Photograph of  a seepage pit collection at the factory Using a Cesspool for onsite septic wastewater disposal.
Cesspool construction, maintenance, troubleshooting, repairs. How do cesspools fail?

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Cesspool type septic systems:

This article explains what a cesspool is, gives important safety and maintenance advice for cesspool systems, and defines the criteria for cesspool failure.

We also provide critical safety warnings concerning cesspool systems as with some older and especially site-built cesspools there is a risk of dangerous collapse or cave-ins.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Guide to Using a Cesspool for Onsite Sewage Disposal - properties of cesspools used for onsite wastewater disposal

What is a cesspool? A cesspool combines the septic treatment tank and absorption system into a single component. A cesspool is not a septic tank and does not work like one.

In its most basic and traditional form a cesspool is a hole in the ground to receive sewage: the walls of the "hole" are lined with stone or concrete block or (safer) pre-cast concrete (photo) to form a masonry-lined pit into which sewage is discharged. Solids (sewage from the building) remain in the pit, effluent is absorbed into soil below and at the sides of the cesspool.

Solids settle to the bottom, floating grease and scum collect at the top, and liquid seeps into the ground, initially through the bottom and most of the time through the side of the cesspool.

Cesspools as a means to dispose of sewage have been around since the late 1400's at the beginning of the Renaissance. (Before that people simply tossed their night soil into the street.) While cesspools have been used for a long time, since the development of the more modern septic system (tank and drain field) cesspools have often used where there is limited physical space (no room for a leach field), and perhaps where the soil absorption rate was high such as areas of gravel or sandy soils.

For most buildings and onsite waste disposal installations which use a "cesspool", you should consider the use of a cesspool as an obsolete, limited capacity system likely to need replacement, and involving significant cost. Some immediate concerns are stated next.

Cesspool Failure Criteria (MA)

Failure Criteria for Cesspools is given by this basic but widely-used definition of a failed cesspool that needs replacement:

If the waste level is within 12" of the inlet pipe near the top of a cesspool the system is at end of life and needs to be replaced.

Some municipalities and experts will state other distances.

In the U.S. in Massachusetts according to the Massachusetts Title 5 Septic Law the following are considered a failed or unacceptable cesspool installation:

A cesspool needs replacement if it meets any of these failure criteria. While a septic company may offer to pump, partially pump out, or agitate or aerate the bottom sludge in the cesspool in an effort to extend its life, these procedures are potentially very dangerous and at best will give only temporary relief.


Photograph of  a seepage pit collection at the factory Where a new cesspool of traditional sort is going to be installed you should at least use a concrete pre-cast model with a safe cover (see photos at left and above).

Fortunately there are alternative onsite wastewater disposal alternative designs which can handle limited or even zero-space sites, so a simple cesspool as a destination for blackwater is no longer the only choice for limited-space sites.

Are Cesspools Even Legal?

Watch out: cesspools are not legal for use as wastewater treatment and disposal systems. In some areas existing cesspools used for wastewater handling [no conventional cesspool adequately treats wastewater] may be "grandfathered" in and permitted to continue in use.

But home buyers purchasing a property served by a cesspool should keep in mind not only the limited function of such systems but the significant cost that will be faced when the system is no longer functional - because at that time the local authorities may require that a different, more effective wastewater treatment system be installed, such as a septic tank and drainfield. And space limitations on a property can cause real trouble when the cesspool has to be abandoned.

Cesspools are flatly declared "not legal for use as wastewater treatment and disposal systems" in other jurisdictions such as in the Alaska state sanitary code. [4]

Cesspool Safety Warnings and Cesspool Capacity Limitations

Very Important Cesspool Safety Warnings

In summary about cesspool hazards: watch out for cave-ins, keep away: cesspools, particularly older site-built cesspools present a very high risk of collapse from an unsafe cover or following some types of service involving pumping, aeration, or hydro-jetting.

Adults or children should not walk over or even near cesspools because of the risk of falling-in followed by collapse, a virtually certain cause of death. If the presence of a cesspool is known or suspected at a property its location should be roped off to prevent access and it should be investigated by a professional.

Cesspool Capacity and Testing Limitations

Cesspools can obscure or prevent effective septic loading and dye testing: If a cesspool is in use at a property a septic dye test would not be a reliable indication of good system condition since the test could simply be trying to fill a large near-empty hole in the ground; yet such a system may fail soon after being returned to active or heavier regular use.

Cesspool Treatment Chemicals

Reader Question: my friend said dump a 50 pound bag of lime into the cesspool

Does lime help to break down the walls in a cespool. My friend said to dump a 50 pound bag in. He said his friend did it and it ate the walls and his pit is working great. He also said he saw cracking in the side walls and after adding the lime the sides of the walls basically fell in. This was concerning to me. - Lance 5/11/12 (originally asked at SEPTIC TREATMENTS & CHEMICALS)

Reply: do not add lime to a cesspool; watch out for fatal cesspool collapse hazards


A cesspool is intended to treat the sewage it receives, discharging effluent into soils around the cesspool itself.

While there is a sound argument that no cesspool adequately treats raw sewage and thus none is really sanitary, dumping lime into the cesspool is going to kill off cesspool bacteria, hastening its ruination and reducing still further its treatment of sewage. It would be a mistake. Your friend is mistaken and is likely to cost you plenty.

Watch out: cracking in the cesspool sides, if you mean the structure of the cesspool, is would be extremely dangerous, risking a cesspool collapse. There have been fatalities from just that cause when someone fell into and was buried alive in a collapsing cesspool.

If you do not know the condition and safety of your cesspool cover and structure, or if there is any indication of cracking or shifting of the cesspool, you should immediately block off all access to the area while you wait for an experienced contractor to excavate, diagnose, and repair or replace the system.


This material is a chapter of our Septic Systems Online Book that explains septic system inspection procedures, defects in onsite waste disposal systems, septic tank problems, septic drainfield problems, checklists of system components and things to ask. Septic system maintenance and pumping schedules.

Home buyers who want less technical advice should see the HOME BUYER's GUIDE to SEPTIC SYSTEMS to Septic Systems.


Continue reading at CESSPOOL FAILURE CRITERIA or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


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