Photograph of  a conventional septic tank during installation.Required Septic Tank Depth
Septic tank design depth - how deep do we put the septic tank below ground?

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Septic tank design depth:

To what depths are septic tanks or cesspools or seepage pits or drywells commonly buried? Here we describe the depth at which septic tanks are installed and we describe several factors that influence the acutal depth to which a septic tank (or cesspool or drywell or soak-pit) will be buried.

A companion article linked-to at the end of this one explains the septic tank depth sketch shown at the top of this page and describes in detail how to find the actual depth of an existing installed septic tank.

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Septic Tank Installation Depth

Photograph of  a conventional septic tank during installation.[Click to enlarge any image]

Article Series Contents

How Deep Should We Put the Septic Tank at Original Installation?

Septic tanks can be installed pretty much at any depth in the soil. Even in freezing climates, the septic tank serving an occupied home or even an unoccupied one is unlikely to freeze, partly because of latent heat the bottom of the septic tank receives from the earth and partly because of the heat generated by the bacterial action going on in the septic tank. (DO NOT add antifreeze to a septic system.)

Factors Determining Septic Tank Depth

The principal factors that determine the actual depth at which a septic tank is likely to be buried (and thus how deep you may have to dig to find the septic tank) at a particular site include:

Deep septic tanks should have a service riser installed. Septic risers are large-diameter "wells" that are placed over a septic tank inlet baffle access port (and possibly outlet) to permit easy access for septic tank pumping, inspection, and baffle repair. If the septic tank happens to be buried more than just a few inches below ground surface, good practice includes installing a septic riser, a large diameter pipe that gives good access to the septic tank for inspection and cleaning.

Details are at SEPTIC TANK RISERS.

Septic Tank Location Articles


Continue reading at SEPTIC TANK DEPTH to find the depth to the cover of an existing septic tank or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see SEPTIC DRAINFIELD SIZE for specifications for disposal field trenches, layout, size, setbacks, trench depth, etc.



Or see U.S. SEPTIC AUTHORITIES & DESIGN SPECIFICATIONS - sources of septic system design, installation, inspection, testing, codes & regulations

Suggested citation for this web page

SEPTIC TANK DESIGN DEPTH at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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