Above Ground Septic Tanks
When a conventional buried tank is not an option, above ground septic systems provide an alternative. Learn when you need one, what types exist, and what they cost.
What Is an Above Ground Septic Tank?
An above ground septic tank is a wastewater holding or treatment system that sits at or near the ground surface rather than being buried several feet underground. These systems are used when site conditions make conventional underground installation impossible.
The term covers several system types, from simple holding tanks that store waste until a truck pumps them out, to engineered mound systems that treat and disperse effluent through an elevated sand and gravel bed. The right type depends on your property's specific conditions and whether you need a permanent or temporary solution.
Above ground systems are more common than many homeowners realize. In areas of the Midwest, Northeast, and coastal regions where high water tables and shallow bedrock are prevalent, mound systems are often the standard rather than the exception.
When Do You Need an Above Ground System?
Your county health department or a licensed site evaluator will determine if you need an above ground system based on a percolation test and soil analysis. Common reasons include:
High water table
When the seasonal high water table is within 2 to 4 feet of the surface, a buried tank and drain field would sit in saturated soil, preventing proper treatment and risking contamination.
Shallow bedrock or hardpan
Rocky soil or bedrock close to the surface makes it impossible to excavate deep enough for a conventional tank. An above ground solution avoids the need for deep digging.
Poor soil drainage (heavy clay)
Clay soils that drain too slowly for a conventional drain field may require a mound system with imported sand and gravel that provides adequate filtration.
Small lot size
When setback requirements leave insufficient room for a conventional drain field, a compact above ground system may be the only option that fits.
Temporary or seasonal use
Construction sites, seasonal cabins, and temporary events may use above ground holding tanks that are pumped regularly rather than treating waste on-site.
Types of Above Ground Septic Systems
There are two primary types of above ground septic solutions, each suited for different situations:
Holding Tanks
A holding tank is a sealed container that collects and stores all wastewater until a pumping truck removes it. There is no on-site treatment or discharge — everything is hauled away to a treatment facility.
- -Best for: Seasonal properties, temporary sites, very small lots
- -Cost: $1,500-$3,000 for the tank
- -Ongoing cost: $200-$400 per pump out (may need monthly pumping)
- -Capacity: 500-2,000 gallons
Mound Systems
A mound system is a permanent septic solution where an elevated mound of sand, gravel, and topsoil is constructed above the natural ground level. Effluent from a septic tank is pumped into distribution pipes within the mound, where it filters through the engineered layers before reaching the natural soil below.
- -Best for: Permanent homes with high water table or poor soil
- -Cost: $10,000-$20,000+ installed (tank + mound)
- -Requires: Dosing pump, timer, and engineered design
- -Lifespan: 20-30 years with proper maintenance
Above Ground Septic Tank Cost
Above ground septic systems generally cost more than conventional buried systems due to the specialized engineering and materials required:
| System Type | Tank / Equipment | Total Installed |
|---|---|---|
| Holding tank (500-1,000 gal) | $1,500–$3,000 | $2,000–$4,000 |
| Holding tank (1,500-2,000 gal) | $2,500–$5,000 | $3,500–$6,000 |
| Mound system (residential) | $3,000–$6,000 | $10,000–$20,000 |
| Mound system (large/commercial) | $5,000–$10,000 | $15,000–$30,000+ |
Prices vary significantly by region and site conditions. See the full installation cost guide.
Pros and Cons
Advantages
Disadvantages
Regulations and Permits
Above ground septic systems are subject to stricter permitting requirements than conventional systems in most jurisdictions. Here is what to expect:
Site evaluation and soil testing
A licensed evaluator must perform percolation tests and determine the seasonal high water table before any system design can begin.
Engineered system design
Mound systems typically require engineered plans drawn by a licensed designer or PE, which can cost $500-$2,000.
Health department permit
Your county health department must approve the system design and issue an installation permit before work begins.
Installation inspection
An inspector must verify the system is built according to the approved plans at multiple stages during construction.
Operating permit (some states)
Some states require an annual operating permit for above ground systems, which may include mandatory inspections.
Important: Never install an above ground septic system without proper permits. Unpermitted systems can result in fines, forced removal, and make your property unsellable. Contact your local health department first.
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Frequently Asked Questions
What is an above ground septic tank?
An above ground septic tank is a wastewater holding system that sits on or near the surface of the ground instead of being buried underground. They are used when site conditions — such as a high water table, shallow bedrock, or rocky soil — make it impossible or impractical to install a conventional underground septic tank.
How much does an above ground septic system cost?
An above ground septic system costs $1,500 to $5,000 for the tank and basic setup, but a complete mound system (which is the most common above ground solution) costs $10,000 to $20,000 or more installed. The higher cost compared to conventional systems is due to the engineered fill, sand, and gravel layers required.
When do you need an above ground septic tank?
Above ground systems are needed when the water table is too high for a buried tank (less than 2-4 feet from the surface), bedrock is too close to the surface, the soil has poor drainage (heavy clay), the lot is too small for a conventional drain field, or the system is temporary (construction sites, seasonal properties).
Do above ground septic tanks freeze?
Yes, above ground septic tanks are more vulnerable to freezing than buried tanks because they lack the insulating benefit of being underground. In cold climates, above ground tanks and mound systems require insulation, heat tape, or regular use to prevent freezing. Seasonal properties in northern states may need to winterize the system.
Are above ground septic tanks legal?
Above ground septic tanks and mound systems are legal in most states, but they require specific permits and must meet local health department regulations. Many jurisdictions have strict design requirements for above ground systems, including engineered plans, soil testing, and inspections. Always check with your county health department before installing one.