Introduction and Background

CALIFORNIA AGRICULTURAL EXTENSION SERVICE CIRCULAR 82 DECEMBER, 1933 A SEPTIC TANK FOR FARM HOMES H. L. BELTON AnD J. P. FAIRBANK Cooperative Extension work in Agriculture and Home Economics, College of Agriculture, University of California, and United States Department of Agriculture cooperating. Distributed in furtherance of the Acts of Congress of May 8, and June 80,1914. B, H. Crocheron, Director, California Agricultural Extension Service. THE COLLEGE OF AGRICULTURE UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA in 1 foot of complete system. Fig. 1—Cross A SEPTIC TANK FOR FARM HOMES' I. L, BELTON? anv J. P. FATRBANK* The convenience of water piped into the house is enjoyed by nearly three-fourths of the farm families in California. The full advantage of having running water in the dwelling, however, ean be obtained only if the sewage disposal system is safe and free from annoyances. A satis- factory method of sewage disposal for most rural homes is a septic tank and a subsurface drainage system. Leaching cesspools, although suitable in some instances, are not generally recommended because of the danger of contaminating wells. Under many conditions, furthermore, they fill up in time because the surfaces of the pit become watertight. The septic tank is but one unit of the complete sewerage disposal sys- tem, the other important parts being the sanitary plumbing in the house, the plumbing to the septic tank, and the subsurface drainage system (fig. 1). : All sewage and waste water from the plumbing fixtures flow into the septic tank, where the more solid materials are reduced in volume and are largely changed to liquid by the action of anaerobic bacteria. The liquid effluent flows from an outlet near the top of the tank into a drain- em, where it filters into the soil. Although the liquid entering the disposal line is nearly clear, it is not pure water and should not be allowed to enter wells or other sources of domestic water supply. The final purification takes place in the upper layer of the soil, not only by filtering, but also by the action of bacteria. If exposed to the open air, as in open ditches or pools, the liquid will give off objectionable odors and will be a source of contamination that may he carried by inseets or animals. THE FUNCTION OF THE SEPTIC TANK The septic tank is merely a water-tight container that provides a proper environment for the bacteria. It should quietly retain the sewage and waste water two to four days. Agitation of the contents is minimized by bafiles across the tank that also serve to prevent solids from escaping through the outlet. 2 This publication supersedes Circular 270, “A Farm Septic Tank,” now out of print. 2 Associate in Agricultural Enginee xtension Specialist in Agricultur Engincering. [3] + CantrorNt\ AGricuLruRAL EXTENSION SERVICE [Ci. 82 When additional sewage enters the tank from the house, the liquefied products resulting from the bacterial action flow out into the drain line. A portion of the solids that is never completely liquefied forms a black sludge, which generally settles in the bottom but which is in part car- ried out in the effluent. Because of the gradual aceumulation of this sludge, a septic tank must be thoroughly cleaned at intervals depending upon its size and upon the amount of sewage. The scum or mat that Reinforcement L_cé sg rods_or heavy hog fencing, OPS Pere SD Kent Outlet we ) || Qoening XB \3 pcs 2°x/0"_} Bottom uy So/Me . 24 Fig. songitudinal view of septic tank, The size shown is recommended for not more than 7 persons. usually forms on the surface of the liquid does not, however, indicate that the tank needs cleaning. Typhoid stools and other infectious matter should be disinfected he- fore disposal through the toilets. Excessive amounts of disinfectants should not be added to the sewage, for they may destroy the useful hae- teria in the tank. TYPE OF TANK The chief requirements are that the tank he large enough, that it be water-tight, adequately baffled, accessible for cleaning, and constructed of materials which do not quickly decay or rust. Simplicity is desirable. Ready-built septie tanks of different types and sizes are manufac- tured commercially and are sold ready to install. They are made of steel, of wood, and of large concrete or vitrified clay pipe; and, in general, they have proved satisfactory when correctly installed. As their most common fault is the lack of capacity, the purchaser should select a size suitable for his conditions. The net capacity should equal at least twice A Septic TaNK ror Farm Homes 5 the amount of water used daily in the house. Since this amount averages from 20 to 40 gallons per day per person, for a two-day minimum reten- tion period the septic tank should have a capacity of at least 40 to 80 gallons (514 to 11 eubie feet) per person. Fig. 3.—Halt-seetion view of septic tank. A HOMEMADE SEPTIC TANK reular deseribes a simple but satisfactory type of septie tank, ly adopted in California during the past fifteen years. As shown 2and 3), it is made of poured concrete; but it may be made of rot- stant wood. The following table givés the inside measurements of three different 6 CauirorniA AcricunruraL Exrension Servicr (Cir. 82 sizes of tanks. The first is recommended for a family of 4 to 7 persons, the second for 8 to 11, and the third for 12 to 15 persons in the house- hold. TABLE 1 RECOMMENDED Sizes or Tanks Inside measurements ‘Thickness of concrete Number of — — No, persons ; Width | Length | Depth | Sides" | Ends | Floor 7 | det Jeet feet | inches | inches | inches | inches 1 | 4t07 3 7 4 4 4 4 3 2 8toll | 33 9 | 4 5 5 | 4 3h 3 | 121015. 4 10 ‘js 6 4 4 One septic tank may serve two or more dwellings when the total num- her of persons does not exceed the rated capacity. TANK LOCATION The septic tank is normally located not further than 50 feet from the house but may be much eloser.* It should not be under a foundation, or under permanent walks, or driveways which may interfere with uncoy- ering it for cleaning. A leaky septic tank near a well or spring is, of course, dangerous. The tank is usually constructed so that the cover is flush with the ground, or slightly lower. The top of the outlet line, accordingly, will be 12 to 16 inches below the ground level, a depth that has proved satis- factory when good soil conditions for drainage exist. A high water table at certain seasons of the year, or heavy clay loam, or hardpan near the surface may make it advisable to keep the top of the tank above ground level, thus obtaining a drainage outlet nearer the surface. The fall of the sewer pipe from the plumbing fixtures into the septic tank should be not less than 14 inch to the foot. This standard must be considered in determining the location of the tank and the depth below the ground surface. If the tank is located a considerable distance from the house and the ground is level, it must be placed deep enough to provide sufficient fall for the sewer line. This arrangement necessitates a deeper drainage sys tem, which in general is undesirable and increases the cost. The enter the tank on either side of the center in the end wall if that placing makes for convenience. ewer m: 4 One city has an ordinance requiring septic tanks to be at least 10 feet from the foundation. Within city limits the sanitary plumbing code of the municipality should be recognized, . A Septic Tank vor Farm Homes 7 DIRECTIONS FOR BUILDING The following detailed directions for building apply to the No, 1 tank for the average family up to7 persons. For the No. 2 and No. 3 tanks the dimensions should be increased in accordance with those shown in table 1. Preparing for Excavation.—Select the tank location. Lay two planks 3 feet 8 inches apart (fig. 4). Level and hold them in a flat position Fig. 4.—The 2 x 10 inch planks laid about the hole are later used as baffie boards. against stakes driven into the ground. Across the planks nail two 1 x 6 inch hoards to form a rectangular frame with inside dimensions 7 feet 8 inches by 3 feet 8 inches (fig. 4). This frame about the top of the hole prevents the crumbling of the earth on the freshly poured concrete dur- ing construction, and provides a working edge from which a plumb bob may be suspended to aid in digging perpendicular walls. If the earth is such that it might cave in, the hole must be made larger to accomodate an outside form. Under ordinary conditions the hole is excavated to a depth of from 4 feet 7 inches to 5 feet below the bottom of the frame. This places the tank 0 to 5 inches, and the top of the outlet pipe 12 to 16 inches, below the surface. Local conditions, however, determine the depth of the tank. 8 CanirorNiA AGRICULTURAL EXTENSION SERVICE [Crr. 82 The Forms.—The forms are so designed that they can be readily re- moved in sections without damage and used repeatedly. This feature makes them more valuable to a community. Many farm centers own sets of forms, which they rent at a nominal charge to pay for the lumber Fig. 5.—View of form for septic tank. and minor repairs. Sets have been used twenty to thirty times. Oiling the forms before use adds to their life and prevents concrete from stick- ing to the wood. The forms should be made of common lumber surfaced on one side, the outside measurements to correspond to the inside measurements of the tank. Figure 5 gives the necessary dimensions for constructing the inside form. A Septic Tank ror Farm IlomMes 9 Side Panels —The sheathing, which may be 1x6 inches, is nailed firmly to the 2 4 inch studding (A and D, fig. 5). The 1 x 2 inch baffle cleats (F, fig. 5) are now nailed on the side panels to form grooves for Fig, 7—The side-wall sheathing should be well nailed, and the boards drawn close together. the bafile boards. They should be slightly beveled on the edges to insure easy removal of the side panels. Other views of the construction are shown in figures 6, 7, 8, and 9. 10 Cauirorni1a AaricutturAL ExTeNnsion SERVICE (Cir. 82 Cross Braces.—Six 1x6 inch eross braces (E, fig. 5) hold the side panels to the proper width. The three lower braces should be 6 inches above the bottom of the form. End Panels.—The end panels, which are constructed as shown in fig- ure 10, are held to the 2 3 inch studding (B. fig. 5) which fits against the studding A and the end of the side-wall sheathing. Two 8d common nails (C, fig. 5) at each corner hold the studding B in proper position. Four 6d nails are sufficient to hold the end panel to the studding B. Fig. 8.—Nail the 1x2 inch baffie cleats firmly in position after trimming the side-wall sheathing. Corner Strips —The corner strips (@, fig. 5) are held to the studding B by one small nail each, tacked near the top. These nails should be withdrawn before they are covered with concrete. Hanging the Form.—For convenience in setting the form in posi- tion, the studding A (figs. 5 and 11) should project 2 feet above the top edge of the wall sheathing. After being lowered into the hole, the form should be blocked up level to allow for a 4-inch bottom of conerete, and squared up in the hole so that all walls will be of the same thickness. Next, 1x 6 inch hanging boards (fig. 12) are nailed firmly to the 2x4 studding A and to the 2 x 10 inch plank frame that was placed about the top edge of the hole. The blocking is then removed, and the form is ready for the concerete. Construction of Tank.—The tank should be constructed with 4-inch sides and 4-inch bottom. The top must be 3 inches thick and reinforced. A 1:21%4:4 mixture of conerete material is recommended; that is, 1 sack A Septic TANK ror Farm Homes 11 or 1 cubie foot of cement, 24% cubie feet of sand, and 4 cubic feet of crushed rock. Both the sand and the rock should be clean and free from organic matter. The sand should vary from fine to 14 inch in size; the aY_ATS oS Vig. 9.—Assembling side-wall forms and placing the 1x 6 inch cross ties in the proper position. rock, from 84 to 1 inch. Clean, well-graded gravel may be substituted for the rock and sand. This should be mixed in a proportion of 1 sack of cement to 41% cubic feet of gravel. Enough water should be added to give the entire mixture a jelly-like consistency. Too much water is harm- ful, for the strength of the conerete is reduced by adding more water than is necessary for a workable mixture. The concrete should be thor- 12 Canmwornt AGRICULTURAL EXTENSION SERVICE k Ww Ponels 1s 3S" minus twice the width of corner strip O" iy 40" Vig. 10.—End panel. ner, hold the end ps figure 5. Four 6d x is to the 2 Hs, one at each cor- 3 inch studding B, [Cir. 82 Fig. 11.—The completed form ready to be lowered into the hole, A Sepric Tanck vor Farm Homes 13 oughly tamped as it is poured, thus insuring smooth, water-tight walls; a 1x2 inch V-shaped strip will be found convenient for tamping and working it into place. The conerete should be poured evenly about the walls. (Do not erowd the forms out of alignment by pouring too much conerete in one place.) When the concrete is within 11 inches of the top at the inlet end and 14 inches at the outlet end, the 6 x 6 x 4 inch boxes 210" Baffle-board plank- End view of completed form suspended in the hole. (fig. 5) should be placed. Small nails driven into the form before it is lowered into the hole will show the exaet position of these boxes.