There are really only two septic system types in the sense that matters: gravity systems that let the soil do the work, and engineered systems that treat or pump the water because the soil cannot. Everything in the catalog is a variation on one of those. Which one you get is decided by a soil test and a tape measure, not by preference, so this page is organized by what each design is actually solving.
What are the 3 types of septic systems?
The question usually means the three you will meet on a residential lot: conventional gravity, aerobic treatment and mound. Conventional is the default and much the most common. Aerobic adds oxygen so the effluent leaves cleaner. A mound builds the field above grade where the ground itself is not usable. Everything below is the longer list.
| Type | Installed | Running | Used when |
|---|---|---|---|
| Conventional gravity | $6,000 to $15,000 | Pumping only | Soil percs, room available |
| Chamber | $6,500 to $16,000 | Pumping only | Tight lot, no gravel nearby |
| Pressure distribution | $9,000 to $20,000 | $100 to $300/yr | Even loading needed |
| Aerobic (ATU) | $10,000 to $25,000 | $400 to $900/yr | Slow perc, small lot |
| Sand filter | $12,000 to $28,000 | $300 to $600/yr | Poor soil, high standard |
| Mound | $15,000 to $35,000 | $200 to $500/yr | High water table, shallow rock |
| Drip dispersal | $12,000 to $25,000 | $300 to $700/yr | Slope, shallow soil |
Conventional gravity
A tank and a trench field, with water moving by gravity the whole way. Nothing runs on electricity and there is nothing to service but the tank. Where the soil percs and the lot has room, this is the right answer and no amount of technology improves on it. It is also the cheapest to own by a wide margin, which matters more over thirty years than the install price.
Chamber systems
The same gravity design with plastic arch chambers instead of pipe and gravel. Most codes grant a 20 to 40 percent smaller field, which makes the difference on a tight lot, and no gravel truck has to reach the back yard. Ownership is identical to conventional. Leach field chambers is the sizing, cost and gravel comparison.
Aerobic treatment units
A blower drives air through the wastewater so aerobic bacteria treat it far more thoroughly than anaerobic digestion does. The effluent is clean enough that many states allow a reduced field, and in parts of the Southwest, surface spray. The cost is permanent: a blower running continuously, and a maintenance contract that most states require by law.
Mound and sand filter
Both manufacture the soil the site is missing. A mound builds the absorption bed in imported sand above grade to get vertical separation over a high water table or shallow rock. A sand filter passes the effluent through a sand bed for treatment first, so a much smaller absorption area is acceptable. Both need a pump, a designer and a bigger budget.
Old system types you may inherit
- Cesspool. A lined or unlined pit that discharges untreated. No treatment, no field. Banned for new construction essentially everywhere and required to be replaced at sale in a growing number of states.
- Seepage pit or dry well. A tank feeding a deep gravel-filled pit instead of shallow trenches. Common before the 1970s, now prohibited in most codes because the discharge is too deep to be treated.
- Steel tank. Not a system type but worth knowing: steel tanks rust from the inside and lids fail suddenly, which makes them a safety issue as much as a performance one.
- Tank with no field. Older rural systems sometimes discharge to a ditch or a stream. Illegal now, and a real liability at sale.
An old system can usually stay in service while it works. It generally cannot be repaired in place to the old standard, and many states require an inspection or an upgrade at the point of sale. If you are buying a house with a cesspool or a seepage pit, price the replacement as part of the purchase.
How the type gets decided
- Soil evaluation and perc test. Sets the loading rate and whether the site works at all.
- Water table and bedrock depth. Decides conventional against mound.
- Usable area after setbacks. Wells, surface water and property lines, plus the required reserve.
- Design flow. Bedrooms, not occupants.
- The county code. Some counties simply do not permit certain designs, whatever the soil says.
Types of sewer systems for homes
Outside of a septic system the choices are municipal sewer, which costs a connection fee and a monthly bill but nothing to maintain, and the small shared systems: a community cluster system where several houses share a treatment field, or a grinder pump connection where the house is below the sewer main. If a sewer line runs past your lot, connecting is almost always cheaper over twenty years than replacing a failed septic system.