How a Septic System Works

A septic system is composed of two main components: a septic tank and an absorption area.  Each has an integral function in the treatment and disposal of domestic wastewater resulting from laundry and bathing, kitchen wastes and body wastes.  This relatively simple system of wastewater renovation can effectively remove disease-causing pathogens and chemical nutrients from domestic wastewater for the life of the home when it is properly designed, constructed, operated and maintained.

The Septic Tank

Septic tanks are required to be large enough to hold the sewage for approximately two days before it is discharged to the absorption area.  For a single-family home with at least four bedrooms, the septic tank has to be at least 1,000 gallons in capacity.  Add an additional 250 gallons of capacity for each bedroom over four.

Sewage, which enters the septic tank, is retained for a short period of time, during which it breaks down into scum, sludge and liquid effluent.  Most solid matter will settle to the bottom as sludge while buoyant grease, fats and hair will float to the surface and form a scum layer.  Between these two layers is the clear effluent, which drains into the absorption area.  The solids in the septic tank will be digested and converted into gases by microorganisms such as bacteria.

The Absorption Area

Wastewater from the septic tank is passed on to the absorption area, also known as the drain field or leach field.  The absorption area is a series of underground, perforated pipes, which overlay a bed of gravel approximately 12 inches in thickness.  The perforated pipes, which are in individual trenches or grouped together into a single bed, distribute the wastewater throughout the entire area of the absorption area.

Near the bottom of the gravel bed of the absorption area, a slimy mass accumulates known as the biological clogging mat or biocrust.  This biological layer, which occurs naturally in all properly designed, constructed and operated septic systems, consists of wastewater solids, microorganisms and the by-products of decomposition.  The biological clogging layer represents a treatment medium for applied effluent in which larger microorganisms, such as bacteria, are filtered out along with suspended solids.  Additionally, due to its reduced permeability, the biological clogging layer slows infiltration into the soil, and as such, equilibrates effluent throughout the entire absorption area.  Within the soil, smaller microorganisms such as viruses become immobilized upon soil particles and die, while wastewater nutrients such as phosphorus and some forms of nitrogen are absorbed and become bound within the soil.

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Recommended Operation and Maintenance Practices

Septic system owners are unique in that unlike areas served by regional sewerage systems, the septic system owner is solely responsible for the daily operation and maintenance of the wastewater treatment and disposal system.  By adhering to simple and straightforward guidelines, the septic system owner can ensure years of trouble-free operation with a minimal degree of maintenance.

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Septic System Operation

• DO try to distribute dish washing and laundry throughout the week rather than all at once during one or two days.

• DO avoid showering and bathing at times when dishwashers and laundry are in use.

• DON’T pour cooking oils, fats or grease into the kitchen sink.  These items congeal in either the internal home plumbing or the septic tank, which will result in premature maintenance on these items.

• DON’T flush inert or non-biodegradable items down sinks or toilets.  Items such as disposable diapers, cat litter, cigarette filters, sanitary napkins, paper towels, condoms or similar materials may result in clogging of the plumbing and will result in the need to prematurely pump the septic tank.

• DON’T flush toxic substances down sinks or toilets.  Introduction of substances such as waste motor oil, oil-based or acrylic paints, varnishes, photographic solutions, pesticides, insecticides, paint thinners, and organic solvents and degreasers into a septic system not only compromises its performance, but also contributes to ground water pollution.

• DON’T plant trees or other vegetation with extensive and deep root systems.  Tree roots are capable of exerting enough pressure to rupture or dislodge distribution boxes, connecting pipes, manifolds and laterals.  Grass is the best vegetative cover for absorption areas.  It has a great capacity to consume water and does not have a woody root system, which can physically disrupt the absorption area.

• DON’T divert surface water runoff towards the absorption area.  The increased volume of water infiltrating into the absorption area can result in hydraulic overloading and ultimately septic system malfunction.

• DON’T construct driveways, parking lots, accessory buildings, additions to the main building, decks or patios, which encroach upon any component of the septic system.  The presence of any of the above in immediate proximity to a septic system may adversely affect the functioning of the system or interfere with system maintenance.

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If Your Septic System Fails

The homeowner with a septic system must not only be vigilant in how they operate and maintain their septic system, but must also be cognizant of indications of impending septic system failure. 

If you recognize indications of septic system failure, you should contact your local health department prior to taking any action to ascertain possible corrective measures and the need for approvals or permits.

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Information and Illustrations from: A Homeowner’s Manual for Septic Systems, published by the New Jersey Department of Environmental Protection.