days in the week. A depth of
is given as desirable and it
estimated that when straining ordinary
sewage from 5 to 8 cu. yds. of coke would
6 ins. of coke
is
have to be removed per 1,000,000 gallons
filtered.
Mechanical straining through coke or
sand at the rates named might perhaps
more properly be termed continuous rapid
filtration.
Some
of the better of the re-
sults given are about the same as those
secured in the same experiments by means
of chemical precipitation, using 1,000 Ibs.
of sulphate of alumina per 1 ,000,000 gal* Keport of the Massachusetts State Board of Health for
The rep rts of the Massachusetts State Board
1894, p. 455.
of Health from 189t to 19u2, inclusive, contain accounts of
various further experiments with coke, anthracite and
bituminous coal as screens. From 3 to 15 ins. of these materials, working at rates of 1,000,000 gallons a day and upvards, r< moved from 32 to 62 per cent, of the total albumincid aii iiionia.
108
Ions of sewage, or 7 grains per gallon,
allowing four hours for precipitation.
and
The
mechanical straining usually employed is
insignificant in results compared with the
above. The same may said of sedimen-
Both processes in these experias
well as the chemical tests carried
ments,
on simultaneously, were intended to facili-
tation.
tate
and
relieve the
work
of filter beds.
CHEMICAL PRECIPITATION.
Sedimentation alone removes only such
suspended matter as will sink by its own
weight during the comparatively brief
time which can be allowed for the purpose.
Some
of the lighter matters
may
of course
be carried down by the heavier particles,but
the total results are comparatively small.
If the process could be continued long
enough, practically all matters in suspension
might be removed, but those in solution
would remain and putrefaction might begin in the sludge,
if
not in the sewage
By adding
cer-
tain substances chemical action sets in
and
undergoing
clarification.
precipitation occurs.
Some
of the organic
109
substances are brought together by the
formation of new compounds, and as they
masses they carry with them
other suspended matter. As in sedimentation or straining, a part of the bacteria
fall in flaky
removed by mere entanglement, while
every grain of organic matter removed
are
decreases
supplies,
by so much the
bacterial food
and thus the potential number of
bacteria,
A
great number and variety of chemhave been employed as precipitants,
but years of experience have resulted in
icals
the general adoption of lime, sulphate of
alumina and some of the salts of iron,
more
especially ferrous sulphate or copperas, or a combination of two of these, as
best suited for the chemical precipitation
of sewage. The character of the sewage
and the relative cost of the several chemicals in a given locality should be deterLime is cheap almost
mining factors.
everywhere, but the comparatively large
quantities required increase greatly the
amount of sludge. Sulphate of alumina
is not so
readily obtained, and often must
110
be transported such a distance as to make
freight rates quite a factor in its cost. It
often used in conjunction with lime,
is
less amount of sludge than
lime alone and in some cases doing more
effective work.
Where either an acid
producing a
sewage or one containing iron salts is to
be treated, lime may be used without the
sulphate of alumina and a considerable
saving effected.
If the acid or iron salts are
discharged at intervals the sewage must be
tested from time to time to determine
when
to
modify the amount of chemicals
A
very interesting
example of this sort is found at Worcester,
Mass., where large quantities of acid and
artificially applied.
iron are discharged into the city sewers
from manufacturing establishments.*
In buying chemicals of any kind great
care should be exercised in determining the
available amount of the active agent, as
the amount of calcium oxide in lime, or of
alumina in sulphate of alumina, different
products varying greatly in this respect,
See Engineering Xeu-ss, No. 15. 1F90, and July 28, 1892
and Baker's " Sewage Disposal in the United
;
also Rafter
States."
Ill
notably the lime from different quarries
and
kilns.*
The chemicals should be added
to
and
thoroughly mixed with the sewage before
the latter reaches the settling tank.
The
be effected in nearly all cases
by projections into the channel leading to
mixing
may
the tank, called baffle plates.
Experience has demonstrated that the
tanks should be long and narrow and that
they should be operated on the continuous
j
The
rather than the intermittent plan.
width of the tank may be, say one-fourth
its
length.
In the continnous plan the
sewage is constantly flowing into one part
of the tank and discharging from another
more or
in a
less clarified state.
In the
intermittent system a tank is filled and
then the flow turned elsewhere, allowing
the sewage in the first tank to come to
Where the continuous plan is used
rest.
'the
sewage generally flows through a
set
* For tl e theory of the actions of the various re-agents,
the qiiHulities employed and their costs, both in experimental and practical work, see Rafter and Baker's "Sewage Disposal i:i the United States." Tl>e brief limits rf tl.i-v lume
render! possible much more than a discuhsion of g. neral
principles; detailed ninires, UDHCCOII pam d by ihn data
upon \Nhieh they are based, am apt to be misleading.
i
112
of tanks without change of gates or other
interruption until one compartment needs
cleaning. This compartment being cut out
and
left to itself for
a while, the clarified
then drawn off gradually from
sewage
the top through a hinged pipe, the upper
and open end of which takes sewage from
the surface on opening a valve in the horis
izontal portion of the drain pipe beyond
When the effluent is
the hinged joint.
decanted to the top of the deposited sludge
the valve just mentioned is closed and
another one, in the sludge pipe, opened,
allowing the sludge to flow out, or to be
pumped out for final disposition. The
tank should then be thoroughly cleaned,
after which it may be treated with disinfectants or deodorants, if desired, before
being again put in use.
The
disposition of sludge
is
one of the
most vexed problems connected with sewage disposal. It is a pasty, semi-liquid
mass, ordinarily containing from 90 to 95
per cent, of water and 10 to 5 per cent, of
solid matter. The most common method
of disposal, and perhaps the one most gen-
113
erally available and
satisfactory, is to
much
as
as is possible out
water
squeeze
of the sludge by
means of presses designed
This greatly reduces the
bulk of the material. The liquid from the
press goes back to the tank for further
for the work.
treatment.
The sludge cake,
as it is called,
may be handled easily. It is sometimes
burned and sometimes hauled away by
farmers for use as a fertilizer. There have
been great expectations on the part of projectors of chemical precipitation works
that the farmers would vie with each other
in securing the sludge, and even pay good
money
for
it.
The general
experience,
both in this country and abroad, has been
that a city is lucky if it is able to induce
anyone to haul the sludge away for it.
In some cases peat or some other absoris mixed with the sludge to render it
more easily handled and removed in, bulk.
Again, it is run out on the surface of coarse
sand and gravel beds and its liquid parts
reduced by draining and drying. Some of
the difficulties connected with this last
bent
method are
:
114
In wet weather little drying takes
the colder mouths the
place, and during
in considerable quanaccumulates
sludge
labor must be emManual
tities.
(2)
(1)
ployed to remove the sludge from the
draining and drying beds. (3) Where
chemical precipitation is employed suitable
land, in character and extent, is often not
to be had.
At Birmingham, England, large volumes
of sludge are pumped through force mains
distributed
through
portable
pipes
to
and covered with earth.
There remains another method available
for some seaside cities, and that is dumping in the ocean by means of large steam
sludge ships. Thousands upon thousands
of tons are so disposed of from the sewage
works of London and Manchester, England, and Glasgow, Scotland.
The capacity of the settling tanks is
often the chief factor in determining the
cost of installing precipitation works.
As-
suming that the sewage should be one hour
in passage through the tanks, and that the
maximum
flow
is
twice the average, pro-
115
vision
must be made for one-twelfth the
to-
tal daily flow, where house sewage only is
treated. This makes no allowance for throw-
ing out a portion of the tanks for cleaning
or repairs. It would certainly be erring
on the safe side, if at all, to provide a tank
capacity equal to one-eighth the total maximum daily flow. Where sewage from a
combined system
is
treated, it is of course
practically impossible to provide a tank
capacity sufficiently large to treat all the
sewage. Either the excess of storm water
must be discharged into natural water
courses along the lines of the sewers or
by the works without treatment. If
pass
ample tank capacity
is
available
it
may be
possible to treat all the sewage during the
first part of a moderate rain.
This would
mean the purification
of the foulest portion
and other washings, after which
many localities it might be admissible
of street
in
to forego all attempts at purifying the
sewage, as the results which could be ob-
tained would be comparatively insignificant.
During such a heavy rainfall the
sewage of a combined system would be
116
times diluted, and where the effluent
from the works discharges into a stream
many
the latter
ume.
is
also greatly increased in vol-
where purification
in
connection
with a new sewproposed
the
erage system
separate plan will pracIt is evident that
is
tically always be adopted.
tion plants in this country
Most purificahave been built
same time
as the collecting system,
such cases the separate plan has
used.
Worcester, Mass., was forced
to adopt purification after many miles of
combined sewers had been built, and after
at the
and
been
it
in
had converted a brook with a consider-
able drainage area into an outlet sewer.
Its later sewers have been built for house
wastes only, and hundreds of thousands of
dollars have been spent since the sewage
works were built in excluding
water from the sewers.
THE
The
surface
SEPTIC TANK.
septic tank, as
we now know
it,
has
been developed since 1894. In effect, it is
a sedimentation basin, so designed and
operated as to lessen the sludge deposit by
II
1
dissolving a portion of it and by reducing
another portion to gaseous form. This re-
duction or hydrolysis of the sludge is
brought about by anaerobic bacteria, which
work
in the absence of air,
and are thus
directly opposed in character to the aerobic bacteria or nitrifying organism of sew-
age farms, intermittent
and percolating
filters,
contact beds
Since inorganic
matter is not acted upon by the bacteria,
its exclusion from the septic tank is desir-
To
filters.
chambers are
which
the
sewage passes
provided, through
on its way to the septic tank. The high
specific gravity of the sand and other min-
able.
this end, small grit
eral matter in the
sewage causes much of
to sink in a brief period of time, while
the remainder of the suspended matter, init
cluding the lighter organic sludge, passes
into the septic tank.
Since the admission
of air to the septic tank would tend to displace the anaerobic bacteria by aerobic,
the tank inlets and outlets are generally
submerged a foot or so beneath the normal
sewage level. The tanks are made long
and narrow, thus affording time for sedi-
118
mentation, and have a sewage depth of 6
For convenience in removing
to 9 feet.
sludge, their bottoms slope to one or more
sumps or gates.
Whether or not
septic tanks should be
covered has not been universally agreed.
It is held by some that a roof, excluding
light
and
cessity,
air, is a great help, if not a neto the highest efficiency; while
others argue that roofing is unnecessary
to full bacterial action, except in very cold
climates, and that a roof need be provided,
at all, only for such tanks as are near
if
dwellings or much-traveled highways, and
which on that account might give offense
to residents or passers by.
Any
fairly water-tight material
may be
used in constructing septic tanks ; probably
concrete, either plain or reinforced, is now
used more commonly than any other material.
The
roof, as well as the walls
and
bottom, may be of concrete, or where low
first cost is an object, wood may be used
for roofing.
Since the action of the septic tank is due
tc anaerobic bacteria, while further purifi-
119
cation
is
effected
by aerobic germs, and
since the septic effluent
is
not only high in
germ contents, and nearly if not
available oxygen, the septic
without
quite
anaerobic
effluent is
sometimes aerated before being
passed to
filter
beds.
Weirs over which
the effluent flows in a very shallow stream
or a series of overflow steps are used for
purposes of aeration.
The amount of sludge removed by septic
tanks cannot yet be safely predicted for a
given sewage works until actual tests have
been made.
show wide
Such figures as are available
variations at different localities.
No
one should be deluded by observations
amount of sludge remaining in a
septic tank, since large volumes of sludge
of the
in a finely divided state may pass off in
the effluent. Volume for volume, however,
this finely divided
suspended matter will
make
far less trouble than the sludge from
ordinary settling tanks or from chemical
Some of it is already
a mineral ash, subject to no further organic
change, and the balance is partly reduced
precipitation works.
120
to mineral matter and also to food for the
low forms of organic life.
Such sludge as remains in septic tanks
may be disposed of by the means already
described.
In some cases, probably due to the charsewage or to improper opera-
acter of the
tion,
when
sludge from septic tanks is offensive
first exposed to the air.
Under such
a condition the sludge disposal should be
carried on at a remote point, or the sludge
should be buried quickly a few inches
beneath the earth. Investigations should
made to determine whether the
odors cannot be prevented by a change in
the design or operation of the tank.
also be
Were
it
within the scope of this book,
and less free from conflicting claims, it
would be interesting to attempt to trace
the history of the septic tank. The subject involves claimants in Great Britain,
the United States,
and
Germany and France;
early tanks installed and
used with success, though with little or no
also
many
understanding of the principles involved,
long before the name septic tank came into
121
use.
the
It is now generally recognized that
man who gave the septic tank its name
and brought it into scientific prominence
was Donald Cameron, of Exeter, England,
but up to early in the year 1905 it was not
generally conceded that Cameron's work
entitled him to patent control of the septic
tank process. The question was then in
the courts of the United States for trial,
but had never been legally raised in Great
Britain, so far as the author of this book
could learn.
" ELECTRICAL "
AERATION.
PROCESSES.
ARTIFICIAL
While the oxygen of
the atmosphere
be
made
one
of
the
may
greatest agents in
some
and others
writers
purifying sewage,
have laid too much stress upon the value
of artificial aeration.
Mountain streams,
which tumble over rocky beds, are noted
for their purity, and this has been attributed
largely to the aeration which the water
receives.
It
should be remembered that
122
the waters of such streams are generally of
a high degree of purity to start with, often
being little different from rainwater just
from the clouds, and that the aerating
It
is quite commonly a long one.
has been further observed that even badly
process
polluted streams show greatly improved
chemical analyses at points a number of
miles below the source of contamination.
But
here, sedimentation,
and the action of
both animal and vegetable life in their
more minute forms, play a notable part in
the purification process, and the timeelement is also important.
It has been well established by the
Massachusetts State Board of Health in
its
Lawrence work that the two
essentials
for the removal or transformation of the
organic matter in sewage are oxygen and
time, where dependence is placed on a
nitrifying or oxidizing process.
The
time-'
element has been largely ignored by some
theorists, a few of whom have put their
theories into practice.
Purification plants
have been built, and more have been projected, in which the great reliance has been put
123
upon
artificial aeration, either
by forcing
the sewage or by causing the
latter to fall through the air in drops or
air into
This has been accompanied
streamlets.
by rapid
sand.
filtration,
generally
through
Now aeration
of the sewage, or of
the filtering material, may be employed as
an aid to sewage purification, but like all
things else it has its limits. It can maintain a supply of oxygen which is of use up
and this will be of value.
All in excess of this amount is of no
to a certain point
value, and
unless time
even
is
oxygen and
The
this
is
not
of
use
given for the action of the
of the nitrifying organism.
latter develops rapidly in the presence
oxygen and organic matter, transforming the latter into mineral compounds.
These facts are overlooked by some of the
of
promoters
o.f aerating processes,the assumpseeming to be that given a plenty of
the desired work will be accomplished
tion
air
The facts are that sewsoon
loses
all
the available oxygen
age
taken up by it during aeration and needs
to be aerated again and again until all
.almost instantly.
124
The
the organic matter is transformed.
time-element can best be secured, almost
invariably in some form of filter bed.
Perhaps there is an even greater
so-called
regarding
misunderstanding
methods of
electrical
sewage purifiThese processes, which have
cation.
met with but little favor, simply prepare by electrical means some chemical
agent which performs all the work accomplished and might be obtained in some
other manner, although possibly at greater
expense. In the Woolf and Hermite processes either sea
common
water or a solution of
according to the readiness of
one
or the other, is partially deobtaining
an
electric current, and sodium
composed by
salt,
hypochlorite
is
formed.
The
mixed with the sewage and
dorizer and germicide, its
solution
is
acts as a deoefficiency de-
pending on its strength. The organic
matter remains in the sewage and is subject to secondary decomposition later on.
The product obtained by this process
might be of value under certain conditions,
125
the same as other good disinfectants are,
but there seems to be no reliable inform-
show that anything further
be
can
expected of it.
The direct treatment of sewage by electricity has been talked of for some time
but it still remains a dream.
ation to
BROAD IRRIGATION OR SEWAGE FARMING.
Where sewage
is
applied to the surface
ground upon which crops are raised
the process is called broad irrigation, or
sewage farming. The practice is in most
of the
respects similar to the ordinary irrigation
of crops with clean water, the sewage being applied by a variety of methods, ac-
cording to topographical and other natural
conditions and the kind of crops under
cultivation.
The land employed
for this
method of
purification should preferably be composed
of a fairly light, porous soil. The crops
should be such as require, or at least
develop best under a large amount of
126
Where the soil is heavy and
and the crops cannot stand much
water, the sewage must be applied sparingly, and so a large amount of land
As
and much labor must be provided.
moisture.
wc-t,
may be prepared at
small
expense it is somecomparatively
times feasible to make use of land not so
broad irrigation areas
well suited to the purpose as might be
it
can be obtained
desired, provided
cheaply enough and too much stress is
not laid upon the raising of crops. The
less the attention
paid to cropping, gene-
rally speaking, the greater the
amount of
sewage which can be put on a given area
of land.
Wet, clayey soils can take but
under any circumstances,
little sewage
but sometimes improve with cultivation
and the application of sewage.
The
application of an average of from
to
5,000
10,000 gallons of sewage per day
to one acre of land is considered by many
On the basis
liberal allowance.
100 gallons of sewage per head of
population this means that one acre of
as a
of
127
land
sufficient for a population of
is,
50 to 100 persons.
the crops
kind there
if
More could be
from
purified
would stand it, but for each
if
is a limit which
passed
means the destruction of the
crop.
Allowing even 10,000 gallons of sewage,
or 100 persons, to an acre in a city of 20,000
inhabitants would require 200 acres. To
find
suitable
land
at
a low price near
not always easy. The larger the
the
city
greater the difficulty. Labor, too,
is a big item in sewage
farming on this
cities is
side the Atlantic, especially near cities.
As a partial offset to this, great cities
afford excellent and never-failing markets.
Another great obstacle to adequate finanreturns from
sewage farming in
America is the deplorable fact that
political ends and not business principles
govern in large numbers of our cities,
cial
though there is good reason to predict
a
great
change in this respect ere
Where
such conditions do prevail,
long.
however, the positions of both superintendents and laborers on sewage farms are
ulinost sure to be considered rewards for
128
and encouragements to party service, with
results most unfavorable to the enterprise
in hand.
Sewage farming means the selling as well as the raising of crops, and
perhaps of live stock, and so requires
business ability and agricultural skill.
The latter must be accompanied with the
faculty of handling considerable bodies of
men.
These
apparently
discouraging
ments are meant rather
as warnings.
state-
They
are necessary because of the glowing representations which have been made regard-
ing the profits of sewage farming by those
who have not looked at all sides of the
am
not unmindful of the resewage farming abroad, but Euro-
question.
sults of
I
pean conditions are far different from ours.
Many of the European farms are most admiral ly managed, both from an agricultural and business standpoint, and not a
few of them have
to
contend
far less favorable than
with
soil
could be found
United States.
American
I do not say that an
city could
in
many
sections
of the
not conduct so great an enterprise in a
129
creditable manner, for
we have many
well-conceived and well-operated municipal works of great magnitude. I do say
that high prices for land near large cities,
costly labor, a constant warfare against
corruption with too frequent surrenders,
and our sudden and complete changes in
government all make sewage farming more
difficult
here than abroad.
For the present, sewage disposal cannot
be accomplished in this country at a profit.
It is sometimes possible to regain through
the raising of crops a part of the expense
entailed in removing and purifying sewage,
and this is the only method by which any
considerable portion of the expense has yet
We
been recovered here or elsewhere.
should be thankful for the day of small
things, and wherever a revenue can be obtained from irrigation area or filtration
beds our efforts should be to secure it. But
the logic of figures will often show that
some method of disposal that carries with
no financial returns is the cheapest, in
which case instead of crying over spilt and
wasted sewage, we may laugh over a sav-
it
130
ing in capital, interest and maintenance.
Wherever
irrigation,
pure and simple,
the application of water to crops
for the sake of moisture, can be practiced
that
is
to advantage, sewage farming should receive serious consideration, for in such
localities every drop of water is valua-
As ordinary irrigation may yet be
used in the East as well as in the West,
ble.
(it is already practiced to some extent in
the South) the use of sewage for mere
watering as well as fertilizing may some
day be seen -here and there throughout the
length and breadth of the land. This is a
subject which demands careful investigation and perhaps might be taken up with
advantage by some of our agricultural experiment stations and by any live official
in a position to do so.*
* For an article on "The Use of
Sewage for' Iriigation in
the \\ est " ste Angineei ing iYew for .Nov. 3, Ife9j the substance of the article is a.so given in Kafter and Baker's
"
Sewage Disposal in the United States. A later treatment
of the subject may be found in "Sewage Irrigation," Nos.
3 and 22 of Water Supply und Irrigation Papers of the U. fc.
Geological Survey, by Gto W. Rafter, M. Am. Soc. C. E.
In March, 1905, the author cf this book visited the sewage
farm of Pasadena, Cal., and also land to which some of the
sewage of Los Angeles is applied. As a result, he is more
than even convinced of the wisdom of using sewage for ir;
1 '
rigation wherever water is scarce.
131
SUB-SURFACE IRRIGATION.
Before passing on to intermittent fila word should be said regarding
tration
sub-surface irrigation. The system is capable of use on a small scale, chiefly for
private dwellings, various public institutions and small communities where for any
reason surface disposal would be objectionable.
Tiie
sewage
agricultural drain
joints,
is
distributed through
laid with open
tiles,
and placed only a few inches below
Provision should be made
the surface.
for changing the disposal area as often as
the soil
may require by turning the sewage
into sub-divisions of the distributing pipes.
The sewage
is
generally discharged auto-
matically at intervals on the filling of a
tank to a certain height. Where surface
application can be practiced
erally, if
it would gennot always, be preferable to this
system.
INTERMITTENT FILTRATION.
This method of sewage purification
is
capable of producing the highest results
132
under favorable conditions, and those conditions prevail perhaps more widely in this
country than like ones for any other system.
The process is a most simple one.
With a competent man in charge large
areas of beds can be operated with cheap
labor.
The construction of the beds is
nearly as simple as their operation, only
common labor being required, except
putting down pipe and accessories.
The
for
essential features of filter beds are
some 4 to 5 feet of medium-sized sand,
located above the natural ground water
level; a pipe system for distributing the
sewage to one or more points on each bed,
and another beneath the bed, for collecting
the purified liquid. In operation, the sewage is turned on to one bed for a given
length of time, and then to another, in
order to give the first a rest, or literally a
breathing spell. When the beds become
clogged with the matter retained on their
surface and in their uppermost part, they
may be raked over, or the sludge, and with
it a thin layer of sand, may be scraped off.
133
If the beds are scraped, it will eventually
be necessary to make good the sand re-
moved, although
this will not
be required
until perhaps a foot has been taken off,
which should not result for a long time.
Intermittent filtration is a nitrifying
process effected through the agency of oxygen and bacteria, and requiring time for
these
two
factors to act.
A more complete
perhaps that given in the
Massachusetts State Board
of
the
Report
of Health for 1893, as follows:
definition
is
The process * * * consists of intermingling
the sewage in the pores of the filtering material,
with sufficient air for a sufficient time, in the presence of micro-organisms which quickly establish
themselves there.
Experience has taught that a good filtering material is one composed of clean,
sharp sand with grains of uniform size,
and having interstices forming about onethird the total volume.
The
interstices
serve as air spaces. When the sewage is
admitted to the sand not all the air is
driven out, and hence thtre
is
a store of
oxygen to be drawn upon by the bacteria*
134
As more and more sewage
is
added the
exhausted, the nitrifying bacoxygen
teria diminish in numbers, as they cannot
is
live
without
air,
and the
efficiency of the
purification process diminishes. If the application of sewage ceases, the beds grad-
ually
become drained as the sewage goes
air is drawn into the pores of the
down,
bed, until finally a
new supply
is
secured
and the operation can be repeated. The
sewage in filter beds spreads itself in thin
films over the sand grains, thus giving
bacteria an opportunity to develop, feed
upon the organic matter, and so break it
up as to cause the formation of new compounds, until the organic matter
is
trans-
formed into inorganic.
If intermittent filtration
were a mere
straining process, then the finer the sand
used the higher the degree of purification.
As already pointed
out, it is a nitrifying
rather than a straining process, so the aim
must be to select a material of the size best
suited to that end, and which will
same time give the highest rate of
at the
filtra-
tion with the least expenditure of labor.
135
The
luw rate of filand a high degree of purity. The
sewage not only enters the sand slowly,
finer materials give a
tration
but a long time
is
required to drain
it
out
and renew the air. If crowded, poor reWith
sults and ultimate clogging follow.
coarse material the sewage passes through
too rapidly for nitrification to take place.
The drainage and air renewal can therefore
be effected quickly. It
is
thus evident that
with very fine material the sewage must
be applied slowly, with long intervals of
rest,
while with very coarse material the
rate of application must be yet slower and
the rests far more frequent, though short.
As compared with material of a medium
the fine does not give sufficiently better results, in actual practice, to warrant
its adoption, nor does the higher rate possize,
sible
with the coarse material.
The slow
and the tendency to clog,
on the one hand, and the very frequent
manipulation of gates to throw the beds
into and out of use, on the other, are
rate of filtration
against the extremes. Moreover, the very
coarse materials are not so certain in their
136
removal of bacteria as fine ones. Here, as
elsewhere, a happy mean is to be sought.
R( jecting the extremes, the Massachusetts
State Board of Health, in its report for
1891, gives as the range of available masand having 10 percent, of its weight
terial
finer than 0.03 to 0.98
millinuUTS (0.0012 to 0.0392 ins.).
All material in filter sands finer than
composed of grains
O.C1
mm.
matter.
(O.C004
ins.) is classed as
The maximum
size of
organic
the coarser
materials included in the above range was
about 0.5 in. in diameter, and the mini-
mum size of the finest material was
0.01 in.
in diameter.
As the work done by a filter is largely
determined by smalltr particles of sand,
and as a sand of uniform size is desired, the
Massachusetts State Board of Health has
adopted two standards for comparing different materials. The sand is subjected to
mechanical analysis to determine the per-
by weight, of the total which
have grains below a certain diameter. The
diameter at the 10 per cent, point is taken
as the effective size, and the uniformity
centages,
137
coefficient is the ratio
between the diameter
of the grains at the 60 and 10 per cent,
points.
Although a range
sand
in the size of the
may be allowed, the coarse and
finer particles should be fairly well intermingled. Or, in other words, there should
not be strata of fine and coarse material in
grains
a
filter
The
bed.
effect of stratification is
well expressed in the report of the MaspaQhusetts State Board of Health for 1892,
as follows:
We have thus found that with a coarse material
above a fine one in the same filter thsre is a chance
of trouble from a clogging of tlio fine material below the coarse
;
and
this is far
wo.se than surface
clogging, for the latter can be completely remedied
have
by disturbing the surface or by scraping.
We
found that a fine sand supported by a coarse
sand will keep its lower layer saturated and act as a
also
water
allowing the passage of water, but not
and may in this way prevent tha necessary
circulation of air, and reduce the action of the filter
to mere straining.
of
seal,
air,
*******
*
The above examples are perhaps extreme cases.
With less marked differences in sand sizes, or with
gradual instead of abrupt transitions from ccarse
138
to fine, the causes of failure might be reduced, or
even in some cases entirely eliminated. In the
many cases where the fields available for sewage
filtration
contain layers of various materials, the
must be separately studied, in order
different sands
to detormine the probabla action of existing combinations; and in case the natural conditiors are
unfavorable, changes may be made which will improve the action of the filter.
Not
all communities are so fortunate as
have ideal filtering material conveniently located for sand filter beds. If net,
then the choice may be between extending
the outfall sewer to a distance, with or
without pumping, and the adoption of a
site giving poor material and thus requiring a larger area, or an inferior sand may
be the only kind available far or near.
The Lawrence experiments, to which reference has freely been made, have now
been carried on for about seventeen years,
to
and the
results of fifteen years' studies of
a great variety of material under widely
different conditions are on record in the
published reports of the Massachusetts
State Board of Health. Actual results obtained at city
filter
beds are also available,
139
so that with expert advice any community
may ascertain the approximate possibilities
While
and gravels may be
good results, under
of such materials as are at hand.
a wide range of sands
counted on for giving
proper conditions, it is necessary to determine those conditions in order to know
to provide, and how to
the
after
the disposal grounds
sewage
apply
are ready. The area and volume of sand
what area of beds
or
gravel required for the intermittent
sewage are so large that the
transportation of material any great disfiltration of
is out of the question.
Generally
speaking, the beds are constructed in ma-
tance
and
loam of course being removed, together
with any pockets of other unsuitable material as naturally deposited, top soil
terial.
The sewage is carried to the several beds
through open or closed channels built in
the embankments, with distributing chambers where two or more beds join together.
Ordinary sewer pipe, half pipe, brick, concrete or even wood conduits may be used.
The distributing chambers may be of any
140
of the above materials, excepting sewer
Wood
of masonry.
pipe, but are generally
are
to be avoided, if
or
accessories
carriers
on account of becoming sewageand
thus liable to give off bad
soaked,
possible,
odors.
The sewage should be brought onto the
beds so as to disturb their surface as little
as possible, and great pains should be taken
to distribute it evenly over the whole bed.
The underdrains should
rarely, if ever,
be placed more than 50 feet apart, and
should be provided with manholes, or
inspection chambers at all intersections.
Underdrains are sometimes put much
nearer together than this. Their size and
depth will be governed by the amount of
effluent they are expected to remove, the
ground water level and possibly other local
conditions.
Before admitting sewage to the beds
it
generally advisable to screen it, at least
sufficiently to take out paper, rags and
large floating matter. The screening cham-
is
bers often serve to
some extent as
settling
size to
tanks, but must be of pretty large
141
remove any considerable proportion
of the
total matters in suspension.
Crops are
beds, which
sometimes
is
raised on filter
equivalent
to practicing
broad irrigation in summer and filtration
the remainder of the year. The beds generally being thoroughly underdrained, and
the soil often more permeable than that of
a broad irrigation area, larger doses of
sewage may probably be applied to crops
on filter beds than those growing on ordinary sewage farms.
The size of each bed should be such as
to permit an easy and equable distribution
of sewage over it. Where the total filtration area is small it must be divided so as
to permit of intermittent operation; that
is, if a bed is to be in use and at rest for
equal periods, then at least two beds would
be necessary, and so on according to the
relative periods of use
and
rest.
Some
additional area should also be provided
for use while beds are being scraped or in
case of an emergency.
If a large area is
laid out so that the size of the beds is lim-
142
ited only by convenience in use, then an
acre may be a very acceptable size.
As to degree of purification which may
be expected, and the rate of filtration, it
may be said, without going into details,
that practically all of the organic matter
may be removed from sewage by intermittent filtration at rates approximating
100,000 gallons per acre per day, with the
best material and all conditions favorable.
With unfavorable
conditions the rate
may
be as low as 30,000 gallons per acre per
day or even less.
CONTACT BEDS.
To make possible an increase in the low
rates feasible with intermittent filtration
under even the best conditions, and also to
lessen the clogging of such beds (the two
efforts being largely identical), the Massachusetts State Board of Health early began
to experiment with various preliminary
processes of sewage treatment, including
rapid filtration of various sorts and sedi-
mentation.
A little
later
than these exper-
143
iments, and in
some instances coincident
with them, a number of men began experiments on their own account. These included the late Colonel George E. Waring
in America, and Scott-Moncrieff, Dibdin
and others in Great Britain. In the latter
country intermittent filtration has almost
always been supplemental to broad irrigation or
sewage farming.
The clayey na-
ture of most of the available land
density of population,
and the
made imperative
some change in sewage treatment in Great
Britain, and from about 1892 on gave rise
to a multiplicity of new schemes.
Except
for details these schemes may be narrowed
down
ters,
to contact beds
and percolating
fil-
with the septic tank, which has been
described already, available as preliminary
to either of these, and also to broad irrigation and sewage farming.
Although, as a
rule, it is
dangerous to credit these newer
processes to a single man, the contact bed
may be ascribed to W. J. Dibdin, for some
years Chemist to the
cil.
The
London County Coun-
percolating
filter,
as described in
subsequent pages, cannot be so readily
144
credited to a single individual, since the
Massachusetts State Board of Health, Col-
onel Waring, Scott Honor off and several
others had a hand in its development.
i
Both the contact bed and the percolating
filter, in their working form and the extent
of their use, are essentially British. It
may also be stated here that the septic
tank was combined with contact beds almost if not quite from the beginning of
the development of the former by Donald
Cameron.
The contact bed
differs
can type of intermittent
composed of
much
erally enclosed
floor,
by
from the Amerifilter
in being
coarser material, genwater-tight walls and
the basin thus formed being pro-
vided with inlet and outlet gates. It also
differs from the intermittent filter in that
when
in use the outlet gates are closed,
the bed filled quickly and held full for two
hours or so, then emptied quickly and kept
empty for two to four or five hours. The
series of operations is called a cycle, and
there are from two to four cycles in each
24.hours. The filling and emptying gates
145
are frequently worked automatically
means of specially designed apparatus.
Contact beds are
singly, in
by
built -for operation
pairs and in groups of three;
the sewage in the last two cases passing
through two or three beds in succession.
When
built in pairs a coarse and a fine
bed are provided. The coarse material is
approximately from 3-4 to 2 ins. in greatest diameter, and the fine material from
1-4 to 1 in. The material now most commonly used in contact beds abroad is hard
clinker from soft coal or from refuse destructors, but coke, broken stone a gravel
and other substances may be employed.
Care should be taken to select a material
which does not readily disintegrate. The
coarse beds are sometimes called primary,
and the fine ones secondary, and sometimes
the terms single and double contact beds
are used.
The
relatively large size of the material
composing these beds, and of the intersti-
permits quick filling and empfacilitates also a rapid renewal
of the air supply in the free spaces or pores
tial spaces,
tying, and
146
The latter, in turn, favors an
enormous bacterial development and a corlespondingly speedy breaking down and
of the bed.
transformation of the organic matter of
the sewage. As can be understood, holding the sewage in the bed in contact with
the bacterial agents gives the beds their
name.
Some form of preliminary treatment,
most commonly septic or sedimentation
tanks, has been found advisable before
applying sewage to contact beds, particularly where only a single contact is pro-
A high
degree of bacterial removal
commonly effected by contact beds,
unless very fine material is employed, but
vided.
is
not
the organic matter in the sewage may nevertheless be so transformed as to prevent
from subsequent putrefaction,
usually the main object of sewage
treatment. With such an object it is renuisance
which
is
ported that satisfactory results have been
obtained when passing settled or septic
sewage through double contact beds at
from 500,000 to ], 000,000 gallons
an acre of total surface area.
rates of
147
PERCOLATING FILTERS.
Trickling,
continuous
streaming and intermittent
filters
are
some of the names
that have been applied to the last class of
awaiting consideration, but both
reason and usage are on the side of the
filters
term percolating
The
filters.
features of percolating
are the use of large-sized material,
with the freest possible aeration and drainessential
filters
age, and a uniform distribution of the
sewage over the filter in drops, small
streams or spray.
The sewage has an un-
interrupted passage through the drainage
system of percolating filters, just as through
intermittent
filters,
but tLe sewage
is
ap-
plied continuously, or with numerous brief
interruptions that break the continuity but
a
little,
in the case of percolating filters,
and the distribution is so even and rapid,
and the pores of the filters are so large,
that no sewage stands oa the percolating
whereas the surface of intermittent
often flooded hours at a time.
Percolating filters are generally built on
filters,
filters is
148
a solid
floor of concrete or other water-
tight material, and enclosed by openjointed walls, the latter consisting of large
fragments of the medium, laid up with
joints, or regular sized moulded or
cut pieces, laid pigeon-hole fashion. Tne
body of percolating filters is composed of
open
clinker, stone or other fairly cohesive
terial, in particles
egg or a man's
from the
fist
up
ma-
size of a hen's
to that of a man's
head, the larger pieces being placed at the
bottom.
Distributors for percolating
filters
may
be revolving radial arms of wrought-iron
pipe, perforated, or revolving radial weirs,
or fixed pipes provided with mere perforations or with spray nozzles. Drains, formed
in the concrete or other solid floor, or con-
sisting of specially moulded tiles, are used
to ensure thorough drainage.
The effluent from percolating filters,
even when the original sewage
is
given a
usually high in
preliminary treatment,
divided
suspended matter, and also
finely
in bacteria, but, as a rule, the effluent is
is
non-putrefactive and, being largely min-
149
eral matter, is easily removed or reduced
in quantity by a brief period of sedimenThe rates claimed for percolating
tation.
filters,
dosed with septic sewage,
range
from 1,000,000 to 10,000,000 gallons an
but in the present state of the art
2,000,000 to 3,000,000 gallons seems high.
acre,
SEWAGE
PLANTS
PURIFICATION
NOT
NUISANCES.
There
much
opposition to sewage purification plants by those living or
owning property near by on the ground
is
often
that such works must of necessity be a
From experience gained by
nuisance.
visiting
many
such plants, both in this
country and abroad, and from studying
the subject in other ways for years, I know
that well conducted plants are entirely inoffensive, either within
The
or without their
employees about such
works are as healthy as similar classes
of
men in other occupations, and
the same holds true of the families of these
men living on the European sewage farms.
enclosures.
150
The
crops raised on sewage farms are as
safe eating as those of the same kind raised elsewhere. There are objections, however, to applying
sewage to crops for hu-
man consumption which
are to be eaten
without being cooked, but meat and milk
from sewage farms is usually as good as
when produced under other conditions.
Good design and construction, followed
by proper methods of operation, are all
make sewage purifica-
that are needed to
when once the right system
has been adopted and put into use. No
one system can be said to be the best for
tion a success,
The special problems of
all localities.
each community must be met and solved
case by case and out of several systems
and combinations of systems the best for
the conditions at hand must be chosen.
THE PRESENT STATUS or SEWAGE
PURIFICATION.
In the United States, chemical precipitation is no longer being adopted for new
The septic tank has come more
plants.
rapidly into favor than contact beds or
151
filters, but some men of pracexperience seem strongly inclined to
plain sedimentation rather than the septic
percolating
tical
tank.
Comparatively few percolating filbuilt, but small contact
Uis have been
beds are in use in a number of cases.
In-
termittent filtration has for years been the
system most in use in America, and seems
likely to continue to lead
for filter beds
is
where sandy land
available at a reasonable
In our Far West, sewage irrigation
price.
frequently practiced, but as a rule the
sewage is merely a substitute for water in
is
sections
where
irrigation is a necessity.
be the most successful
to
appears
farm
in
the
United States treats
sewage
What
the sewage of Pasadena, Cal. Large and
paying crops of walnuts are raised each
year.
farm
On
in
a visit to the Pasadena sewage
March, 1905, the author was told
number of orange trees would
be set out soon, and that sewage would be
put on these in the summer and on the
that a large
walnut trees in the winter.
Early in 1904 the author visited twentyfour sewage works in Great Britain and
152
three on the continent of
Europe.
lie
numerous chemical precipitation
plants and sewage farms still in use, at
the works visited and elsewhere, but many
of these were being converted to, or supplemented by, the newer processes. The
septic tank was widely used. Contact beds
were numerous and percolating filters were
found
fast
becoming
so.
In America the septic tank, contact beds
and percolating filters are far less often
compared with other processes, than
Great Britain. Local conditions abroad,
should be remembered, are widely dif-
used,
in
it
ferent
from
local
conditions here.
The
streams of Great Britain are small and the
population dense, requiring more sewage
works than are yet felt to be necessary in
the United States, and the clayey soil and
good natural filtering maEngland and Scotland compels
the adoption of clinker, coke and other
absence of
terial
in
substitutes.
All these things should be
remembered in selecting a mode of treatment and filter bed material for American
sewage works.
153
If it
seem
to
any that the newer pro-
sewage treatment have been but
briefly discussed, the author would point
out the fact that in 1904 there was pubcesses of
lished a
tled,
whole volume in
this series, enti-
" The Treatment of
Septic Sewage,"
by George
W.
Rafter,
M. Am.
Soc. C. E.
Later in 1904, the author of the book
now
being brought to a close, embodied his recent observations in Great Britain and at
in " BritFrankfort and
Wiesbaden,
Paris,
Sewage Works." Present day sewage
treatment, from the viewpoint of British
" The
authorities, is set forth in Barwise's
ish
Purification of Sewage," Rideal's " Sewage
and the Bacterial Purification of Sewage,"
and Dibdin's "The Purification of Sewage
and Water." The first American book on
"
sewage was Rafter and Baker's Sewage
in
the
United
States," a large
Disposal
treatise on the subject published early in
1894, before the septic tank, contact beds
and percolating filters had come into public
view.
A
revision
under consideration.
of this treatise
is
THE VAN NOSTRAND SCIENCE SERIES
No. 47.
LINKAGES: THE DIFFERENT FORMS
and Uses
No. 48.
By
of Articulated Links.
J.
D. C.
De
Roos.
THEORY OF SOLID AND BRACED
Elastic Arches.
tion, revised
By William
Second edi-
Cain, C.E.
and enlarged.
No. 49. MOTION OF A SOLID IN A FLUID. By
Thomas Craig, Ph.D.
No. 50. DWELLING-HOUSES; THEIR SANIBy Prof. W. H.
tary Conduction and Arrangements.
Corfield.
No. 51.
THE TELESCOPE: OPTICAL PRINCI-
ples Involved in the Construction of Refracting
and
Telescopes, with a new chapter on the
Evolution of the Modern Telescope, and a Bibliography
With diagrams and folding plates. By
to date.
Thomas Nolan. Second edition, revised and enlarged.
Reflecting
No. 52.
IMAGINARY QUANTITIES;
Geometrical
Interpretation.
No. 53.
How
No. 54.
INDUCTION COILS;
Used.
S.
HOW MADE AND
KINEMATICS OF MACHINERY. By
With an
of
Second
edition, revised
and
THE ACTUAL LATERAL PRESSURE
Earthwork.
No. 57.
Introduction by
SEWER GASES; THEIR NATURE AND
Origin.
By A. de Varona.
enlarged.
*No. 56.
the
Hardy.
Eleventh American edition.
Prof. Alex. B. W. Kennedy.
Prof. R. H. Thurston.
No. 55.
THEIR
from
Translated
French of M. Argand by Prof. A.
By
Benj. Baker,
M.
Inst.,
C.E.
INCANDESCENT ELECTRIC LIGHT-
A Practical Description of the Edison System.
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by John W. Howell.
ing.
No. 58. VENTILATION OF COAL MINES. By
W. Fairley, M.E., and Geo. J. Andre.
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With Comments. By S. W. Robinson, C.E.
OF WROUGHT-IRON
No. 60. STRENGTH
Bridge Members. By S. W. Robinson, C.E.
No. 61. POTABLE WATER, AND METHODS OF
Detecting Impurities. By M. N. Baker. Second edition, revised
No. 62.
and enlarged.
THEORY OF THE GAS-ENGINE.
Dougald
matter.
Third
Clerk.
edition.
With
Edited by F. E. Well, M.E.
By
additional
THE VAN NOSTRAND SCIENCE SERIES
HOUSE-DRAINAGE AND SANITARY
No. 63.
Plumbing.
By W.
P. Gerhard.
Twelfth edition.
ELECTROMAGNETS. By
No. 64.
A. N.
Mans-
Second edition, revised.
field.
POCKET LOGARITHMS TO FOUR
No. 65.
Places of Decimals.
Including Logarithms of
Num-
bers, etc.
DYNAMO-ELECTRIC MACHINERY. By
No. 66.
S. P.
Thompson.
With an Introduction by
F. L. Pope.
Third edition, revised.
HYDRAULIC TABLES FOR THE CAL-
No. 67.
culation of the Discharge through Sewers, Pipes, and
Conduits. Based on "Kutter's Formula." By P. J.
Flynn.
STEAM-HEATING.
No. 68.
By Robert Br
Third edition, revised, with additions by A. R.
Fifth edition, revised
Foye.
No.
70.
W
CHEMICAL PROBLEMS. By Prof. J.
No. 69.
EXPLOSIVE
C.
and enlarged.
MATERIALS.
By
Lieut.
John P. Wisser.
No.
No.
DYNAMIC ELECTRICITY. By John
J. N. Shoolbred, and R. E. Day.
TOPOGRAPHICAL SURVEYING. By
71.
Hopkinson,
72.
George
and H.
Specht, Prof. A. S. Hardy,' John B. McMaster,
Fourth edition, revised.
F. Walling.
J.
SYMBOLIC ALGEBRA
TESTING MACHINES;
THE
ALGE73.
;
OR,
bra of Algebraic Numbers. By Prof. William Cain.
HIS74.
By Arthur V. Abbott.
tory, Construction and Use.
IN
No. 75.
electric Machines.
Being a Supplement to "Dynamoelectric Machinery.
By Prof. Sylvanus P. Thompson.
No. 76.
Processes.
By Lieut. James S. Pettit, U.S.A.
No. 77. STADIA SURVEYING. The Theory of
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By Arthur Winslow. Eighth
No.
No.
RECENT PROGRESS
THEIR
DYNAMO-
MODERN REPRODUCTIVE GRAPHIC
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THE STEAM - ENGINE INDICATOR
By W. B. Le Van.
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FOR
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COMPARATIVE
*No. 81. WATER METERS:
No.
78.
and
No.
Its Use.
79.
Tests of Accuracy, Delivery, etc.
of the Worthington, Kennedy,
meters.
By Ross E. Browne.
Distinctive Features
Siemens,
and Hesse
THE VAN NOSTRAND SCIENCE SERIES
No. 82.
THE PRESERVATION OF TIMBER BY
the Use of Antiseptics.
By Samuel
Bagster Boulton,
C.E.
MECHANICAL INTEGRATORS.
No. 83.
Prof.
No. 84.
Henry
OPEN CHAN-
IN
With Tables.
nels, Pipes, Conduits, Sewers, etc.
P. J. Flynn, C.E.
No. 85.
Prof.
No. 86.
De Volson
HANDBOOK OF MINERALOGY; DEand Classification of Minerals
By
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J.
C.
Foye.
TREATISE ON THE THEORY OF THE
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L. Culley, C.E.
*No. 88.
By
THE LUMINIFEROUS AETHER. By
Wood.
termination, Description,
Found in the United States.
Fifth edition, revised.
No. 87.
By
H. Shaw, C.E.
S.
FLOW OF WATER
By John
BEAMS AND GIRDERS. Practical Forfor their Resistance.
By P. H. Philbrick.
MODERN GUN COTTON: ITS MANU-
mulas
No. 89.
facturo, Properties,
and Analyses.
By
Lieut.
John P.
Wisser, U.S.A.
No. 90.
ROTARY MOTION AS APPLD3D TO
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No. 91.
No. 92.
Use.
No. 93.
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J.
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LEVELING: BAROMETRIC, TRIGONO-
metric,
edition.
and
Spirit.
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Prof.
I.
O.
Baker.
Third
PETROLEUM; ITS PRODUCTION AND
By Boverton Redwood, F.I.C., F.C.S.
RECENT PRACTICE IN THE SANI-
With Memoranda on the
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By William Paul Gerhard, C.E.
OF SEWAGE. By
No. 94.
tary Drainage of Buildings.
THE TREATMENT
Meymott Tidy.
No. 95. PLATE-GmDER CONSTRUCTION. By
Isami Hiroi, C.E. Fourth edition, revised.
No. 96. ALTERNATE-CURRENT MACHINERY.
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DISPOSAL OF HOUSEHOLD
No. 97. THE
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No. 98. PRACTICAL
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Engine
with notes, etc., by F. E. Idell, M.E.
DYNAMO-BLTLDING FOR
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THE
No. 101.
SEXTANT, and Other
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Mathematical Instruments.
Adjustment and Use.
Navy.
By
their
F. R. Brainard, U. S.
THE GALVANIC CIRCUIT INVESTI-
No. 102.
gated Mathematically. By Dr. G. S.
1827.
Translated by William Francis.
and
Notes by the Editor,
M.I.E.E. Second edition.
Potable
Rafter.
Water.
Second
With
Diagrams.
By
Geo.
W.
edition.
VAN NOSTRAND'S TABLE-BOOK FOR
No. 104.
and Mechanical Engineers.
Civil
Geo.
Berlin,
With Preface
THE MICROSCOPICAL EXAMINATION
No. 103.
of
Ohm,
Thomas D. Lockwood.
Compiled by Prof.
W. Plympton.
DETERMINANTS. An
No. 105.
Introduction to
the Study of, with Examples and Applications.
Prof. G. A. 'Miller.
COMPRESSED
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AIR.
By
Experiments upon
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By Prof. A. B. W.- Kennedy. The
(Popp's System.)
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By Prof. W. C. Unwin.
Edited by F. E. Idell. Third edition.
A GRAPHICAL
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A Rational and Easy Graphical Analysis of
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With an Introthe Stresses in Ordinary Swing Bridges.
duction on the General Theory of Graphical Statics, with
F. La
Second
edition.
Plates.
Benjamin
By
Folding
Rue.
No. 108. SLIDE-VALVE DIAGRAMS. A French
Method for Constructing Slide-valve Diagrams. By
Bankson, B.S., Assistant
8 Folding Plates.
Lloyd
Naval Constructor,
U. S. Navy.
No. 109.
THE MEASUREMENT OF ELECTRIC
Instruments.
Electrical
Currents.
Measuring
By
James Swinburne. Meters for Electrical Energy. By
Edited, with Preface, by T. ComC. H. Wordingham.
merford Martin. With Folding Plate and Numerous
Illustrations.
No. 11O.
TRANSITION CURVES.
for Engineers, Containing Rules
out
Transition
Second
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Curves.
A
Field-book
and Tables
By Walter G.
for
Laying
C.E.
Fox,
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GAS-LIGHTING AND GAS-FITTING.
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Advantages
and Rules for Gas-piping. Notes on the
Gas for. Cooking and Heating, and
Gas Consumers. Third edition. By
of
Useful Hints to
Wm.
Paul Gerhard, C.E.
No. 112.
ON THE CALCULUS.
A PRIMER
E. Sherman Gould, M.
revised and enlarged.
No. 113.
Am.
Soc. C.E.
PHYSICAL PROBLEMS and
By A. Bourgougnon, formerly
Bellevue Hospital. Second edition.
lution.
No. 114.
USE
OF
THE
SLIDE
Their SoAssistant
RULE.
F. A. Halsey, of the "American Machinist."
edition, revised and enlarged.
No. 115.
TRAVERSE TABLE.
By
Third edition,
at
By
Fourth
Showing the Dif-
ference of Latitude and Departure for Distances Between
1 and 100 and for Angles to Quarter Degrees Between 1
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Pocket Table Book.)
No. 116.
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AND SPIRAL GEARING.
WORM
from "American Machinist."
F. A.
By
printed
Second revised and enlarged
No. 117.
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Re-
Halsey.
edition.
HYDROSTATICS,
AND
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Gould.
No. 118.
TREATMENT OF SEPTIC SEWAGE,
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Rafter. Second
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No. 121.
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Reprint of a Set of Notes accompanying a Course
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By
Sanford A. Moss. Illustrated.
No. 122.
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Illustrated.
FURNACE DRAFT ITS PRODUCTION
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