Septic System Design and Maintenance

Save money by getting to know your septic system design and maintenance procedures.
LaNeta R. Crighton
March/April 2011
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This illustration shows the complete septic system, from plumbing vent to septic tank to drain field.
illustration by Nate Skow
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Sometimes, we take things for granted. A hot shower, a load of laundry or a flush of the toilet may be just a routine part of our day, but it can add up to a lot of water down the drain. In fact, the average person uses between 50 and 70 gallons of indoor water each day, and the majority of us don’t give a second thought as to where all that wastewater is headed. Take a little time to understand septic system design, and you're sure to save a bundle of money in the long haul.

More than one-fourth of all homes in America have a septic system, and each one requires maintenance to keep it running properly. With prices for new septic systems ranging from $3,000 to more than $40,000, depending on the type of system and the cost of installation, proper maintenance can mean big savings.

How it works

Since most septic systems are underground and out of sight, they’re easily ignored until things go wrong. Whether you’re installing a brand-new system or you’ve
inherited an older one, becoming familiar with it can save headaches and dollars. Maintenance of a private system is the homeowner’s responsibility. Understanding how it works is the first step in caring for it. Most basic septic systems have three main components:

  • Household wastewater pipe – Each time you turn on a faucet or flush a toilet, wastewater is carried through a pipe and into your septic system. The number of people living in your home and your water usage habits determine the flow going into the system. If a system isn’t designed to handle the volume of wastewater flowing into it, an overload occurs, and that can mean big problems for a homeowner.
  • Septic tank – The size of the tank is determined by house size and water usage. It may also be mandated by state and/or local regulations. The number of bedrooms is a good guide. A three-bedroom house typically requires a 1,000-gallon tank, and it increases 250 gallons for each additional bedroom.
  • Inside the tank, the heavier solid material sinks to the bottom, and fats and grease float on top. The liquid effluent in between flows out to the drain field (or in some older installations, a rock-filled pit called a French drain) through a T-shaped outlet that helps prevent solids from escaping. A screen or filter is required in some states to prevent solids from escaping. The sludge –
    solids that collect in the bottom of the tank – periodically has to be removed by pumping. Some tanks have risers with bolted lids that allow easy access for checking sludge levels without opening the tank.
  • Drain field – An underground pipe carries the liquid effluent from the tank to the drain field, where it’s distributed into a series of shallow trenches lined with gravel and covered with soil, or plastic chambers covered with soil. The soil in the absorption field is loaded with bacteria, which purify the liquid waste before it makes its way into groundwater.
  • The area ideally should be covered with nothing but grass. Tree roots, heavy vehicles or even compaction from excess foot traffic can cause irreparable damage.

Existing systems

Jan Hygnstrom, extension project manager for the University of Nebraska-Lincoln, says some experts believe systems that have been well-designed and maintained can last 30 years or more, but that’s not always the case. Drain fields that have been overloaded, have compacted soil, or that were installed or maintained poorly may have a much shorter life span.

Sometimes it can be difficult to locate the tank and drainage field, especially with older systems that are completely buried. Most county health or building departments keep records showing the exact locations of private septic systems. If you don’t have a drawing of your system, you can try to locate it by finding the wastewater pipe that runs from the house to the tank, usually the largest pipe exiting your house. The tank should be directly in line with the pipe. Use a long metal rod to probe the ground, starting about 10 feet from the house. If you are still unable to locate your system, a professional can help.

Septic experts also can help determine the condition of your system and whether it’s adequate for your home and family. Additions and renovations can cause a home to outgrow its system, since more household members mean an increased wastewater flow. Hygnstrom recommends monitoring wastewater usage over a set period. “Have the tank pumped after a year of use,” she says. “At that point, he (a service person) should be able to recommend a good pumping interval, as long as you have the same water usage.”

David Lindbo, professor of soil science at North Carolina State University in Raleigh, says regular pumping is the most important thing you can to do to keep an existing system in good working order. Once solids fill the lower one-third of the tank, they should be removed. This helps prevent the sludge from overflowing into the drain field.

Many septic owners rely on helpful tips to remind them when it’s time to empty their tank.  “Some people have their tank pumped every time there’s a presidential election,” Lindbo says, “kind of an out-with-the-old, in-with-the-new attitude.” Others pump their tank during years that are divisible by five. Whatever method you choose, the important message is to have your tank pumped regularly.

Owners also should be informed about state and local regulations for septic systems. Lindbo says some states, like his, require routine septic inspections to ensure systems are functioning properly.

Installing a new septic system

Most states make allowances for existing systems, but new systems are sometimes required to meet stringent guidelines. Soil type, lot size and property location all play a role in determining the type of septic system required. Hygnstrom recommends property owners planning new construction first consult a soil expert. “Determining the location of the septic system before choosing the house site could save thousands of dollars,” she says. By selecting an optimal location for the drain field first, it may be possible to avoid the need for complicated routing or expensive alternative systems.

Jeffrey Edwards, a New York- and New Jersey-area septic system contractor, says newly constructed systems are required to meet all codes. In his region, an engineer designs new septic systems based on soil testing and other factors, such as the water table and location of any nearby wells or bodies of water. The process starts with digging a test hole several feet deep, which allows a soil expert to examine several layers of soil. In some states, soil percolation tests are done to determine how fast the soil absorbs moisture. The characteristics of a particular lot and the regulations for the region influence the kind of system required, and the cost.

“It’s hard to give an average when it comes to price. I’d say most systems I do come in at around $10,000,” says Edwards, “but lakefront systems can be $40,000 to install.” Lindbo estimates the average system installation in North Carolina to be around $5,000.

Some states allow new drain field lines to be installed between existing trenches, while others require owners to select an undisturbed area. Sometimes, when the first system is installed, an additional area must be set aside to be used as an alternative drain field if the first one fails. And, some states even require alternating fields. These fields have a valve that can be opened and closed, switching flow from the first field to the second every year, which allows drain fields to rest.

Conventional systems

There are two types of conventional septic systems: gravity and pressure distribution. As the name implies, the gravity system relies on gravity to carry the effluent from the tank to the drain field. When the drain field is higher than the tank, the effluent has to be pumped uphill. Systems where effluent is pumped to the drain field and then distributed by gravity are called pump to standard gravity systems.

In pressure distribution, a pump is used to distribute the effluent all the way to the end of the drainage pipes. This type of system is considered more efficient because the effluent is released at intervals, thus allowing a period of rest for the field. The pressure also helps to push the liquid the full length of the trench and spreads it over a larger area.

“Pressure distribution is used mainly when the drain field is higher than the house, or on odd lots when sewage needs to be moved in a predictable way,” says Lindbo. Smaller lots or those with poor soil may also require this type of system.

Alternative systems

If the site isn’t suitable for a traditional system, an alternative system may be used. These are appropriate for both new and replacement systems, but they’re usually more expensive and require more maintenance than traditional septic systems. Many varieties of alternative systems exist, including the mound system that uses additional soil or sand to raise the drain field, creating a hump or mound. It’s a good choice in areas where the water table is high or soil conditions are poor.

Media filters are another type of nontraditional waste treatment system. They feature a box with materials such as sand or peat. These filter systems pre-treat the effluent and recirculate it before releasing it into the drain field.

Aerobic treatment centers are used as replacement systems when traditional systems are not a viable option. They use oxygen to break down waste, much like a smaller version of a municipal wastewater treatment plant. They can be expensive to operate because they require electricity, and they also may require more maintenance than typical systems. They work for lots with limited space, high water tables or poor soil quality.

Maintaining your system

The No. 1 rule in septic system maintenance is to routinely have your tank pumped by a licensed expert. Once a tank becomes full of sludge, you probably have jeopardized the entire system because there’s a likelihood that solids and scum have escaped into the drain field, which can cause serious damage.

Some septic owners have garbage disposals, but Edwards recommends against them. The additional volume of waste and water usage means more frequent pumping and an increased risk of system clogs. Composting or throwing the scraps to the pigs are good alternatives. Also, refrain from flushing items that don’t break down easily in the toilet. For a list of such items, talk with your local hardware store or a septic system expert.

Most experts agree that additives aren’t really necessary. Studies have shown they provide no real benefit and, in fact, some may actually be harmful. “It’s an old wives’ tale that adding yeast is beneficial to septic systems,” says Lindbo. “Yeast creates gas, which generates bubbles, and actually disturbs settling in the tank. And as far as other additives, they really offer no discernible benefit.”

Even products marketed as “septic safe” may not be advantageous. Hygnstrom says there is no industry standard to determine what this means. Instead, use common sense when it comes to product selection. 

Bottom line: “Treat your system as if it will cost you a lot of money if it’s destroyed,” says Lindbo. “Because the reality is, it will.” 

Proper maintenance of your system is the best way to ensure it will continue working for years to come:

  • Avoid putting anything but human waste and toilet paper into toilet bowls.
  • Limit laundry to one or two loads each day rather than several at one time.
  • Opt for liquid detergent, and use less than the recommended amount.
  • Limit bleach use and avoid toilet bowl hangers that release bleach with flushing.
  • Check for plumbing leaks, which can lead to system overload.
  • Don’t pour grease or cooking oils down the drain.
  • Never pour harsh chemicals like paint thinner, varnish, motor oil or gasoline down the drain.
  • Think twice before installing a garbage disposal, and limit its use if you already have one.
  • Plant only grass over drain field and keep area free of tree and shrub roots.
  • Avoid parking or driving over drain field.
  • Have tank pumped regularly, and treat your system with care

Signs your septic system may be failing:

  • Back-up of floor drains and toilets
  • Plumbing fixtures that take longer to drain than normal
  • Gurgling sounds in plumbing lines
  • Foul smell, particularly after rainfall
  • Mud or pooling of water over drain field
  • Presence of bacteria in your well water

LaNeta Crighton is a New Jersey resident and septic system owner. She has adjusted to life without a garbage disposal or fluffy toilet paper. She also, on occasion, has been accused of pampering her septic system more than she does her husband.


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