Part 2

+--------------------------------------------------------------+ | SIPHON | +--------------------------+-----------------------------------+ |_Diameter of siphon |_Clearance under bell | | A - 3" or 4"_ | E - 2"_ | +--------------------------+-----------------------------------+ |_Diameter of bell |_Distance across U-trap | | B - 10"or 12"_ | F - 10" or 12"_ | +--------------------------+-----------------------------------+ |_Bottom of outlet |_Bottom of outlet | | to discharge line | to bottom of U-trap | | C - 20-1/2" to 25-3/4"_| G - 12" or 13"_ | +--------------------------+-----------------------------------+ |_Drawing depth |_Height above floor | | D - 13" to 17"_ | H - 7-1/4"to 11-3/4"_ | +--------------------------+-----------------------------------+ | DIMENSIONS OF DOSING CHAMBER | +-----------------+-------------------+------------+-----------+ | _Number of |_Depth below | | | | persons served_ | discharge line_[3]| _Width_[4] | _Length_ | +-----------------+-------------------+------------+-----------+ | 4 or less | 16-1/4" to 20-1/4"| 3'-0" | 6'-0" | +-----------------+-------------------+------------+-----------+ | 6 | " | 3'-0" | 7'-0" | +-----------------+-------------------+------------+-----------+ | 8 | " | 3'-6" | 7'-6" | +-----------------+-------------------+------------+-----------+ | 10 | " | 3'-6" | 8'-6" | +-----------------+-------------------+------------+-----------+ | 12 | " | 4'-0" | 8'-6" | +-----------------+-------------------+------------+-----------+ | 14 | " | 4'-0" | 9'-0" | +-----------------+-------------------+------------+-----------+ | 16 | " | 4'-6" | 10'-0" | +-----------------+-------------------+------------+-----------+

[3] Depending upon depth C of siphon.

[4] Same as single chamber tank fig. 4.

Figure 5.--Typical design for a concrete septic tank with a dosing chamber and a siphon.

Masonry units should be laid in full beds of 1:3 cement mortar and the walls and floor plastered with at least a 1/2-inch coat of 1:2 mortar. Cells of concrete blocks and tile must be filled with concrete. Masonry walls are generally 8 inches thick, and care must be taken to follow _inside_ dimensions given for concrete tanks. Directions for laying structural tile, brick, and concrete blocks can be obtained from dealers or trade associations.

Commercial tanks are suitable if they embody the essential features given in this bulletin. Capacities should be as recommended in figure 4 for concrete tanks. Proper installation and periodic servicing also are essential. Tanks badly damaged in handling should not be used. Rapid corrosion of steel tanks will result if the asphalt coating is impaired. Minor defects in precast masonry tanks may often be overcome by plastering the interior with cement mortar.

BUILDING A CONCRETE TANK[5]

[5] For information on making and placing concrete, see Farmers' Bulletin 1772, Use of Concrete on the Farm.

A convenient method of assuring correct location of the tank is to build a frame as shown in figure 6. Care is necessary to aline it with the center line of the inlet and outlet and to level it so that the distance from the bottom of the 2 by 4's on the form to the lower edge of the inlet hole in the form will permit it to be set at the grade of the house sewer. This frame is used to support the form for the tank. To avoid caving the edges, drive the stakes supporting the frame before beginning the excavation. The lumber in the frame can be used later to make part of the tank baffles.

Figure 7 shows how an inside form can be built and hung in place. The inlet and outlet tees should be carefully set and tied in place before the concrete is poured. A single length of pipe should be joined to the tee, so that the two can be set in the form as one unit. In most cases the earth walls of the excavations will serve as the outside forms unless the soil is sandy or gravelly and the excavation is deeper than 5 feet. If outside forms are used, space must also be provided for them. Forms should be constructed before the excavation is made and the tank built as soon as practical, to avoid warping of forms and caving of earth walls.

County agricultural agents, local health departments, building-material dealers, and other agencies often have forms that may be borrowed or rented.

THE EFFLUENT SEWER

The effluent sewer should be constructed in similar manner and of the same materials as the house sewer and on a slope of 1/8 inch to 1 foot. This line, however, may be laid of terra-cotta pipe, as cast-iron is not considered necessary except in unusual cases. This line should always terminate in a distribution box from which the tile lines of the disposal field lead away. For steep slopes the arrangement shown in figure 9 (p. 15) is practical. Joints must be of root-tight construction if the sewer is in the vicinity of trees or shrubs. The length of the sewer depends upon the distance from the tank to a safe site for the disposal field.

THE DISPOSAL FIELD

Correct installation of the disposal field is of great importance for proper functioning of the septic tank. Therefore, the width, depth, and spacing of the tile trenches must be carefully selected. Line of 4-inch, open- jointed, agricultural drain tile laid in shallow trenches are ordinarily used. Perforated fiber drain pipes also may be used and are obtainable in 4-foot lengths.

A distribution box with an inlet for the effluent sewer and an outlet for each individual run of disposal tile is the best means of dividing the flow. The outlet serving a large or double disposal field may be alternately opened and closed by means of a sewage switch that permits half the disposal field to work and rest alternately several weeks. A switch is especially helpful in tight soils but should not be provided unless proper maintenance is assured, so that a portion of the disposal field will not be left to handle the entire load of the system for an indefinite period. There are many variations of boxes, but figure 8 shows a practical type.

Shallow Tile Lines

The disposal tile should not be more than 18 to 24 inches below the surface, and where the ground-water level rises to the bottom of the trench special underdrains, described on page 16, are necessary. Special provisions must also be made where tight soils are encountered. These methods are described in the section entitled "Disposal methods in tight or wet soils."

The table in figure 9, together with the information given in table 1, below, may be used for estimating the number of tiles needed in any particular soil type. If there is any doubt about this requirement, a percolation test should be made in the disposal field, as follows:

Dig a hole 1-foot square and to the depth at which the tile is to be laid. This depth in most instances will be about 24 inches and should not exceed 36 inches. Fill the hole with water to a depth of 6 inches and observe the time required for the water to seep away; divide by 6 to get the average time for the water to fall 1 inch. The test should be repeated at three or four different points in the disposal field and the average time noted for all tests used. The data in table 1 can then be used to determine the number of tiles needed. Where 1 hour is required for the water to fall 1 inch the soil is totally unsuitable, and another site should be selected. Soil conditions at the time of the test may vary from year-round average conditions, and this factor must be taken into account. If the soil appears exceptionally dry, greater depths of water may be used or the test repeated in the same hole. In no case should tests be made in filled or frozen ground. Where fissured rock formations are encountered, advice should be sought from sanitation specialists.

Table 1.--_Determining tile-disposal field requirements from percolation tests_[6]

+----------------------++------------+--------------------- Minutes | Effective absorption|| Minutes | Effective absorption required | area required, per || required | area required, per for water to| person, in bottom ||for water to| person, in bottom fall 1 inch | of disposal trenches ||fall 1 inch | of disposal trenches ------------+----------------------++------------+--------------------- | _Square feet_ || | _Square feet_ | || | 2 or less | 26 || 10 | 52 | 30 || 15 | 63 | 36 || 30 | 90 | 40 || 60[7] | 120 ------------+----------------------++------------+---------------------

[6] A minimum of 150 square feet should be provided, equal to 100 feet of 18-inch trench.

[7] If more than 60 minutes, use special design with seepage pits or sand-filter trenches.

Figure 9 suggests methods of arranging the tiles in disposal fields under varying conditions and the length of tiles needed.

SIZE AND MINIMUM SPACING REQUIREMENTS FOR DISPOSAL TRENCHES +---------+----------+----------------------+-------------+ | TRENCH | TRENCH | EFFECTIVE ABSORPTION | TILE LINES | | WIDTH-W | DEPTH-D | AREA IN SQUARE FEET | SPACING-S | |IN INCHES| IN INCHES| PER LINEAL FOOT | IN FEET | +---------+----------+----------------------+-------------+ | 18 | 18 to 30 | 1.5 | 6.0 | | 24 | 18 to 30 | 2.0 | 6.0 | | 30 | 18 to 36 | 2.5 | 7.5 | | 36 | 24 to 36 | 3.0 | 9.0 | +---------+----------+----------------------+-------------+ Wider spacing of the lines desirable where available area permits

DISPOSAL-TILE TRENCH

Disposal-tile lines--Maximum length for each line 100 feet. All lines to be equal in length.

Disposal-tile lines to slope 2" to 4" per 100 feet, not over 6". Sewer-tile lines to slope 1/8" to 1/4" per foot.

DISPOSAL METHODS IN TIGHT OR WET SOILS

If the soil is heavy clay or has tight formation, yet shows some porosity from percolation tests, the efficiency of the field may be increased by placing below the tile lines 12 to 15 inches of additional filter material (washed gravel, crushed stone, slag, clean cinders, or clean bank-run gravel 3/4 to 2-1/2 inches in size). When the surface soil is tight and is underlain by porous soil, sufficient drainage is sometimes obtained for the smaller installations by omitting the tile field and providing a dry well at the end of the effluent sewer, provided the water table will not be contaminated. Larger systems under such soil conditions should have a tile field, and absorption can be increased by boring 6- or 8-inch holes down to the porous stratum and filling them with gravel or sand; the holes should be 4 to 6 feet apart. Another and perhaps the best practice is to excavate the tile trenches 4 to 6 feet and install a lower tile line, as shown in figure 10. This latter method is especially desirable if the upper tight stratum is especially thick, or if there is no porous lower stratum, or if in irrigated regions and where the disposal field is limited in area.

Where the underdrain tile is not used, the absorption capacity of the field can be increased by providing a rock-filled trench across the lower end of the tiles for the full width of the field. The depth should be not less than 5 feet and the width not less than 3 feet.

On account of the beneficial action of bacteria in the upper soil layers it is highly desirable to confine the effluent near the surface rather than to use underdrains. Purification becomes slower and less effective, the deeper the drains.

In situations where the soil contains considerable moisture or is even saturated, the field may be improved by partially encircling it with a tile line laid to serve as a drain. Such a line should be on the high side and have surface outlets for removing the water from the soil. It should not be laid so close to a disposal tile line that it will drain the sewage effluent from the disposal field onto the surface of the ground.

When the tile field is underlain by stratified rock or where under-drainage is necessary, advice should be sought from the public health authorities, as regulations in some States may not permit the use of certain methods.

CARE AND MAINTENANCE OF SEPTIC TANKS

A septic tank when first used does not need starters, such as yeast, to promote bacterial action. A good septic tank normally requires no maintenance other than a yearly inspection and an occasional cleaning. Frequency of cleaning depends on the capacity of the tank and the quantity and composition of the sewage. Tanks of the size recommended in this bulletin may require cleaning at intervals of 3 to 5 years.

The tank should be cleaned when 18 to 20 inches of sludge and scum has accumulated. If a drain has not been provided, sludge may be removed by bailing or by pumping with a sludge or bilge pump. It is not necessary to remove the entire liquid contents. Burial in a shallow pit or trench with at least 18 to 24 inches of earth cover at a point remote from water sources is the most practical method for disposing of these wastes.

A septic tank is intended to handle sewage only. Coffee grounds and ground garbage may be included if there is an ample supply of water for flushing and the tank is cleaned more frequently than would otherwise be done. The size of the tank should be increased at least 25 percent if these materials are included in the sewage.

=_Do not use matches or an open flame to inspect a septic tank, as the gasses produced by decomposing sewage may explode and cause serious injury._=

EFFECT OF DRAIN SOLVENTS AND OTHER MATERIALS

Soap, drain solvents, and other mild cleaning or disinfecting solutions used for normal household purposes cause no trouble in the tank. Constant use in large quantities, however, and disinfected wastes from the sickroom may prove harmful.

Wastes from milk rooms, strong chemicals used in sterilizing equipment or in photographic work, and the wastes from filters or water softeners not only reduce bacterial action but also cause abnormally rapid accumulations of sludge and clogging of the tile lines.

PROTECTION AGAINST FREEZING

Septic-tank systems seldom freeze when in constant use. Warm water and the decomposition of the sewage usually maintain above-freezing temperatures. In cold regions there is trouble from freezing if various parts of the system are not covered adequately. If the system is to be out of service for a period of time or if exposure is severe, it may be advisable to mound over the poorly protected parts of the system with earth, hay, straw, brush, leaves, manure, snow, or the like.

In cold regions it is not advisable to install the entire system below frost depth, as this will remove the effluent from the action of the aerobic bacteria in the upper layers of the soil and make the system generally less accessible.

New systems put into operation during very cold weather may freeze unless large quantities of hot water are discharged during the first few weeks.

SEPTIC-TANK TROUBLES

In sewage disposal, clogging of the disposal field is the most common trouble. This may be caused (1) by a tank too small for the volume of sewage, (2) by failure to clean the tank regularly, (3) by interior arrangement that does not provide slow flow through the tank or that allows scum or sludge to pass out with the effluent, or (4) by a disposal field that is too small or is incorrectly built.

The remedy for a clogged disposal field is to dig up and clean the tiles and re-lay them 3 or 4 feet to one side or the other of their former position. Sometimes a tile line can be cleaned by opening up the line at each end and flushing it thoroughly with a hose. With this method provision must be made to drain off and safely dispose of the water used for flushing.

Tile lines laid with improper slope allow the effluent to collect in a limited area and saturate the soil, causing odors. Bacteria cannot work in such areas, where the soil becomes sour, or "sewage-sick." These lines must be relaid on the correct slope. Odors or a water-logged soil may also indicate that the disposal field is too small.

House sewers frequently clog. This is due, in most cases, to roots and less frequently to trash, garbage, or other foreign materials discharged with the sewage. Greases in the sewer may cause trouble, especially when the slope is insufficient to give the sewage a cleansing velocity. Drain solvents will sometimes remove the obstruction, but more often it is necessary to clean the sewer by rodding. In some cases it may be necessary to dig up the line to reach the obstruction or, at least, to open the line so that it can be rodded from two directions. When it has been cleaned, a manhole could be built for use in case of future trouble. If stoppage is due to roots it may be necessary to re-lay the sewer with root-tight joints, or to move either the sewer or the vegetation so that roots cannot reach the line.

GREASE TRAPS

Grease traps (fig. 11) are not recommended for the average farm, because they clog easily and require frequent cleaning, but they are desirable for boarding houses and tourist camps where large quantities of grease are produced. The septic tank if of proper design and size will take care of the normal grease from most farm kitchens.

The traps must be several times larger than the quantity of greasy water discharged into them at any one time, in order to allow the greases to rise, but they should not be of less than 30 gallons' capacity.

The trap is best located in an accessible place in the basement or under the house close to the source of grease and safe from frost. Outdoor locations at shallow depths require a covering for insulation against freezing. Grease traps should be connected to the kitchen sink only and not to laundry, shower, or water-closet wastes. They must be cleaned periodically for satisfactory operation, and the outlet should be properly trapped.

DISPOSAL OF DRAINAGE FROM FIXTURES OTHER THAN TOILETS

When the farmhouse does not have an indoor toilet but does have a kitchen sink or other similar fixtures, the drainage can be disposed of as shown in figure 12. Even where septic tanks have been installed, it is sometimes advisable to have a second disposal field for other fixtures than the toilet, to avoid overloading the tank, especially where large quantities of laundry water are discharged at one time.

These wastes are not likely to create serious health hazards, but they become nuisances if discharged promiscuously on the ground surface. Such drainage should never be permitted on the watershed of a spring.

Coarse sand and gravel, 12 to 18 inches deep, may be placed on the bottom of the pit, to strain out small particles of solids, which might clog the pores of the soil. If, after a few years, the sand or gravel becomes clogged with solids, it should be replaced with clean materials.

If excessive quantities of grease are permitted to enter the sink drain, a grease trap may be advisable.

CESSPOOLS

Cesspools are cheap in first cost but high in maintenance costs and often become nuisances. They should be located at least 150 feet from wells, 15 feet from seepage pits and property lines, and 20 feet from dwelling foundations. They should never be used in the vicinity of shallow wells and, in any case, only where permitted by State regulations.

The cesspool depends for its action upon seepage into the surrounding soil and consequently is particularly unsatisfactory in tight clay soils. In more open sand and gravel soils the seepage is reduced as the pores of the soil become clogged with particles of solids, until it stops entirely, and overflowing occurs. Emptying and then cleaning the walls and floor of a cesspool do not fully open up the clogged soil pores, and overflowing can be expected to occur soon again.

Solids in cesspools must be removed from time to time by bailing or pumping and should then be buried 18 to 24 inches deep in a trench where the water supply will not be endangered. Caustic potash (lye) will to some extent liquefy solids in a cesspool. This treatment does not eliminate the necessity of removing the contents when periodic inspection shows that the cesspool is nearly full. Caustic potash converts the greases into soft soap, whereas caustic soda forms a hard soap that does not readily dissolve. The chemical treatment is not effective in liquefying solids in the pores of the soil surrounding the cesspool.

When clogging continues and cannot be corrected, in most cases the best solution to the problem would be to abandon the cesspool and install a septic-tank system with tile disposal field. The cesspool should be completely filled with stones, earth, or other solid materials to avoid possible cave-ins.[8]

[8] See The Septic Tank, p. 8.

PRIVIES

A privy when safely located and properly built and maintained is satisfactory for its purpose on the farm. Privies should be built 50 to 150 feet from the farmhouse, preferably on the opposite side of the house from prevailing winds, and at least 50 feet from the well. A site downhill from the well is generally safest. In some cases, however, the ground water may flow in a direction opposite to the slope of the surface, in which case the privy should be built on the other side of the well. Direction of flow may sometimes be learned from soil surveys, well-driller's data, or other similar sources. A distance of at least 6 feet from fences or other buildings allows for proper mounding of the privy and keeps it away from roof drainage from adjacent buildings.

Good, tight construction with screened ventilators keeps insects and birds from entering, prevents rapid deterioration of the building, and provides greater comfort for the user.