Types of septic systems, explained

"Septic system" covers a whole family of designs. They all start with a tank, but what happens after the tank depends on the soil, the slope, the water table, and local rules. Knowing which type you have tells you how often it needs attention and what can go wrong. Your permit or the county health department's file usually names the type.

Conventional systems

A conventional system is a septic tank plus a gravel or stone trench drainfield. Effluent flows from the tank into perforated pipe laid in gravel, and the gravel and soil treat and absorb it. EPA notes these are typically used for single-family homes and small businesses. They need a fair amount of space and suitable soil.

A chamber system swaps the gravel for open-bottomed plastic chambers. EPA describes them as easy to build and a good choice where gravel is scarce. They work the same way underground, and some designs can use gravity or a pump.

Systems for difficult sites

Mound systems are used where the soil is shallow, the groundwater is high, or bedrock is close to the surface. The drainfield is built above ground in a sand mound. A pump chamber doses effluent into the mound in batches. They take up space and have a pump to maintain.

Recirculating sand filters pass effluent through a lined sand filter box, often more than once, before it goes to the drainfield. EPA says they can give a high level of nutrient treatment and suit sites with high water tables or near water bodies. They cost more than a conventional system.

Drip distribution systems use small tubing laid just under the surface to spread effluent across a large area. They need a dosing tank, a pump, and timers, so they need electricity and regular maintenance.

Aerobic treatment units (ATUs) work like a miniature municipal plant. They inject oxygen so bacteria break waste down faster and more completely. EPA notes they're useful where soils are unsuitable, groundwater is high, or a home is near surface water. They need lifetime maintenance and electricity.

Less common types

EPA's list also includes evapotranspiration systems for arid climates, constructed wetlands that treat effluent in a planted cell, and cluster or community systems where several homes share treatment. Rules for these vary a lot by state.

Why the type matters for maintenance

EPA's care guidance says a typical household system should be inspected at least every three years. Alternative systems with electrical float switches, pumps, or mechanical parts should be inspected more often, generally once a year. Many states require a service contract for aerobic units. Anything with a pump has an alarm. Learn what it sounds like, and don't just silence it. Call a service provider.

The tank still needs pumping whatever type you have. Our pumping calculator works for the tank in any system. For systems with a pump chamber, ask your provider whether that chamber also needs pumping or cleaning.

If you're not sure what you have

Look for clues: a raised mound in the yard, green or gray access lids, an alarm box on the house, or electrical wiring out to the tank. Then confirm it with the county health department or a licensed septic professional. If you're buying, ask for the permit and see our buyer's guide.

More detail on alternative systems

EPA describes several alternative designs used where conventional drainfields won't work.

• Drip distribution: effluent is dosed through small tubing inserted into the top 6 to 12 inches of soil, so no large mound is needed. The drawback, according to EPA, is that it needs a large dose tank after the septic tank, plus electrical power, which adds cost and maintenance.
• Aerobic treatment units (ATUs): these work like a small version of a municipal sewage plant. They inject oxygen into the treatment tank, which increases bacterial activity and treats nutrients more thoroughly. Some include a pretreatment tank and a final disinfection step.
• Mound systems: used where soil is shallow, groundwater is high or bedrock is close. The drainfield is built above the natural ground in a constructed sand mound, and effluent is usually pumped to it.
• Recirculating sand filters: effluent is pumped through a sand filter, often several times, before dispersal. This gives a high level of treatment.
• Evapotranspiration systems: used in dry climates, where effluent evaporates or is taken up by plants rather than soaking into the soil.
• Constructed wetlands: effluent passes through a lined wetland cell where plants, microbes and media treat it before final dispersal.
• Cluster or community systems: several homes share a treatment system, often managed by an association or utility.

Maintenance by system type

System	Typical service needs
Conventional gravel or chamber	Inspection at least every 3 years and pumping about every 3-5 years, per EPA
Systems with pumps, floats or aerators	Inspection generally once a year, per EPA, often under a service contract
ATU	Regular servicing of aerator and controls, plus any disinfection unit
Mound or sand filter	Pump and alarm checks, plus periodic inspection of the filter or mound
Drip	Filter cleaning, line flushing, and controller and pump checks

EPA stresses that a service contract matters for alternative systems because they have mechanical parts.

Alarms and power

Many alternative systems have a high-water alarm. If it sounds:

1. Cut water use right away.
2. Check whether a breaker tripped or the power is out.
3. Call your service provider. Don't keep silencing the alarm.

During long power outages, systems that depend on pumps can't move effluent, so use as little water as possible until power returns.

Key takeaways

• System type depends on soil, slope, lot size, water table and local rules.
• Alternative systems treat wastewater on difficult sites but need more upkeep.
• Know your system's alarms, and keep a service contract if you have mechanical parts.
• Find your type in permit records or ask your health department.