SPORTS AFIELD - March 1965

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SECOND HOME FOR SPORTSMEN


BY JERRY GEERLINGS

SEWAGE DISPOSAL



     It's no longer a guessing game. Or a matter of being lucky. If a sewage-disposal system is planned and installed in accordance with recognized standard practice, its efficacy can be accurately predicted. The danger of pollution to sources of drinking water, and the possible spreading of disease, has led in many parts of the country to local jurisdiction over the installation of septic systems. So before you pay for one, find out all about local codes, permits and inspections.
     Any waste-disposal system worth installing should be so trouble-free you will never know it's there. And for the avoidance of future problems, the system's capacity should be greater than your present estimate of the total number of persons who will ever make use of your second home during any 24-hour period. The reason: it isn't possible to enlarge the capacity of a disposal system at a later date to meet any increased requirements (which might arise, for instance, from a doubling of the sleeping accommodations).
     A sewage-disposal system justifies its cost by preventing the contamination of drinking water, and thus precluding the transmission of such diseases as typhoid fever, dysentery and various types of diarrhea. A layout for all the components of a system for the cabin or second home must take into account the three principal variables of any site: (1) the porosity of the soil; (2) the level of the water table (distance at which surface water flows below the grade level after spring thaws or heavy rainstorms); (3) the existence and size of a relatively level area for the disposal field (trenches with buried drain tile). If you are land hunting, think twice before buying a magnificent rock outcropping without any soil area. If you already own land, take the disposal system into account when situating the house, the well and the drive.
     The disposal system (see Illustration 1) consists of the following components: house drain, house sewer, septic tank, outlet sewer, distribution box, disposal field and possibly one or more leaching pools (or seepage pits).
     The house drain is the four-inch-diameter cast-iron soil pipe that conducts the water and waste from the various plumbing fixtures of a house to a point about five feet beyond the foundation wall. It should have a cleanout (at the transition from vertical to horizontal) accessible from basement or crawl space, so that any stoppage can be cleared with a plumber's "snake," without the necessity of resorting to digging.
     The house sewer is the connection between the end of the cast-iron house drain and the septic tank. Usually it consists of a six-inch-diameter bell-and-spigot tile sewer pipe, with all joints well filled with mortar (see Illustration 2). A band of mortar around each joint (one inch thick and about three inches wide) will exclude tree and shrubbery roots. Cast-iron pipe should be used when the house sewer is five feet or less from a basement or foundation wall, or when it runs under a driveway, or when it is within 50 feet of a well. Both house drain and house sewer should slope one inch every four feet, because this pitch has been found to produce the best rate of flow for waste entering the septic tank. Also, both house drain and house sewer must be laid on well-compacted earth.
     To minimize the possibility of any stoppage in the sewer, there should preferably be a straight line extending from the cleanout of the house drain through the drain and all the segments of the house sewer to the septic tank. When this is impossible, it's wise to provide a cleanout at every bend that is sharper than 90 degrees. It's good insurance to provide a cleanout in the sewer line just before it enters the septic tank. (In your basement or crawl space you'll probably find such a cleanout, with a threaded cap, on the sewer line near the location where it intersects the basement wall.)
     The septic tank is an enclosed watertight chamber in which waste and sewage is contained until bacterial action (about 24 hours) converts the solid matter into liquids, gases and sludge (see Illustration 3). The liquids, or effluents, flow out of the side of the tank (opposite where the waste entered) into the dis-

Figure 1
Illustration 1.


Figure 2
Illustration 2.


tribution box. From there they flow into the disposal field, where the liquids seep through open joints in tile and are absorbed by stone aggregate or gravel that fills the trenches. Gases escape to the air space at the top of the tank, then pass out through the house sewer and up the vertical vent of the plumbing system and are discharged into the air above the roof of, the house. The sludge settles to the bottom of the tank, where it forms a tarlike substance that must be periodically pumped out or otherwise removed. Usually this requires doing about once every three years, but actual examination with appropriate equipment is necessary for a dependable determination. Fats and greases collect as scum at the top of the tank's liquid content.
     Septic tanks can be obtained ready for installation, made either of precast concrete or of specially coated steel (usually cylindrical and vertical in shape for domestic use). These units have been carefully engineered as the result of years of experience. Effective bacterial action is dependent upon an absence of fresh air and the presence of baffles to minimize turbulence caused by inflowing sewage and outflowing 'liquids.
     The recommended net working capacity of septic tanks is often given in relation to the number of bedrooms of a house. This is not particularly applicable to a cabin or second home, which may accommodate many guests on occasion, yet have relatively few or no occupants for long periods. It is preferable here to select the net tank capacity in relation to the maximum number of persons who may be overnight visitors during any single 24-hour period. A minimum of 40 to 50 gallons of waste per day per person is a figure used by various state health departments.
     The smallest precast concrete tank recommended has a 750-gallon capacity. Also, the Portland Cement Association has a brochure titled "Concrete Structures for Farm Water Supply and Sewage Disposal" that gives good working details (illustrated with both drawings and photos) for cast-in-place concrete septic tanks, as well as formulas for recommended concrete mixes. In addition to the use of precast or poured concrete, heavyweight concrete blocks or brick, laid on a solid poured-concrete foundation, will be satisfactory if the joints are well filled with mortar. The interior of the tank should be given two coats of 1/4-inch-thick portland cement-sand plaster.
     All septic tanks must have tight-fitting covers. Where rectangular built-on-the-job tanks are used, covers can be made by the use of poured-concrete planks, each about 3/4 inches thick, 12 inches wide and slightly longer than the width of the outer tank. Each plank should be reinforced with three 3/4-inch round bars, spaced about four inches apart horizontally and one inch above the bottom surface. Since it will be necessary to remove the concrete cover units when the tank is cleaned, make the slabs longer than the tank width, so that you will be able to get a grip on the protruding ends, or else embed galvanized-iron rings into the concrete while it is still soft to serve as handles. The joints between adjacent cement units should be filled with roofing cement to form a watertight seal.
     Stock steel tanks for domestic use (vertical, of cylindrical design) are made with net capacities of 300, 500, 600 and 750 gallons. They are provided with removable steel covers and interior baffles.
     The location of the septic tank and disposal field should always be downhill from the drinking-water supply. On a relatively level site, water-supply source and septic tank should be separated by a minimum of 50 feet, and preferably more. Although surface water will follow the contours of the ground, the movement of water below the surface generally is in the direction of the slope of the water table. Since you can't determine this merely by looking at the surface, and making tests is too costly, prudence indicates providing ample horizontal distance between well and septic tank, plus installing an efficiently functioning disposal field. A septic tank should not be located closer than five feet to any building, for at least two reasons: (1) the runoff water from the roof can make the entire area soggy, in which case surface water might seep into the tank; (2) there should be good accessibility for the periodic removal of sludge. Obviously, a septic tank should never be in an area that is swampy or subject to flooding.
     A septic tank doesn't purify sewage or remove a large percentage of bacteria. But it does provide a means for decomposing solids. Whenever sewage flows into the tank, an equal displacement in liquid form will be forced out. If the tank is sufficiently large to cope with the inflowing waste, only liquids will flow out to the distribution box and from there to the disposal field-thus there will be no clogging caused by solids.
     Tanks need not be inspected for two years after being cleaned, but it's well to do so annually thereafter. If too much scum or sludge builds up, so that the level of either is too close to the bottom of the outlet, some solids will find their way into the disposal field and clog the tile.
     The usual method of cleaning septic tanks employed by companies that provide this service is pumping the contents out to a tank truck for later disposal in accordance with the regulations of the local health authorities. It is usually permissible to bury tank contents in remote, uninhabited places, but never in any storm sewer or in any location where the contents could pollute a stream, lake or the like.

Figure 3
Illustration 3. Here is a section through a rectangular septic tank; it shows such critical dimensions as the house-sewer inlet's being three inches higher than the outlet sewer pipe.


Figure 4
Illustration 4. Here are four common disposal-field layouts. A, B and C are suitable for level sites, D best suited for sloping ground.


     It is necessary to leave a small amount of sludge in a septic tank when it is cleaned, to ensure the continued propagation of the bacteria that feed on the solids. Never wash out a tank or disinfect it after cleaning, because this would eliminate the useful bacteria. Expert opinion maintains that the decomposition in septic tanks is not improved by the use of special products that contain sodium hydroxide or potassium hydroxide, because the increase in alkalinity may retard the decomposition of solids, as well as alter the effluent in such a manner that the soil adjacent to the trenches of the disposal field will clog at an accelerated rate. The small quantities of lye or caustics occasionally used in homes to clean toilets or sink drains don't have a marked adverse effect on septic-tank performance.
     In the average cabin or second home, the waste from all plumbing fixtures (kitchens, baths and laundry fixtures) should be conducted to a single septic tank. But roof drains, foundation drains, garage drains and any source of oily waste (such as a garage floor) should not be piped to the septic tank. Anything that will not decompose quickly (such as rags, paper towels, wrapping paper or newspapers) should not be flushed down a toilet.
     The outlet sewer is the watertight connection between septic tank and distribution box. It should be made of the same impervious material (four-inch bell-and-spigot sewer pipe with well-mortared joints, concrete pipe or cast-iron pipe) as the house sewer and should be pitched about one inch every 25 feet. In a properly functioning system, only liquids will pass from the septic tank to the distribution box.
     A distribution box is a small tank, supported on a concrete footing, that receives the liquids or effluent from the septic tank via the outlet sewer. It serves two principal purposes: (1) it equalizes the flow of liquids into several disposal lines of tile; (2) it provides a convenient inspection location for determining whether or not the septic tank is functioning satisfactorily. If it is, there will be fairly clear liquids only (no solids) in the distribution box. Sometimes a small disposal system is installed with a single line of tile and without a distribution box; but for the small saving in extra materials and labor, this omission of the distribution box is not considered genuine

Figure 5
Illustration 5.


economy. A stoppage produced by a single clog of solids just beyond the septic tank will cause the liquids from the tank to be forced up to ground level, where they will stagnate to form an obnoxious pool. Moreover, there will be no simple means of discovering where the stoppage has occurred. If there is a distribution box, the search can be narrowed down at once: (1) the presence of solids indicates that the tank needs cleaning because some of the solids have been forced through the septic tank's outlet, and the stoppage may very well be located between septic tank and distribution box; or (2) if there are only liquids in the distribution box but it is overflowing, the stoppage is in one or more of the lines of tile.
     The disposal field consists of one or more lines of drain tile, with open joints, laid in trenches. The liquids flow from the distribution box into the lines of tile and seep through the tile joints, to be absorbed by the gravel or crushed rock that surrounds the tile in the trenches. The complete disposal of waste liquids below grade is dependent upon adherence to established trench techniques and materials, plus the absorptive qualities of the earth in which the trenches are dug. Before planning a trench layout, you'll need to know how many lineal feet are required-and to determine this, it's necessary to know the absorption or percolation rate of the soil. The amount of liquid that flows from the tank and the rate at which it can be absorbed in the trenches establish the number of lineal feet of tile required.
     The absorption or percolation rate should be determined at about six scattered locations where the disposal field will be located. A fence-pole digger or auger can be used to make holes sunk to the approximate depth of the bottom of the trenches (not less than 18 inches below grade). The sides of each hole should be roughened where the earth has become smeared or compacted. Then about two inches of coarse sand or fine gravel should be poured into each hole, plus sufficient water so that a 12-inch depth is maintained overnight. To make the test the day following, see that there is about a six-inch depth of

Figure 6
Illustration 6.


water in each hole, then record how many minutes it takes for the level to drop one inch. If it takes over an hour, the soil is not suitable for disposal trenches. Take the average of all holes, and use the table below.

Table 1
Table 1.


     Trenches should be kept ten feet away from the house or property lines, 100 feet away from the drinking-water-supply well and 50 feet from any stream. Trenches that are 18 inches wide should be six feet apart, and if 24 inches wide then seven feet apart. A sealed line (no open joints) should extend from the distribution box to the first drain tile of each line. The individual tiles may be 12-inch lengths of four-inch-diameter agricultural drain tile, or two-to-three-foot lengths of vitreous-clay sewer pipe or perforated nonmetallic pipe. Single lines of tile preferably should not be longer than 60 feet, with 100 feet a maximum (see Illustration 4).
     To be effective, the trenches must be carefully constructed. For the natural absorptive qualities of the soil to be preserved, excavating should not be done when the soil is so wet that it will smear or be compacted, but only when it takes considerable pressure to mold a handful of earth. If it's necessary to walk on the bottom of an excavated trench, a plank should be used temporarily. Excavation should be at least 18 inches below grade. The tile must be surrounded with clean gravel, broken brick or crushed rock, which should extend from a depth of at least six inches below the tile to at least two inches above the tile. The pitch of tile lines should be a gradual drop of from two to four inches in 100 feet, and never more than six inches in 100 feet.
     To lay the tile with an even but gradual pitch, a good technique is to set a 1'x4' piece of cheap lumber on edge at the desired level and pitch, to serve as the guide for the tile, then to fill aggregate on both sides of it. The tiles should be placed on the edge of the board, and the latter left in place as aggregate is shoveled in (see Illustration 5). It's important to lay the tiles with a space of 1/4 to 1/2 inch between each pair of adjacent open ends. The upper half of each joint should be covered with waterproof paper (to prevent fine aggregate from silting into the tile). Alternatives to waterproof paper are little half-joint

Figure 7
Illustration 7.


covers of galvanized iron, copper or plastic that are made to achieve equal spacing and alignment. If there are nearby trees and shrubs, trenches should be deeper and wider than usual, with a generous amount of gravel or crushed rock used to minimize the likelihood of moisture retention and thereby discourage root growth in the trench.
     The usual practice is to use untreated building paper, or several inches of straw, hay, pine needles or the like, over the top of the gravel or stone aggregate before backfilling with earth (see Illustration 6). The latter should be hand-tamped (not done mechanically), with the surface at the grade curved to form a convex crown. This surplus earth will serve to take settling into account, as well as to prevent surface water from using the trench as a gutter. The sooner some form of vegetation can form an erosion-resistant mat, the better. It's important to prevent rainwater and surface water from causing premature saturation in the trenches.
     If a disposal field is impractical because of impervious soil, rock formations, limited size of flat area or steep slope of the land, one or more leaching pools, or seepage pits, may be required (see Illustration 7). Often leaching pools are used at the common termination of one or more tile lines, because of insufficient space for the required overall length of the tile lines or because of slow percolation rate or for other reasons. A leaching pool, or seepage pit, is in effect a concentrated disposal field, providing liquids with a means of percolating between adjacent masonry units. Hard-burned bricks, heavyweight concrete blocks or structural clay tiles are laid without mortar, abutting each other, up to the inlet opening (see Illustration 8). Above this level, not only is mortar used, but reinforcing of one kind or another is also used, to prevent cave-ins after torrential rains and other unforeseen conditions.
     The top of the masonry well must be covered with domed courses of masonry and plastered over with cement, or covered with a poured-concrete cap. Whatever the material or construction, there should be a large, removable center plug for inspection purposes. The excavated space between the outside of the well and the exposed soil must be filled with coarse gravel. Since this is the only absorptive material, it should be more than a foot thick. It is preferable to secure the maximum seepage area by building several small pools, rather than a single large one, because (1) it's possible to obtain more square footage of seepage area and (2) there is less likelihood of structural failures or cave-ins in small wells without mortared joints, compared with large-diameter wells.

Figure 8
Illustration 8.


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