Septic System: Types, Cost, and Diagram

What is Septic System?

Septic systems are underground wastewater treatment structures, commonly used in rural areas without centralized sewer systems. The septic tank digests organic matter and separates floatable matter (e.g., oils and grease) and solids from the wastewater.

They use a combination of nature and proven technology to treat wastewater from household plumbing produced by bathrooms, kitchen drains, and laundry. A typical septic system consists of a septic tank and a drain field, or soil absorption field.

Soil-based systems discharge the liquid (known as effluent) from the septic tank into a series of perforated pipes buried in a leach field, chambers, or other special units designed to slowly release the effluent into the soil.

Alternative systems use pumps or gravity to help septic tank effluent trickle through sand, organic matter (e.g., peat and sawdust), constructed wetlands, or other media to remove or neutralize pollutants like disease-causing pathogens, nitrogen, phosphorus, and other contaminants.

Some alternative systems are designed to evaporate wastewater or disinfect it before it is discharged to the soil.

Septic System

Common Parts of a Septic System

A septic system is not necessarily a complex system and each of its components work together to make sure your household’s waste is properly stored and disposed of.

1. Septic Tank


The septic tank is a large rectangular or cylindrical container made of concrete, fiberglass or polyethylene that is buried under the ground on your property.

These onsite sewage facilities are used for properties that are not connected to a sewer system and are most commonly found in rural areas.

2. Drain field

Sewage from the septic tank flows through pipes into your yard through the drain field. Wastewater is typically stored in the septic tank for two days before being released to the drain field.

This part of your septic system involves long pieces of pipe, called “drainpipes”, that feature small holes that allow for this release.

Drain fields can become potentially blocked if solids build up and are not pumped out properly. These blockages can be caused by an undersized septic tank, infrequent pumping of the septic tank, and high volumes of water.

Your drain field may be blocked if you notice:

  • Greener grass over the drain field
  • Strange odors in your yard
  • Plumbing backups
  • Wet or mushy ground

If your drain field is blocked, your entire septic system will not function properly. It is best to call in professional underground service technicians to alleviate the issue.

3. Pump Tanks

While pump tanks are not a necessary component of your septic system, they are recommended to ensure the proper operation and maintenance of the system.

Pump tanks contain the following:

  • Effluent pump. Catches solids before they leave the tank to prevent them from being released into the drain field to prevent clogging of the drain field.
  • Control floats. Connected to a control panel and signal when to turn the pump off and on
  • High-water alarm. Activates if the pump fails to work to indicate high volume in the septic tank. Typically located under the kitchen sink or in the garage.

If the high-water alarm is activated, it is best for homeowners to conserve water and have an expert septic system technician to inspect the water levels.

4. Distribution Box

The distribution box is located between the septic tank and the drain field and is designed to evenly distribute wastewater equally between the drain field lines.

5. Leach Drain Field

The leach field, or septic field, is a part of your septic system that receives the effluent from the septic tank. It refers to the network of drainpipes, stones, and a layer of unsaturated soil. It distributes waste into the soil which then eventually returns to the water table.

Septic System Diagram


How Septic System Works?

Specifically, this is how a typical conventional septic system works:

  1. All water runs out of your house from one main drainage pipe into a septic tank.
  2. The septic tank is a buried, water-tight container usually made of concrete, fiberglass, or polyethylene. Its job is to hold the wastewater long enough to allow solids to settle down to the bottom forming sludge, while the oil and grease float to the top as scum.
  3. Compartments and a T-shaped outlet prevent the sludge and scum from leaving the tank and traveling into the drain field area.
  4. The liquid wastewater (effluent) then exits the tank into the drain field.
  5. The drain field is a shallow, covered, excavation made in unsaturated soil. Pretreated wastewater is discharged through piping onto porous surfaces that allow wastewater to filter through the soil. The soil accepts, treats, and disperses wastewater as it percolates through the soil, ultimately discharging to groundwater.
  6. If the drain field is overloaded with too much liquid, it can flood, causing sewage to flow to the ground surface or create backups in toilets and sinks.
  7. Finally, the wastewater percolates into the soil, naturally removing harmful coliform bacteria, viruses and nutrients. Coliform bacteria are a group of bacteria predominantly inhabiting the intestines of humans or other warm-blooded animals. It is an indicator of human fecal contamination.

What Size Septic Tank Do You Need?

Septic tank size is typically determined by the number of bedrooms your home has. This is used as a way to estimate how much water will flow through the system daily. Generally, the larger the system, the higher the cost.

  • Two Bedrooms: A two-bedroom house requires a septic system with a minimum of a 750-gallon septic tank. However, in many municipalities, a 1,000-gallon tank is the smallest size allowed.
  • Three Bedrooms: A three-bedroom house will need a minimum of a 1,000-gallon water tank, which regularly handles about 360 gallons of water per day.
  • Four Bedrooms: A four-bedroom home requires a larger tank with a minimum volume of 1,250 gallons. It handles around 480 to 600 gallons of water per day.

Types of Septic Systems

Septic system design and size can vary widely, from within your neighborhood to across the country, due to a combination of factors. These factors include household size, soil type, site slope, lot size, proximity to sensitive water bodies, weather conditions, or even local regulations.

Below are ten of the most common types of septic systems used. The list is not all-inclusive; there are many other types of septic systems.

  • Septic Tank
  • Conventional System
  • Chamber System
  • Drip Distribution System
  • Aerobic Treatment Unit
  • Mound Systems
  • Recirculating Sand Filter System
  • Evapotranspiration System
  • Constructed Wetland System
  • Cluster/Community System

Septic Tank

A buried, watertight tank designated and constructed to receive and partially treat raw domestic sanitary wastewater. Heavy solids settle to the bottom of the tank while greases and lighter solids float to the top. The solids stay in the tank while the wastewater is discharged to the drain field for further treatment and dispersal.

Conventional System

A decentralized wastewater treatment system consisting of a septic tank and a trench or bed subsurface wastewater infiltration system (drain field). A conventional septic system is typically installed at a single-family home or small business.

The gravel/stone drain field is a design that has existed for decades. The name refers to the construction of the drain field. With this design, effluent is piped from the septic tank to a shallow underground trench of stone or gravel. A geofabric or similar material is then placed on top of the trench so sand, dirt, and other contaminants do not enter the clean stone.

Effluent filters through the stone and is then further treated by microbes once it reaches the soil below the gravel/stone trench.

Gravel/stone systems are relatively large in the overall footprint and may not be suitable for all residential sites or conditions.

These systems cost between $2,000 and $5,000 to install.

Chamber System

Gravel less drain fields have been widely used for over 30 years in many states and have become a conventional technology replacing gravel systems. They take many forms, including open-bottom chambers, fabric-wrapped pipes, and synthetic materials such as expanded polystyrene media. The gravel less systems can be manufactured with recycled materials and offer significant savings in carbon footprint.

An example of a gravel less system is the chamber system. The chamber system serves as an alternative design to the gravel/stone system. The primary advantage of the chamber system is increased ease of delivery and construction.

They are also well suited to areas with high groundwater tables, where the volume of influent to the septic system is variable (e.g., at a vacation home or seasonal inn), in an area where gravel is scarce, or in areas where other technologies such as plastic chambers are readily available.

This type of system consists of a series of connected chambers. The area around and above the chambers is filled with soil. Pipes carry wastewater from the septic tank to the chambers. In the chambers, the wastewater comes into contact with the soil. Microbes on or near the soil treat the effluent.

They cost $1,500 to $5,000 to install.

Drip Distribution System

The drip distribution system is a type of effluent dispersal that can be used in many types of drain fields. The main advantage of the drip distribution system is that no large mound of soil is needed as the drip laterals are inserted into the top 6 to 12 inches of soil.

The disadvantage of the drip distribution system is that it requires a large dose tank after the septic tank to accommodate the timed dose delivery of wastewater to the drip absorption area.

Additional components, such as electrical power, are necessary for this system, requiring an added expense and increased maintenance.

Aerobic Treatment Unit

Aerobic Treatment Units (ATUs) use many of the same processes as a municipal sewage plant, but on a smaller scale. An aerobic system injects oxygen into the treatment tank.

The additional oxygen increases natural bacterial activity within the system which then provides additional treatment for nutrients in the effluent. Some aerobic systems may also have a pretreatment tank and a final treatment tank including disinfection to further reduce pathogen levels.

The benefits of this system are that it can be used in homes with smaller lots, inadequate soil conditions, in areas where the water table is too high, or for homes close to a surface water body sensitive to contamination by nutrients contained in wastewater effluent. Regular lifetime maintenance should be expected for ATUs.

Aerobic systems are more expensive to install. Expect to pay between $10,000 and $20,000.

Mound Systems

Mound systems are an option in areas of shallow soil depth, high groundwater, or shallow bedrock. The constructed sand mound contains a drain field trench. Effluent from the septic tank flows to a pump chamber where it is pumped to the mound in prescribed doses.

Treatment of the effluent occurs as it discharges to the trench and filters through the sand, and then disperses into the native soil.

While mound systems can be a good solution for certain soil conditions, they require a substantial amount of space and periodic maintenance.

They’re also expensive to install because a sand mound has to be constructed. Total cost ranges from $10,000 to $20,000.

Recirculating Sand Filter System

Sand filter systems can be constructed above or below ground. Effluent flows from the septic tank to a pump chamber. It is then pumped to the sand filter. The sand filter is often PVC-lined or a concrete box filled with sand material.

Effluent is pumped under low pressure through the pipes at the top of the filter. The effluent leaves the pipes and is treated as it filters through the sand. The treated wastewater is then discharged to the drain field.

Sand filters provide a high level of treatment for nutrients and are good for sites with high water tables or that are close to water bodies, but they are more expensive than a conventional septic system.

Evapotranspiration System

Evapotranspiration systems have unique drain fields. The base of the evapotranspiration system drain field is lined with a watertight material. After the effluent enters the drain field, it evaporates into the air. Unlike other septic system designs, the effluent never filters to the soil and never reaches groundwater.

Evapotranspiration systems are only useful in specific environmental conditions. The climate must be arid and have adequate heat and sunlight. These systems work well in shallow soil; however, they are at risk of failure if it rains or snows too much.

Constructed Wetland System

A constructed wetland mimics the treatment processes that occur in natural wetlands. Wastewater flows from the septic tank and enters the wetland cell. The wastewater then passes through the media and is treated by microbes, plants, and other media that remove pathogens and nutrients.

The wetland cell typically consists of an impermeable liner, and gravel and sand fill, along with the appropriate wetland plants, which must be able to survive in a perpetually saturated environment.

A wetland system can work via either gravity flow or pressure distribution. As wastewater flows through the wetland, it may exit the wetland and flow into a drain field for further wastewater treatment into the soil.

Cluster/Community System

A decentralized wastewater treatment system under some form of common ownership that collects wastewater from two or more dwellings or buildings and conveys it to a treatment and dispersal system located on a suitable site near the dwellings or buildings. It is common to find cluster systems in places like rural subdivisions.

How Much Does a Septic Tank System Cost?

Septic Tank Costs at a Glance

  • Total cost: $3,900, average; $1,500-$5,000, range
  • Anaerobic septic tank: $2,000-$5,000
  • Aerobic septic tank: $10,000-$20,000
  • Gravity septic tank: $1,500-$4,000
  • Mound septic tank: $10,000-$20,000
  • Chamber septic tank: $1,500-$5,000
  • Conventional septic tank: $2,000-$5,000

The wastewater your household creates is full of dangerous bacteria. Having a fully functioning septic tank is essential to help dispose of it safely and to keep it from backing up into your sinks and toilets.

How Much Does It Cost to Install a Septic Tank?

On average, the cost of installing a new septic tank system is $3,900. The price ranges from $1,500 to $5,000 for a typical 1,250-gallon tank, which is an ideal size for a three- or four-bedroom home.

This cost is inclusive of the tank itself, which costs $600 to $2,100 or more, depending on the type. Labor costs are also included in the installation price and usually range from $1,500 to $4,000.

Signs of Septic System Failure

  • Water and sewage from toilets, drains, and sinks are backing up into the home.
  • Bathtubs, showers, and sinks drain very slowly.
  • Gurgling sounds in the plumbing system.
  • Standing water or damp spots near the septic tank or drain field.
  • Bad odors around the septic tank or drain field.
  • Bright green, spongy lush grass over the septic tank or drain field, even during dry weather.
  • Algal blooms in nearby ponds or lakes.
  • High levels of nitrates or coliform bacteria in water wells.

Like most components of your home, septic systems require routine maintenance. If maintained, the septic system should provide reliable service for many years.

If the septic system isn’t maintained, owners run the risk of dangerous and costly failures. And, septic systems do have an operational lifetime and will eventually need to be replaced.

A failed or malfunctioning septic system is a risk to human and animal health and can pollute the environment.

A responsible septic owner is alert to the signs of failure, regardless of the age of the system, and responds quickly when any are discovered. A quick response may save the owner money in repairs and may prevent illness and negative impact on the environment.

What happens when a septic system fails?

A septic system failure causes untreated sewage to be released and transported to where it shouldn’t be. This may cause sewage to come to the surface of the ground around the tank or the drain field or to back up in pipes in the building.

The sewage could also find its way into groundwater, surface water, or marine water without us ever seeing it. The sewage carries pathogens and other dangerous contaminants. Exposure to these pathogens and contaminants can make people and animals sick.

They can also contaminate water sources and make them unsafe for drinking, swimming, shellfish harvesting, and agricultural uses.

What are some common reasons a septic system doesn’t work properly?

1. Pipe from the house to the tank is clogged.

When this happens, drains drain very slowly (perhaps slower on lower levels of the building) or stop draining completely. This is often an easy problem to fix. Usually, a service provider can “snake the line” and get it unclogged.

You can prevent a clogged line by flushing only human waste and toilet paper down the drain and having your system inspected annually.

Sometimes this pipe gets crushed or broken by vehicle or animal traffic. Plant roots sometimes block the pipe. Fixing a crushed or root-damaged pipe will require replacing (at least) a portion of the pipe.

2. Inlet baffle to tank is blocked.

This failure is very similar to when the inlet pipe from the house to the tank is clogged. If you have access to your inlet baffle opening, you can check to see if there is a clog.

If you see toilet paper and other debris, you can try unclogging it using a pole. Be mindful not to damage any of the septic systems components.

A service professional can also be contacted for this relatively easy and low-cost fix. Prevent your inlet baffle from getting clogged by only flushing human waste and toilet paper and having your system inspected annually.     

3. Outlet baffle or effluent filter is clogged.

This may result in sewage backing up into the home, or possibly surfacing near the septic tank. This issue may be a sign that the tank is receiving too much water, possibly in a short amount of time. If there is an effluent filter this must be cleaned off or replaced.

If there is not an effluent filter, fixing this issue will probably require getting the tank pumped to identify and remove the clog. Prevent this type of issue by cleaning your effluent filter (if you have one) and having your system inspected annually.

4. Drain field has failed.

When the drain field fails or is saturated with water, sewage may back up into the home. Wet, soggy areas may develop above or near the drain field and you may see spongy bright green grass over the area. There may also be odors near the tank or drain field. This could be the end of life for this component of your septic system.

It may be that the system was operated inappropriately and too much solid material made it to the drain field causing it to fail prematurely. Or, maybe the system worked for many years and simply has no more capacity to accept waste.

However, if too much water has saturated the drain field, it’s possible that the drain field can be dried out and rehabilitated. Contact a service professional to assess the situation.

If the drain field has failed, a connection to the public sewer system should be considered, if it’s a possibility. Otherwise, a replacement drain field will need to be installed.

How can I prevent failure?

Routine maintenance and proper operation will help your septic system have a long and trouble-free life. If your septic system has been properly designed, sited, and installed, the rest is up to you.

Inspect your system annually and pump as needed (usually every 3-5 years). Avoid excess water use, and watch what you put down the drain and flush down the toilet.

Can my failing septic system contaminate the water?

Yes, a failing septic system can contaminate well water and nearby water bodies. Untreated wastewater is a health hazard and can cause many human diseases.

Once this untreated wastewater enters the groundwater, you and your neighbor’s wells can be contaminated. If the sewage reaches nearby streams or water bodies, shellfish beds and recreational swimming areas can be contaminated.