A Choice of Simple, Safe Disposal Systems

Even small amounts of refuse and waste water from a cabin or cottage must be disposed of with care—and by the method appropriate to the material. You must cope with a variety of different materials: the solid debris of day-to-day living, the liquids that drain from a sink, and the wastes of a toilet.

Many vacationers burn solid waste such as trash or garbage, or bury it in a remote trench. Others can dispose of their refuse at a local dump, and still others take it home in a plastic bag for pickup by a trash-collection service.

Waste water from a sink presents a different disposal problem. In all but the most remote regions, sanitary codes generally forbid the old-time practice of simply sloshing the contents of a wash basin on a handy patch of ground—and with good reason. Wash water is frequently high in phosphorus and grease, and may contain food particles, bacteria and viruses—substances that can pose a health hazard if they are not conducted safely away from dwelling places.

Before you design your own water- disposal system, consult local health officials, who will tell you the kind of system required in your locality. Some sanitary codes call for a full-scale septic system, of the kind that's used with a flush toilet; others accept the smaller installations and simpler methods shown.

Any system you install must include a pretreatment tank, or grease trap, in which solids settle to the bottom and pipe-clogging greases float to the top be fore the water is dispersed by absorption or evaporation. Locate the trap at least 50’ from the nearest well or stream, and at least 10’ from both the cabin and the property line.

If you dispose of less than 10 gallons of water a day, a 30-gallon plastic garbage can makes an ideal grease trap. For disposal loads between 10 and 50 gallons daily, use a precast concrete distribution box in addition to the grease trap; the box supplements the action of the trap, and also routes water to a larger absorption or evaporation area. Larger volumes of waste water require the use of a septic tank.

After passing through a trap or tank, waste water is piped away for final disposal, generally by absorption into the ground, which can soak up and filter waste water until the soil is saturated or, in technical language, overloaded. To determine whether overloading is likely in your area and under your disposal load, you must know the soil’s capacity to absorb liquids. In many areas, suitable soils can be identified with the help of U.S. Department of Agriculture maps and re ports, and the advice of the USDA extension service. Elsewhere, examination of the soil provides clues: as a rule, the best soils for drainage and absorption are light and sandy, and break apart easily into clods of uniform shape and size.

The final step in gauging the drainage characteristics of a soil is a percolation test, which in many areas must be per formed by a sanitary engineer. The tester digs several holes on the site, fills the holes with water and measures the time it takes for the water to drop 1”. In general, the percolation rate for an absorption trench should not be more than 60 minutes per inch, though local authorities set their own standards.

In deciding upon the type of disposal system you must have, health officials consider the size and shape of the disposal area, the topography of nearby land, the amount of water to be handled and the percolation-test results. If waste- water volume is fairly light and the drain age capacity of the soil is good, you may get approval to build a simple seepage or an underground disposal bed. An evapo-transpiration bed may be permitted in areas of high temperature, low humidity and poor drainage.

Four Basic Systems

116 A seepage pit. The simple stone-filled pit at right, which contains waste water until the water is slowly absorbed into the surrounding soil, is adequate for low-volume water treatment. Waste water flows down from the cottage in a 2” pipe and enters a small grease trap—in this example, a 30-gallon plastic garbage can. Solids settle to the bottom of the trap, congealed grease rises to the top, and the relatively clear waste water trickles through a pipe into a pit 4 to 7’ deep.

The pit is filled with irregularly shaped rocks and topped with a mound of dirt; a 1-to 2” layer of straw or hay between the dirt mound and the rocks below it prevents earth from sifting into the spaces between rocks.

117 A network of underground pipes. In this disposal-bed system, waste water is distributed evenly through perforated pipes to the surrounding soil.

From a garbage-can grease trap, the waste water flows into a concrete distribution box, where its velocity is slowed by an internal baffle or wall in the box; the water is then channeled equally to 4- inch perforated pipes. Both the distribution box and the pipes are set level in a bed (at least 10” thick) of stones ¾ to 3” in diameter. Cover the pipes with at least 2” of stones, then add a 2” layer of hay or straw and an 8- inch mounded topping of soil.

117b An evapo-transpiration bed. Between 1½ and 3 feet deep, this bed is lined with 10-mil plastic, to prevent water from seeping into the soil, and filled with fine sand. Waste water runs from a grease trap into a 2-inch perforated pipe that extends to the middle of the excavated bed; the pipe is surrounded by stones to prevent sand from blocking its perforations. Heavy waterproof tape is used to seal the area where the pipe enters the plastic liner. A bed that's used only during the summer can be seeded with alfalfa to speed the evaporation process. For the winter months, when periods of sunshine are brief, no vegetation should be planted.

118a Septic tank with absorption trenches. Waste water flows through an underground pipe to the septic tank, where solids sink to the bottom, oils and grease float to the top, and gas escapes back through the inlet pipe to the house drain vent. The remaining liquid, which is called the effluent, flows slowly through the outlet pipe and out into a drainage field.

In this example, the drainage field consists of a closed loop of perforated pipes that releases the effluent downward and outward into the surrounding soil. The pipes are laid in level trenches, which may be 10 to 36” wide, 2 or more feet deep and 6 to 10’ apart. They rest on at least 6” of stone, and are topped with 2 or more inches of stone, 2” of straw or hay and 4 to 6” of soil.

Connections to a Trap, Tank and Box

118b Making a grease trap. On opposite sides of a 30-gallon plastic garbage can, just below the rim, cut holes slightly smaller than the inlet and outlet pipes, with the inlet hole at least 1” higher than the outlet hole. Set the can in a level pit and pack the space around it with dirt up to the bottoms of the holes; dig trenches from the cabin to the inlet hole and from the outlet hole to a seepage or distribution box. Force the inlet pipe through the inlet hole, seal the hole around the pipe with silicone caulking and attach a 90-deg elbow, pointing downward, to the inner end of the pipe. Insert and seal the outlet pipe; at its inner end, attach a fitting called a sanitary T, connected to a pipe that ends at least 5” above the bottom of the can.

Set the garbage-can cover in place, pack the remaining space around the sides and conceal the can with a wooden cover. Inspect the trap periodically; remove large accumulations of grease and solids with a shovel and bury them.

Sealing a box or a tank. In disposal systems containing a septic tank or (as in this example) a distribution box, seal around the inlet and out let pipes with mortar. Set the outlet pipes at the same level and the inlet pipe at least an inch higher to prevent the system from backing up (some codes require a septic tank inlet pipe to be 3” higher than the outlet pipe). Then fill the spaces around the pipes inside and out side the box with chips of brick and apply a mortar of 60 per cent cement and 40 per cent sand.