What Happens After You Flush: A Guide to Septic Systems

The idea of septic systems may conjure up images of muddy, foul-smelling yards and clogged drains. Yet, a house with a properly installed and maintained septic system won’t appear very different from one connected to a sewer. Approximately 25% of Americans use stand-alone septic systems—as opposed to tying into a city sewer system—to effectively treat wastewater, and they are often the only option in rural areas. They are inexpensive to maintain but do require vigilance to ensure that they don’t become the source of a problem.

Septic Systems Components

Standard septic systems consist of a tank, drain field, and the surrounding soil. The main sewer line carries all the wastewater out of the house and brings it to the underground tank—a 1,000-1,200-gallon watertight chamber made of concrete, fiberglass or polyethylene. Perforated pipes covered in gravel compose the drain field, while the soil underneath is responsible for the majority of the wastewater treatment.

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How Septic Systems Work

The tank will hold the wastewater for one or two days, allowing the heavier solids to sink to the bottom and forming the sludge layer, while fats, oils and grease float to the surface to become the scum layer. Bacteria in the tank will begin to break down the solids, but won’t completely remove them.

The outflow pipe from the tank into the drain field is designed to draw water from the middle section, avoiding both the scum and sludge layers. After exiting the tank, water enters the drain field where it can slowly seep through the gravel into the soil for final treatment. The soil naturally filters, retains or breaks down organic matter, phosphorous, metals, bacteria and viruses. This treated water can then safely be taken up by plants, evaporate from the soil or enter the groundwater.

Septic Systems Maintenance

Maintaining septic systems involves regular tank inspections, pumping when necessary and controlling what enters the system. Specific recommendations include:

• Tanks should be inspected every three to seven years, depending on tank size and number of people.
• Refer to Table 1 in the publication from The NC State Extension Publications for more detailed recommendations on this time frame.
• Pumping the tank prevents excess solid material from escaping into the drain field and creating a clog that could back up the entire system.
• Septic-tank treatment products claiming to break down material in the tank are generally regarded as unnecessary.
• Limit the amount of solid material entering the system by eliminating the use of garbage disposals and not flushing cat litter, solid hygiene products, diapers, coffee grounds or cooking grease.
• Protect the population of helpful bacteria in the tank by limiting the use of bleach, lye, and chemical drain cleaners, and avoid disposing of paint, antifreeze, and gasoline down the drain.
• Avoid using large amounts of water in short periods of time by spacing out laundry wash loads, dishwasher operation and showers. Too much water at once could saturate the drain field and soil,
• preventing adequate treatment.
• Keep trees and large plants away from the drain field.
• Don’t drive or park vehicles on the drain field.
• Keep excess water from the drain field by diverting downspouts and sump pumps away from it.

Where They Can Be Used

The ideal location for a septic system is a gentle slope with a thick layer of permeable soil and a deep water table. Of course, they are used in areas without all these conditions; they just take more work to install. Some basic considerations:

• Systems should be at least 100 feet from wells.
• Each acre of land should have no more than two systems to meet the EPA’s standards for wastewater treatment. Thus they are not options for densely populated areas.
• Soil must not be too rocky or have too much sand or clay.
• Avoid wet, swampy or flood-prone locations.

Your local cooperative extension office can provide information about the soil in your area and if it is appropriate for a septic system. The local health department is usually responsible for issuing permits for the building of a new system.

Septic Systems Costs

The price of a septic system depends on the size of the tank needed and the conditions of the land that affect installation expense. For a typical three-bedroom house, the cost will range between $1,500 and $4,000 for materials and installation. The tradeoff is that once installed, the only additional expense is that of inspections and pumping the tank, which should set you back just $75-150 every three to seven years.

Septic vs. Sewer

According to the EPA, “When septic systems are properly designed, constructed and maintained, they effectively reduce or eliminate most health or environmental threats posed by pollutants in household wastewater.” A limitation of septic systems is that they do not remove all nitrates from the waste, which could cause health problems if they reach drinking water supplies, or environmental issues if they reach surface water sources. One benefit of septic over sewer systems is that treated water helps recharge local aquifers instead of being released into distant water sources.

A major concern with septic systems is that they rely on the homeowner to detect and fix any problems that could lead to untreated wastewater contaminating either the groundwater or surface water sources. A publication (PDF) from The University of Georgia Cooperative Extension estimates that 10-20% of all septic systems in the US are not functioning properly. Laws such as the one proposed in Florida requiring homeowners to have their septic systems inspected at regular intervals would make them more environmentally sound.

The main work for septic-system owners is to ensure that they are designed and installed properly. Subsequently, the systems are inexpensive to maintain and mostly require just regular inspections and common-sense practices about what goes down the drain—measures that should be followed by everyone, even those connected to city sewers. While the location may dictate the wastewater treatment method, septic tanks are an effective option as long as homeowners are conscientious and monitor their systems.

Additional Resources

• EPA’s Checklist for Septic Systems (pdf)
• Septic-Tank Costs
• A Homeowner’s Guide to Septic Systems (pdf)