Types of Septic Systems

So you need a septic system. Did you know that means you’re going to have to pick a type of system? There’s a wide variety of system types out there, but before diving into the details of every one, the ten in this post (considered the most common by the EPA) are a great place to start.

The type of system best-suited for you will depend on things like your household size, soil type, lot size, surrounding water bodies, and more. Here’s the very basics on both conventional types of septic systems and common alternative systems.

Septic Tank

The septic tank itself is a buried, watertight holding tank built to hold and do light treatment on a household’s wastewater. Solid matter settles to the bottom of the tank while liquids are discharged to treat and disperse in the soil. Read more about the septic tank here >>

Conventional System

The most conventional kinds of systems have a septic tank and a trench or a drainfield for liquids to disperse into. The practice of using gravel or stone for this drainfield goes back decades — the stone filters out larger contaminants and microbes in the soil below further treats the water. These systems have large footprints and won’t suit all residential sites; though they are most commonly installed in single-family homes or small businesses.  

Chamber System

Gravelless systems have begun to replace traditional gravel systems in recent years. There are many forms of gravelless drainfield, and they offer a smaller carbon footprint than a gravel system does. In a common type of gravelless system, chamber systems, a series of chamber pipes carries the wastewater directly from the tank into the soil. These systems are ideal for areas with higher groundwater tables and where the septic usage volume is more variable. Read more about chamber systems >>

Drip Distribution System

This type of system can be used in many kinds of drainfields. The tank discharge is slowly dripped out in a wide reaching array of shallowly-placed lateral pipes. Drip distribution does require electrical power to regulate the timed drip delivery, and therefore require higher costs and more maintenance. Read more about drip distribution >>

Aerobic Treatment Units

ATUs are like a miniature municipal sewage plant. The treatment tank is injected with oxygen to stimulate natural bacterial activity for further treatment., and some can have additional  tanks to perform more disinfection and pathogen reduction processes. These systems work well in smaller lots, poor soil conditions, and areas with a high water table or nearby surface water. Read more about aerobic treatment >>

Mound System

A mound system will require building an artificial sand mound for the wastewater to be pumped into and flow through before reaching the native soil. This works well in places with shallow soil or bedrock and with high water tables. They do require more space and maintenance than the average. Read more about mound systems >>

Recirculating Sand Filter System

This type of system is more expensive than most conventional systems, but performs a high level of nutrient treatment. After leaving the septic tank, the wastewater will flow into a pump tank which pumps it at a low volume through a sand filter contained with PVC or concrete. Then, like a mound system, the water will filter into the native soil. Read more about recirculating sand filters >>

Evapotranspiration System

In this kind of system, the wastewater will never reach the soil or the groundwater. Instead, it evaporates from the drainfield into the air. This is only workable in arid, hot conditions with shallow soil. Read more about evapotranspiration systems >>

Constructed Wetland System

As the name suggests, this type of system imitates the treatment processes of natural wetlands. After leaving the septic tank, pathogens and other nutrients will be filtered from the wastewater by microbes, plants, and other media, before reaching a drainfield. The plants in these systems need to be able to survive in constantly wet conditions. Only artificial wetlands should be used to treat wastewater; real natural wetlands are not a wastewater disposal or treatment option. Read more about constructed wetland systems >>

Cluster/Community System

Essentially, a cluster or community system is a septic system large enough to handle the wastewater of two or more households or buildings. You’re likely to find them in rural subdivisions, and they will be subject to common ownership. Read more about cluster systems >>

More Information:

• Find diagrams of each type of system at EPA Septic.

• Peruse decentralized wastewater technology fact sheets.

• 5 Factors to Consider When Choosing a Septic Tank from Pete’s Outflow Technicians

• 10 Different Types of Septic Systems + How to Choose the Right One from The Original Plumber. See here for additional info on outdated systems and other FAQs.

FAQ: "Do Septic Additives Work?"

Question

Should I use any additives in my septic system?

Answer

The short answer is no. A septic system works best on its own as long as it is maintained and the wastewater going through it is from normal household use. There is a huge market for additives claiming to make it function better or prolonging the life of the system, but research and experts agree, that its best to leave it alone, the bacteria we add naturally work best and don't need any help.

We interviewed a number of well and septic experts, and looked for actual research to support or refute claims of the benefits of additives. We found nothing definitive about the benefits of additives, but a number of things about the potential harm additives can cause, especially some chemical additives.

Two good resources on the subject are from the Purdue Cooperative Extension and the National Environmental Services Center (NESC), both of which are discussed below.  We also talked with 2 private well experts who manage state programs that work directly with well owners. Both said they, and other experts they have discussed this with, agree that there is no evidence to support that additives provide any benefit. They added that there is evidence that some chemical additives can damage the natural bacteria populations in a septic tank or allow solids to get into a septic field. Lastly, we contacted the USEPA, and their response followed suit, “Proper care and maintenance every 3-5 years (pumping the tank to remove solids) is recommended. All additives do is give the homeowner a false sense of security that their system will be fine if they add it.”

When we first answered this question as part of a septic webinar we conducted in the summer of 2015, we received a bunch of emails from homeowners who swear by their additives and some claimed to only pump their tank every 10 or 20 years. One stated that they had never had to pump their septic tank. We were given websites that provided “evidence” of a particular products success, even videos showing how they work. The problem with all of these testimonials are that the conditions of the testing are not the natural conditions in a tank. There was evidence to support these products under actual conditions in a septic system. These folks are likely in for a surprise at some point when their septic system fails and they either have septic effluent pooling in their backyard, or worse, backing up into their home. Also consider that in some cases the money spent on additives over a 3-5 year period would have likely paid for pumping and inspecting their tank.

Additional Resources

Purdue Extension - This handout does a great job of giving an overview of what the functions of a septic system are and how additives might affect it. It describes the types of additives that are out there, and how their use might impact a septic tank. They recommend good “habits” for how to improve performance of a septic system, by reducing the chemicals used every day that might harm the bacteria in a septic system, and best practices for reducing the amount of flow going through a system.  Improving daily habits can go a long way at preserving the proper function of a septic system.

NESC’s Small Flows Clearinghouse and Magazine - The National Environmental Services Center at West Virginia University has a national technical assistance hotline. The article at the link above was developed from calls they received from homeowners asking about additives for their septic systems. They describe some of the findings from several research studies on additives, but the question we are interested in, “Do I need to use additives…” is the last section on the 2^nd page. My favorite statement, “Contrary to popular belief, yeast, dead chickens, possums, or raw hamburger do not need to be added to the septic tank”, pretty much sums up the folklore and home remedies that have made their way into this conversation.

Note: Hideyuki Terashima at the Illinois State Water Survey did all of the legwork to find and put together the resources used here on this topic. We originally used this information as part of a webinar on septic system issues in May 2015. As part of that webinar, we had a licensed septic installer and inspector participate in answering well owner questions.