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Cornell University Library
TD 778.U58

Concrete septic tanks for farmhouses and
3 1924 003 640 681

[concrete Septic Tanks

For Farmhouses and Dwellings

Small ToNA/ns

Prepared and published by

Universal Portland Cement Co.

Chicago — Pittsburgh — Minneapolis — Duluth

CONCRETE SEPTIC TANKS

Concrete Septic Tanks for Farmhouses and
Dwellings in Small Towns

Most persons will be surprised to know that recent statistics show
many cities are far healthier places in which to live than is the average
rural community. The reason for this is that city health authorities
enforce regulations compelling the disposal of house wastes in a sanitary
manner. Most cities are equipped with sewage systems, and disposal
plants where sewage is rendered practically harmless. Small towns
and rural communities are not usually so favored. Farmhouse wastes
are often thrown out upon the ground in a thoughtless manner, with-
out regard for the possible sickness and death that may result from
such practice, not only to persons in the immediate locality, but to others
far away. Most epidemics of disease in the city, such as typhoid, scarlet
fever and diphtheria, can generally be traced to insanitary conditions on
the farm — contaminated water supplied to dairy stock.

Experiments have proved that disease germs have lived through a
trip of 90 miles in river water. The New York State Board of Health
reports an instance where ignorance on the part of a backwoodsman who
was ill from typhoid fever, was the direct and only possible cause of a
typhoid epidemic in Plymouth, Pennsylvania, in which more than 1,000
persons were affected and more than 100 died.

Many disease germs are not easily made harmless or destroyed by
methods that the average farmer usually adopts for disposing of house-
hold wastes. Typhoid germs buried in cultivated soil will possibly be
found alive and dangerous three to six months after the time they were
so scattered. Other experiments have proved that typhoid germs are
not destroyed by the action of rotting bacteria in a cesspool.

House wastes scattered upon the ground or even discharged into a
cesspool, seep thru loose soil and eventually contaminate water supply
which, in turn, passes germs on to dairy stock, then into milk. Cesspools,
if located in firm soils, must be pumped out periodically. In such cases
the contents are distributed over the surface of the ground, giving forth
vile odors, and the filthy wastes are sooner or later washed into some
stream, thus polluting it and spreading infection. If the cesspool is
located in sandy or gravelly soil through which the contents may con-
tinually seep out, then sooner or later the source of domestic water supply
on the farm — the well — will become contaminated.

Modern conveniences of the city dwelling have been extensively
adopted for the farmhouse. The kitchen sink, the bath and indoor toilet
are too convenient to do without, yet have a penalty attached unless the
wastes that are handled by such a system of house plumbing are disposed
of in a satisfactory manner. The cesspool should no longer be tolerated.
Instead, a sewage disposal system that will be sanitary, convenient for
use, easy to maintain and of simple construction, should be substituted.
Such a system is represented in the modern septic tank which provides
for final disposal of house wastes thru either of two methods that will
be described more fully later.

A properly designed septic tank makes use of the process or agenci( jg
of Nature. Such a tank should have not fewer than two compartment

Copyriehi— 19) 5— Universal Pohtland Cement Co.— 10M-9-10-1S-D

UNIVERSAL PORTLAND CEMENT CO.

House sewage is discharged into the first of these compartments (some-
times called the sedimentation chamber) where bacteria develop, multiply,
and feed on the sewage, so to speak, thus breaking up and changing a
portion into relatively harmless compounds. Such processes as occur
in this first compartment, however, do not render the sewage entirely
harmless. The bacterial process occurring in the first compartment, which
must be dark and practically airtight, represents one of two successive
stages necessary for sewage purification. The second, which consists of
a combination of oxidization, nitrification and filtration, must be performed
in the presence of light or air, or both. The order of purification must
always be as just indicated, first, the bacterial action; second, aeration
and nitrification — never the reverse.

Final disposal may be carried on in either of two ways. Where
possible to do so, surface, or broad irrigation is satisfactory, which means
discharging the sewage from the septic tank upon the land, where it is
allowed to spread over the ground and be acted upon by the sun and certain
other bacteria which live in the upper layers or portions of the soil. The
plot of ground used for this purpose may be cultivated land or may be an
area of waste land. In either case it should be located as far as possible
from the source of domestic water supply, this distance never being less
than 200 feet. Care should be taken to keep dairy cattle from grazing
over the disposal area.

Discharges from the tank should be carried to the disposal field by
a tile line having sealed joints and emptying into an open ditch about
12 inches wide and 6 inches deep, with laterals at right angles to it and
about 6 feet apart, dug with sufficient grade so that the liquids will spread
quickly and evenly over the whole area.

Another method of disposal is frequently practiced. This is called
sub-surface irrigation, and consists of discharging the tank contents into
lines of 4-inch drain tile laid with open joints from which the fiuids leach

/4' Open Jointed Tile

A'Sewer

4'Main,

R-

Septic Chamber \
5'5iphon^

Tile - Closed Joints

f4"Open Jointed Tile

gi-o'—^

'^" Length varieble depending on character -A
I of soil \

-^ SUB - IRRIGATION SYSTEM ^-

Figure 1. Plan of Septic Tank with Final Disposal System After the Sub-irrigation Method,
showing also a section of trench which may sometimes be necessary when tile are laid in tight soil

CONCRETE SEPTIC TANKS

or filter into the soil. The grade of such a tile line should be not greater
than 2 or 3 inches per hundred feet.

To prevent soil from entering the tile line through the open joints,
these may be covered with flat stones or pieces of broken tile of larger
diameter.

Sub-surface irrigation is in a way similar to broad irrigation, in that
the final stage is filtration; the intermediate step, namely, aeration and
nitrification, being carried on immediately beneath the surface of the
ground instead of on its surface.

Figure 1 illustrates the disposal method by sub-irrigation. Length
of drains necessary will be governed by the nature of the soil. If this is
loose and sandy, 200 feet is suflBcient, although in tight soil it may be
necessary to double this length.

Generally speaking, the method of disposal by sub-surface irrigation
is best adapted to the single residence. This system usually requires less
attention to secure satisfactory operation; furthermore, the sewage is

Co\/er

Figure 2. Septic Tank for Use Where Sub-irrigation is Practiced, showing
tank interior partly exposed as if a portion of the tanlc were cut away.

entirely hidden from sight after discharged from the tank, and this is a
desirable feature.

Sub-surface irrigation is not well adapted to firm or dense soils. In
such cases a plan sometimes adopted is illustrated at "A" (Figure 1);
that is, the tile are laid on a gravel or cinder filling in trenches, then cov-
ered with about a foot of earth. In heavy clay soils an additional line of
tile in the lower portion of trench to drain it is frequently necessary.

The design in Figures 2 and 3, shows a septic tank as it would appear
if partly cut away to expose the interior to view, and as if cut in half along
a center line following its length. This type will be found to operate

UNIVERSAL PORTLAND CEMENT CO.

effectively where final disposal is accomplished by sub-surface irrigation.
This system once started is self-operating due to the siphon* shown in
the second, or right-hand compartment, which at regular intervals
empties the contents and discharges them into the line of tile from
which the liquids leach out thru joints into the soil. In a tank con-
structed as shown in the design mentioned, it is very important to use a
siphon to empty the second compartment at intervals instead of allowing
a continuous outward flow of contents, because of the tendency for drains
to become clogged when liquids are constantly trickling through.

The size of tank required for residence use depends upon the quantity
of sewage to be handled in the first chamber during a day of 24 hours,
therefore, this compartment should be large enough to contain an entire
day's fiow. This frequently amounts to from 30 to 50 gallons per person
per day, so the required capacity can readily be computed from these
figures, although it must be remembered that the required depth for the
tank should be figured from the top of the concrete bafHe wall or partition

No. 9 Wtre 6'c to c. or Z'mssh poultry
netting i' from txiffom,

f f aUrt' A

f Round rods-
ffctoct'ebo/e
bottom of stab'

^timtin

Rpe Inlet-

/Round I
radsf-C^ctocr'

Figure 3. Septic Tank Same as Shown in Figure 2. This shows the construction as if cut away
alone a center line following its length, also a section of the siphon chamber and a plan of the
^vhole construction.

which separates the first and second compartments. Another point to
bear in mind is that the width of the first compartment should be about
one-half its length.

*Such siphons are not expensive and can be obtained from any one of the following
concerns:

Pacific Flush Tank Co., Chicago.

Merritt & Co., Philadelphia.

The Hendire & Bolthoff Mfg. & Supply Co., Denver.

S. Story & Sons, Cedar Rapids, Iowa.

CONCRETE SEPTIC TANKS

Where broad irrigation is practiced because of dense soil or where the
fall of ground does not make the sub-surface irrigation system practicable,
then the design shown in Figures 4 and 5 will be found effective. If the
length of first chamber is 3 feet 9 inches, the tank will accommodate the
wastes from a household of 6 persons, figuring that an average of 50 gallons
of sewage per day for each member must be disposed of. If a family of
8 is to be served, the length "A" should be made 5 feet. It is estimated
that one day will be required for a given amount of liquid to pass thru
the first compartment, under the baffle and over the weir or partition wall,
upon the sand filter.

In both of the designs presented, it will be noticed that baffle boards
are shown. These are for the purpose of preventing any disturbance of
the scum which forms on the surface of the liquid in the first compartment,
because efficient bacterial action is dependent upon keeping this scum
motionless and preventing any of it from being carried out of the com-
partment. These baffles break up eddies and currents caused by the flow
coming into the tank and in the first design consist of two 2 by 18-inch
boards set in slots formed in the tank walls at the time concrete is placed.

In the second design concrete baffles are shown, as well as three
1 by 6-inch boards so placed at the inlet side of the first compartment that
they will break currents from sewage entering the tank. These boards
are secured in position by toenailing at the ends to small pieces of lumber
set into the tank walls when concrete is placed. Both designs show
manholes which permit access to the tanks for cleaning, tho the necessity
for this is infrequent.

Septic tanks are best constructed of concrete, which should be mixed
in the proportions of 1 sack of Portland cement to 2 cubic feet of coarse
sand graded up to J^ inch, to 3 cubic feet of screened gravel or crushed
stone, the particles of which vary in size from J^ to Ij^ inches. Enough
water should be used to produce a mixture of quaky consistency so that
the concrete when placed will settle into all parts of the forms when
slightly jogged or puddled with a spade or similar tool. Spading assists

Baff/es

Inlet

Reinforcing

Figure 4. Septic Tank of a Type Adapted for Use Where Final Disposal is Made by Means oi
Broad Irrigation. This view shows the construction as though partly cut away to expose the
interior view.

•tlllllll

UNIVERSAL PORTLAND CEMENT CO.

in removing air bubbles from the concrete and produces a denser mass.
Tank walls should be 6 inches thick, reinforced as shown on the drawings.

In Figure 4 concrete baffle walls extend down from the cover slab a
distance of about 1 foot 6 inches. These are reinforced by means of J^-
inch round rods spaced 6 inches center to center, both vertically and
horizontally. Between the two chambers there is a weir or dividing wall
4 inches thick extending from the floor to within 6 inches of the cover slab.
This wall is provided with a lip so that the sewage cannot trickle down
the face of the wall but will at once be discharged upon the sand filter.
This lip is reinforced by bending the ends of the vertical reinforcing in
the weir wall at right angles to it and by one horizontal rod near the edge.

The sand filter is 6 inches deep and 2J^ times the length of the first
compartment. It is supported by a 3-incli concrete slab, 35 inches wide,
divided into three sections, reinforced with J^-inch round steel rods,
and contains a large number of conical openings. These are made in the
slab by setting tapered pieces of wood into the concrete before it has had
time to harden. When the slabs are placed, these openings are filled
with small pebbles to prevent the sand from passing thru to the gravel
filter below. In order to simplify the work of building the filter board,
a suggestion for another type is shown at the lower right-hand corner of
Figure 5. This board is made of 2-inch lumber with gimlet holes drilled
as shown. A 3-inch ledge projecting from the side wall serves as a support.
The three sections permit easy removal in case it is desired to secure
access to the gravel filter.

.«iX

ijl^s spaced Vcioc, \\, £*Rotb speced^ctoc,

4'OtsiTo>vOuHet

Z^i'*Roc/sl8'chc
■J'*fixispxB/6bbi

4'VkDr3in

^SECTION A-A^^

^ikntibforS I

^Gravei not .
smeller than -^

-^- SECTfON 3-B =

^SEPTIC TANK ^~

'fpR PRIVATE Res(DeNCE= —

This constmction at
sandfilkr may be used

Figure 5. Septic Tank Shown in Figure 4, illustrating the entire construction in section
as though cut along a center line following its length, also a section of the filter compartment and
plan of the whole structure with sectional view^ of another method for constructing the sand filter.

CONCRETE SEPTIC TANKS

To prevent liquid? from running along the side walls, two end \v ^
of the above slab are set into slots, in which clay has previpuslj 1'
daubed to form a tight joint. Clay may be used also to fill the open" '
between the ends of the slab and the side walls, as the slab is made ol It
width than the chamber, to permit easy removal.

Perforating this slab causes the filtered sewage to be sprinkled u
the coarse gravel filter below, and as it falls, it passes thru an 1 S-r
air spkce which is ventilated by means of air shafts at opposite sMes ol ,
structure. A difference of at l|east 8 feet in the height of these afr sli ill
advised in order to create as much draft 'in the upper portion of ;the gi
filter chamber as possible. A ventilator placed upon the tallei ^1
would assist in this respect.

Gravel in the lower filter should not be smaller tha.n one-halt
inch and is well cleaned and screwed before placing, as it" j_s Ae'^w ^
that the sewage be thoroughly aei-^ed as it passes downward' towa rd j-^i
tUe which drains the plant. Air ^hich enters by nieaiis of this, tilt r
serves to supply ventilation to the^ravel bed. If it is desired to inake
of the gravel filter feature wher^tKe natural fall'.of ground does not poi
draining, the pel^fosated sFe^bs can be omitted, raising the floor of
gravel chamber 1 foot 9 inches. The discharge from such a tank < mj
distributed over the surface of the ground with no fear that odoi*-
cause a nuisance. (It will be seen that the gravel filter in this j)
performs the same service as the gravel in the trench "A," Figure 1.1

The size of reinforcing rods, their spacing and location are all ^hc
on the drawing in such a manner that there need be no doubt as to t)
features of construction.

To those interested in septic tank constructiojj, the Universal Pi
land Cement Co., 208 South La Salle Street, Chicago, will gladly fun
large blue prints of the p'lans illustrated, together with notes del >i
construction requirements.

ill

Figure 6. Concrete Septic Tank Similar to the Type Shown in Figure 2. This shows both i
partments as they appear before placing the concrete roofer cover slab. Reinforcing rods fron
side vvralls are bent over to form part of the reinforcing for the cover.

The original of tiiis book is in
tine Cornell University Library.

There are no known copyright restrictions in
the United States on the use of the text.

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