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How Deep Are Septic Tanks?

How Deep Are Septic Tanks?

Most homeowners are aware that septic tanks are buried underground, but just how deep are they? 

While the actual depth varies depending on several factors, a typical septic tank can be planted anywhere from 4 inches to 4 feet under the ground, and they measure between 8 feet by 5 feet.

But how do you locate your septic tank if you don’t know its depth?

Why is knowing the exact location necessary? What happens if a septic tank is buried too deep underground? 

Here we answer these questions and more. 

The Optimal Depth Of A Septic Tank

How deep a septic tank should be installed depends on many external factors that the installer must consider.

Generally, septic pipes are kept around 1.5 to 2 feet deep, and the tank is relatively closer to the surface. 

In freezing climates, septic tanks are buried much deeper underground and with extra soil on top. In some circumstances, the tank can even be as little as 3 to 4 inches under the surface with the lid exposed. 

The depth also depends on how much dirt weight the septic tank can bear, with some models having very precise requirements. 

Generally, there is no need to bury septic tanks that deeply.

They are typically kept closer to the surface, as the movement of effluent from the septic tank to the drain field is dependent on gravity. 

What Factors Determine The Depth? 

Environmental conditions, soil type, and geology all influence how deeply a septic tank is buried.

Typically, installers consider three main factors. These are:

  • The type of soil. If the earth has high clay content, there will generally be a higher water table, and the tank will be installed closer to the surface. Expert installers can determine what depth will be optimal according to the soil conditions of the land. 
  • The type of tank. While septic tank models are more or less similar, some manufacturers can build models with particular requirements. Some septic tanks can only bear the weight of 4 to 5 inches of soil, while others can have several feet of soil on top. If a tank is buried deeper than the soil level recommended by the manufacturer, it can quickly get damaged. 
  • Water table. The septic tank will be kept closer to the surface of the land and has a high water table. Burying it deep underground can affect its functionality. 
Septic Tanks

What Happens If A Tank Is Buried Too Deep? 

Contrary to popular belief, septic tanks do not need to be buried excessively deep underground. 

If the tank is installed too deep, it might not be able to function correctly with the excessive soil weight on top.

It can also cause the tank to malfunction frequently; for example, the effluent might bulk up and not naturally flow into the drain field. 

How To Locate Your Septic Tank 

It is good to be aware of the exact location of your septic tank and how deeply it is buried. 

This also becomes extremely important when the tank needs to be accessed for pumping, repair, or maintenance.

If you don’t know where your tank is buried, follow the steps below to locate it. 

  1. Locate your drainage pipes. Following your sewer pipes should lead you to the tank, as the tank and the drain field will be installed parallel to the sewage line. Look for a four-inch sewer pipe leaving your home from the basement or crawl space, and follow it. 
  2. Keep following the pipe, and probe gently with a stick or rod to ensure you are heading in the right direction. Your septic tank may be anywhere from 5 to 20 feet outside your door. 
  3. Use a stick or metal rod about 5 feet deep to locate the septic tank lid. Push the rod gently into the soil till the tip touches the cover. Be careful not to apply too much pressure, as this can harm the surface of your tank. 

What To Do If You Can’t Locate The Tank 

If probing around with a steel rod doesn’t work, you can check your land’s property papers.

These papers generally have details on the land’s construction and landscape.

Summing Up How Deep Septic Tanks Are

While the actual depth of each specific septic tank will vary depending on a multitude of factors, they are generally buried anywhere from 4 inches to 4 feet below the ground.

If you cannot find where your septic tank is located or how deep it is, check the original property papers.

Lindsay Reed

Hi, I'm the founder of! I created this website to be a resource for everyone who wants to make the best home possible.