The septic tank is a special application container used as the main part of a complete, onsite sewage waste management system. Septic tanks are made for the storage, handling, breakdown and eventual release of human biowaste. Septic tank systems are also known as onsite wastewater treatment, decentralized treatment, cluster systems, on-lot systems, and private sewage systems.
The use of septic tanks and systems is fairly common in North America, and more so in rural areas. According to U.S. federal research and data, anywhere between 20 to 30% of all American households use a septic system to handle human waste. This value is a bit misleading, however, as it considers the entire United States as an average. Some locations have a much higher percentage of septic system use, with some States averaging as much as 40% of residents or more on a septic tank.
Septic tanks are used in residential homes, farms, businesses and industries. In general, septic systems are installed and used whenever the property lacks a connection to municipal provided sewer services. Common reasons for needing a septic tank include local zoning requirements, physical location and distance, and other similar access restrictions all tied to whether a municipal sewer plumbing system is in the area or the cost of connecting to the sewer main.
Septic Systems: Overview
There are numerous septic system types and each has been designed according to location requirements of property size, regular water usage, and underground geological features such as depth of groundwater and makeup of the soil as to whether or not it is conducive to sufficient infiltration of the septic drainage to sustain operation of the system. The specific installation and use of septic tanks and their systems has been standardized and is often overseen by regional guidelines, law codes, and/or permits. Being standardized means each of the different septic system types are built similarly using the same principles each time.
While there are many types of functional and effective septic systems, there are five types that are used most often. Polyethylene plastic septic tanks are fairly new compared to concrete septic tanks but provide many exclusive benefits and advantages and are acceptable for use in each of the different septic systems.
The following 5 septic system types are the ones most frequently chosen whenever a property requires the use of a septic tank.
Gravity Fed Septic Tank Systems (Conventional)
The Gravity Fed Septic System is the most common septic system type, and it is for this reason it is also known as a conventional system. Gravity fed septic systems are also one of the more simple, easier to install, and maintain of the possible system types. If you live in a home on a septic tank, chances are it is a conventional gravity fed septic system.
The gravity fed septic system is so-called because it only uses the natural force of gravity to receive wastes from the property and make the system work. No additional technology or electricity is required for a conventional system. In this system, a decentralized septic tank, (meaning located apart from the structure), receives blackwater and greywater influent from the property through gravity driven flow. The septic tank then connects to a drain field for the distribution and further filtration of the septic tank wastewater effluent.
Conventional septic system drain fields are often underground trenches lined with stone, most commonly gravel, that creates the system’s leach field that is designed to complete waste breakdown through microorganism activity and underground geology. The total number and length of conventional drainage fields will depend on the scenario specifics.
In general, gravity systems require at least 3 feet of conducive subsurface soils beneath drain fields for post-septic tank fluid release and treatment. Conditions such as a high groundwater table, high bedrock layer, and limited land space can make conventional septic tanks unsuitable or impractical for use and can indicate the need for a different system.
Gravity based septic systems can require less regular maintenance or economic input when compared to other frequently used systems. Polyethylene plastic septic tanks make an excellent option for conventional gravity fed septic tank systems.
Chamber Septic Tank Systems (Pressure Distribution, Gravel-less)
The Chamber Septic Tank System, also known as a pressure distribution or a gravel-less system, differs from a conventional gravity system only in the design of the drain field. Gravel-less systems replace stone-lined leach fields with long-channel drainage chambers. These drain chambers are made to fill with wastewater and distribute it to microbial active soils along the bottom of the chamber that further facilitates waste breakdown.
The drain chambers are often made of plastic high density polyethylene but can be and are manufactured from various materials. This septic tank system design type has seen a growing increase in its use as a simple, often lower cost alternative to gravel based systems that is also suitable for areas that experience higher groundwater tables and variable septic influent volumes. Regular maintenance and inspections are similar to those of conventional systems.
Mound Septic Tank Systems
Mound Septic Tank Systems incorporate the use of a man-made mound constructed with distinct layers of soil, gravel and sand that serves as the system’s drainfield. Mound systems are often reserved for property locations that are determined unsuitable for conventional or other common septic tank systems due to substantially shallow soil, shallow groundwater, and/or near-surface bedrock.
In mound systems, septic tanks operate normally under anaerobic conditions but make use of an outflow pump that propels wastewater up against gravity to reach the filtration mound. This differs from conventional systems that make use of gravity to move effluent to the underground leach field. Here, septic effluent is pumped up to the gravel layer of the mound leach field where wastewater then flows from pores in the piping to the underlying sand layer. The man-made sand layer acts as both a soil buffer and filter zone for the microorganism activity required to treat septic system wastewater and effectively prevent harmful waste materials from reaching groundwater or other sensitive environments.
Mound systems need regular maintenance and inspection of all working parts as well as electrical energy input to power the effluent pump. Mound systems require and use the same types of underground septic tanks as conventional septic tank systems.
Recirculating Sand Filter Septic Tank Systems
Recirculating Sand Filter Septic Tank Systems, as the name indicates, uses a sand filter that will treat and recirculate wastewater effluent prior to its subsurface soil release. This septic system type can be constructed above ground or underground and commonly features a concrete or PVC lined box to serve as the sewage breakdown filter for the system. The box filter is often filled with sand that is layered over stone and is conducive to growth of the necessary bacteria.
In this system type, a pump distributes effluent to a filter box where it flows through sand to be collected by pipes in the stone layer. Treated wastewater then returns to the pump for recirculation and further treatment or is pumped downstream out to the soil subsurface. Recirculating sand systems can be used in shallow ground water areas with only 1.5 feet of suitable soil.
Recirculating sand filter systems are often more expensive, require a pump and electricity, and often need more maintenance than the other common and more simple septic tank systems, but still require and make use of an underground septic tank. The low profile septic tank makes a great choice for recirculating sand filter septic tank systems.
Aerobic Treatment Unit (ATU) Septic Tank Systems
Aerobic Treatment Unit (ATU) Septic Tank Systems can be thought of as a small version of municipal, regional sewage treatment plants. The ATU method differs from the other common system types as it uses aerobic microbes versus anaerobic microbes in the breakdown process of incoming biowaste materials within the septic tank. In ATU systems, an electric pump forces air (i.e. oxygen) into the septic tank. This addition of oxygen allows aerobic microbes to flourish inside the sealed, otherwise anaerobic sewage treatment tank, significantly increasing waste breakdown and the resulting quality of the tank effluent.
Aerobic treatment septic systems are frequently chosen for locations and properties that have limited access areas, have nearby surface waters, or soil conditions that are not suitable for conventional septic treatment systems. The ATU system type requires regular maintenance, and some designs may require additional pre-treatment or post-treatment tanks. This style of septic tank sewage management can be the costliest to implement but can provide the best- treated tank effluents of the system types discussed here.
Both standard underground septic tanks and septic pump tanks are commonly used in ATU systems.
Compatible, All-Purpose Septic Tanks
At the end of our review of the five most frequently used septic tank system types, it is our hope there is a better understanding of their features, how they work, and the general specifics involved in septic tank installation.
If looking for the right septic tank capacity that is compatible with your specific property and system requirements, consider our long-term durable, seamless septic tanks fabricated from high density polyethylene. Our industrial-strength, plastic septic tanks have been designed to outlast concrete tanks and remain unaffected by common concerns of cracking, corrosion stress and biowaste degradation. Plastic septic tanks also cost less, are lighter in weight, and easier to install. For any questions, to receive a quote or to place an order, contact us today.