Part 6

Cesspools should be emptied and cleaned at least once a year and the contents given safe burial or, with the requisite permission, wasted in some municipal sewerage system. After cleaning, the walls and bottom may be treated with a disinfectant or a deodorant.

SEPTIC TANKS.

A tight, underground septic tank with shallow distribution of the effluent in porous soil generally is the safest and least troublesome method of treating sewage upon the farm, while at the same time more or less of the irrigating and manurial value of the sewage may be realized.

The late Prof. Kinnicutt used to say that a septic tank is "simply a cesspool, regulated and controlled." The reactions described under the captions "How sewage decomposes," "Liquefying closet," and "Cesspools" take place in septic tanks.

In all sewage tanks, whatever their size and shape, a portion of the solid matter, especially if the sewage contains much grease, floats as scum on the liquid, the heavier solids settle to form sludge, while finely divided solids and matter in a state of emulsion are held in suspension. If the sludge is retained in the bottom of the tank and converted or partly converted into liquids and gases the tank is called a septic tank and the process is known as septicization. The process is sometimes spoken of as one of digestion or rotting.

=History.=--Prototypes of the septic tank were known in Europe nearly 50 years ago. Between 1876 and 1893 a number of closed tanks with submerged inlets and outlets embodying the principle of storage of sewage and liquefaction of the solids were built in the United States and Canada. It was later seen that many of the early claims for the septic process were extravagant. In recent years septic tanks have been used mainly in small installations, or, where employed in large installations, the form has been modified to secure digestion of the sludge in a separate compartment, thus in a measure obviating disadvantages that exist where septicization takes place in the presence of the entering fresh sewage.

=Purposes.=--The purposes of a septic tank are to receive all the farm sewage, as defined on page 4, hold it in a quiet state for a time, thus causing partial settlement of the solids, and by nature's processes of decomposition insure, as fully as may be, the destruction of the organic matter.

=Limitations.=--That a septic tank is a complete method of sewage treatment is a widespread but wrong impression. A septic tank does not eliminate odor and does not destroy all organic solids. On the contrary, foul odors develop, and of all the suspended matter in the sewage about one-third escapes with the effluent, about one-third remains in the tank, and about one-third only is destroyed or reduced to liquids and gases. The effluent is foul and dangerous. It may contain even more bacteria than the raw sewage, since the process involves intensive growths. As to the effects upon the growth and virulence of disease germs little is known definitely. It is not believed that such germs multiply under the conditions prevailing in a septic tank. If disease germs are present many of their number along with other bacteria may pass through with the flow or may be enmeshed in the settling solids and there survive a long time. Hence the farmer should safeguard wells and springs from the seepage or discharges from a septic tank as carefully as from those of liquefying closets and cesspools.

=Further treatment of effluents.=--The effluent of a septic tank or any other form of sewage tank is foul and dangerous. Whether or not the solids are removed by screening, by short periods of rest, as in plain or modified forms of settling tanks, or by longer quiescence, as in septic tanks, the effluent generally requires further treatment to reduce the number of harmful organisms and the liability of nuisance. This further treatment usually consists of some mode of filtration. In the earliest example of such treatment the sewage was used to irrigate land by either broad flooding or furrow irrigation. By another method the sewage is distributed underground by means of drain tile laid with open joints, as illustrated in figures 17, 29, and 32.

Artificial sewage filters are composed of coarse sand, screened gravel, broken stone, coke, or other material, and the sewage is applied in numerous ways. Since filtration is essentially an oxidizing process requiring air, the sewage is applied intermittently in doses.

Artificial filters of various types are well described and illustrated in Public Health Bulletin No. 101, "Studies of Methods for the Treatment and Disposal of Sewage--The Treatment of Sewage from Single Houses and Small Communities." U. S. Public Health Service, December, 1919.

If properly designed and operated, filters of sand, coke, or stone are capable of excellent results. Under the most favorable conditions it is unwise to discharge the effluent of a sewage filter in the near vicinity of a source of water supply. Under farm conditions filters are usually neglected or the sewage is improperly applied, resulting in the clogging and befouling of sand filters and the discharge from stone filters of an effluent which is practically as dangerous and even more offensive than raw sewage. Moreover unless the filters are covered there are likely to be annoying odors, and there is always the possibility of disease germs being carried by flies where sewage is exposed in the vicinity of dwellings. Hence it seems more practical for the farmer, avoiding the expense of earth embankments or masonry sides and bottom for a filter bed, to waste the tank effluent beneath the surface of such area of land as is most suitable and available. This method of applying sewage to the soil or subsoil is often spoken of as subirrigation, but subsoil distribution of sewage is different in principle and practice from subirrigation for the increase of crop yields. Subirrigation is rarely successful unless the land is nearly level, the top soil porous and underlaid with an impervious stratum to hold the water within reach of plant roots, and unless a relatively large quantity of water is used and the work is skillfully done. On the other hand, the quantity of sewage on farms being small, it may be wasted in hilly ground, which should be as porous, deeply drained, and dry as possible.

=Parts of a system.=--The four parts of a septic-tank installation with subsurface distribution of the effluent are outlined in figure 19: (1) The house sewer from house to tank; (2) the sewage tank consisting of one or more chambers; (3) the sewer from tank to distribution field; (4) the distribution field, where the sewage is distributed and wasted, sometimes called the absorption field. These parts will be discussed in the order named, although the last should have the first consideration.

=House sewer.=--The length will vary with the slope of the ground and position of buildings, well, and distribution field. Fifty to 100 feet is a fair length; a greater is still more sanitary. Wherever possible the house sewer should be laid straight in line and grade. Figure 20 shows how this work may be done. Suppose the distance from A to E be 100 feet; that grade boards be set 25 feet apart crosswise of the trench at A, B, C, D, and E; that the ground at A be 4 feet lower than at E; that the top of the sewer be 2-1/2 feet below the surface of the ground at A and 4-1/2 feet below the surface of the ground at E; the fall of the sewer between A and E is 2 feet (4 + 2-1/2 - 4-1/2 = 2). If the fall in 100 feet be 2 feet, in 25 feet it is one-fourth as much, or 6 inches. Hence, grade board B is 6 inches higher than grade board A, C is 6 inches higher than B, and so on to E. The top edges when all the boards are set with a carpenter's level and fastened in position should be in line. The grade thus established may be any convenient height above the top of the proposed sewer, and the measuring stick used to grade the pipe is cut accordingly. This height is usually a certain number of whole feet. Fixing the line of the sewer is a mere matter of settling nails in the top edges of boards A and E directly over the center of the proposed sewer and tightly stretching a fish line or grade cord; nails should be set where the cord crosses boards B, C, and D.

If the cellar or basement contains plumbing fixtures, the house sewer should enter 1 to 2 feet below the cellar floor. If all plumbing fixtures are on the floors above, the sewer may enter at no greater depth than necessary to insure protection from frost outside the cellar wall. Digging the trench and laying the pipe should begin at the tank or lower end. The large end of the pipes, called the hub, should face uphill, and the barrel of each pipe should have even bearing throughout its length. Sufficient earth should be removed from beneath the hubs to permit the joints to be made in a workmanlike manner.

The house sewer may be vitrified salt-glazed sewer pipe, concrete pipe, or cast-iron soil pipe. The latter, with poured and calked lead joints makes a permanently water-tight and root-proof sewer, which always should be used where the vicinity of a well must be passed; 4, 5, or 6-inch pipe may be used, depending mainly on the fall and in less degree on the quantity of sewage discharged. As a measure of economy the 4-inch size is favored for iron pipe. If vitrified pipe is used, either the 5 or 6 inch size is preferable, as these sizes are made straighter than the 4-inch size and are less liable to obstruction. Of the two the 5-inch size is preferable. The fall in 100 feet should never be less than 2 feet for 4-inch size, 1-1/2 feet for 5-inch size, 1 foot for 6-inch size.

Figure 21 shows methods of making good joints. A, B, C, D, E, F, and G are ordinary sewer pipe joints; H, is cast-iron soil pipe.

A shows the use of a yarning iron to pack a small strand of jute into the joint space, thus centering the pipes and preventing the joint filler running inside. The joint surfaces should be free of dirt and oil. The jute is cut in lengths to go around the pipe; a small strand is soaked in neat Portland cement grout, then twisted and wrapped around the small end of the pipe to be pushed into the hub of the last pipe laid. After the pipe is pushed home the jute is packed evenly to a depth of not over 1/2 inch, leaving about 1-1/2 inches for the joint filler. Old hemp rope or oakum dipped in liquid cement or paper may be used in place of jute, and the packing may be done with a thin file or piece of wood.

B shows the use of a rubber mitten or glove to force Portland cement mortar into the joint space. The mortar should be thoroughly and freshly mixed in the proportion of one volume of cement to one volume of clean sand and should be pressed and tamped to fill the joint completely.

C shows a section of finished joint. The fresh mortar should not be loosened or disturbed when laying the next pipe.

D shows method of pouring a joint with grout, which is quicker, cheaper, and better than using a rubber mitten. A flexible sheet-metal form or mold, oiled to prevent the grout sticking, is clamped tightly around the joint and is completely filled with grout consisting of equal parts of Portland cement and clean sand mixed dry, to which water is added to produce a creamy consistency. The pipes should not be disturbed and the form should not be removed for 24 hours.

E shows a section of grouted joint, well rounded out, strong, and tight.

F shows the use of a pipe jointer for pouring a hot filler. The pipe jointer may be an asbestos or rubber runner or collar or a piece, of garden hose clamped around the pipe leaving a small triangular opening at the top. The jointer is pressed firmly against the hub, and any small openings between the jointer and pipe are smeared with plastic clay to prevent leakage of the filler. A clay dike or funnel about 3 inches high built around the triangular opening greatly aids rapid and complete filling of the joint space. The filler may be a commercially prepared bituminous compound or molten sulphur and fine sand. The former makes a slightly elastic joint; the latter a hard unyielding joint. With good workmanship both kinds of joint are practically water-tight and root-proof, and cost about the same as cement mortar joints. The filler is heated in an iron kettle over a wood, coke, or coal fire. It should be well stirred, and when at a free running consistency should be poured with a ladle large enough to fill the joint completely at one operation. As soon as the compound cools the jointer is removed. Sulphur-sand filler is made by mixing together dry and melting equal volumes of ordinary powdered sulphur and very fine clean sand, preferably the finest quicksand. A 5-inch sewer pipe joint requires from three-tenths to nine-tenths of a pound (according to the kind of pipe) of sulphur, worth 3 to 5 cents per pound, and a like quantity of sand. From 1/2 to 1-1/2 pounds of bituminous filler are required for a 5-inch pipe joint.

G shows section of finished joint.

H shows the use of a pouring ladle in making lead joints in cast-iron soil pipe. This pipe is in lengths to lay 5 feet, and the metal of the barrel is 1/4 inch thick. The joint is yarned with dry jute or oakum, as described above, and is poured full with molten, soft, pig lead to be afterwards driven tightly with hammer and calking tools. About 1 pound of lead for each inch in diameter of pipe is required. Prepared cements of varying composition have proved effective,, and, as they require no calking, are economical. Among the best is a finely ground, thoroughly mixed compound of iron, sulphur, slag, and salt.

I is a home-made pipe jointer or clay roll for use in pouring molten lead. A strand of jute long enough to encircle the pipe and the ends to fold back, leaving an opening at the top, is covered with clay moistened, rolled, and worked to form a plastic rope about 1 inch in diameter. The jointer gives the very best results but must be frequently moistened and worked to keep the clay soft and pliable. The jointer shown in F is frequently used for pouring lead joints.

Obstructions in house sewers are frequent. Among the causes are broken pipes, grade insufficient to give cleansing velocities, newspaper, rags, garbage, or other solids in the sewage, congealing of grease in pipes and main running traps (house sewer traps), and poor joint construction whereby rootlets grow into the sewer and choke it. Good grade and good construction, with particular care given to the joints, will avert or lessen these troubles. The sewer should be perfectly straight, with the interior of the joints scraped or swabbed smooth. When the joint-filling material has set, the hollows beneath the hubs should be filled with good earth free of stones, well tamped or puddled in place. It is important that like material be used at the sides of the pipe and above it for at least 1 foot. The back filling may be completed with scraper or plow. No running trap should be placed on the house sewer, because it is liable to become obstructed and it prevents free movement of air through the sewer and soil stack. Conductors or drains for rain or other clean water should never connect with the house sewer, but should discharge into a watercourse or other outlet.

Where obstruction of a house sewer occurs, use of some of the simple tools shown in figure 22 may remedy the trouble. It is not likely that farmers will have these appliances, except possibly some of the augers; but some of them can be made at home or by a blacksmith, and most of them should be obtainable for temporary use from a well-organized town or city sewer department. The purpose of the several tools shown is indicated in the notation.