Identifying Your System

Download Print-Friendly Fact Sheet: Typical Home Wastewater Treatment Systems


Older, outdated system

Older System

Image credit: New York State Center for Clean Water Technology

If your home is older than 1973 and your house has not been expanded, it is likely to be a cesspool. If, when a septic professional opens the manhole to your system, the first pit on the pipe exiting your home is made of brick, concrete block, or has openings in the sidewall, it is a cesspool.


A cesspool is basically a pit with open joints. The old ones were made of brick or block. Newer ones are usually concrete rings with openings in the walls. Block, brick, or stone cesspools are hazardous are prone to sudden collapse, opening a huge pit in your yard.

Often there are two cesspools in line. This often means that the first has clogged and ceased to function. There is still no treatment of the wastewater.


Image credit: Peconic Green Growth

Treatment Process:


A cesspool does not treat wastewater. It just disperses it to the soil. With its open joints, a cesspool is more susceptible to flooding when the groundwater table is near the surface.


Cesspools provide little treatment or nitrogen mitigation. Cesspools just disperse wastewater to the soils. These antiquated systems do not meet current codes. Due to their grandfathered status, typically when they fail, people simply install a second cesspool downstream of the first failed cesspool. Functionally, this is no more effective treatment than the original installation.

Issues with cesspools:

Brick and block cesspools are dangerous. The old brick cesspools can collapse; typically when extra weight is above them (even just a person and a lawnmower.) People have been killed this way.

Dissolved solids are transported to the soil where particles clog the air spaces in the ground. The flow of wastewater can be blocked, leading to surface ponding or backup into the house.

If a cesspool is positioned too close to groundwater, there is a danger that pathogens (such as bacteria and viruses that cause disease) in the dissolved solids may enter groundwater and surface waters. This can lead to illness. The presence of pathogens is the leading cause for beach and shellfish bed closures.

The frequency for maintenance is difficult to calculate for cesspools, as once a cesspool starts to fail (soils clog), the time needed between pumpouts shortens. Failure for a cesspool often means dealing with the surrounding soils as well as the system itself.

When located in very sandy soils, the owner is often happy – never needing a pump-out! The cesspool is DRY!!! But guess where all that wastewater went? Directly to groundwater and then to our harbors and bays. While the owner is happy with a low-cost, functional disposal system, environmental impacts are not addressed.

 Septic System

Current code

In 1973 new codes required installation of septic systems.

Septic System (current code)          

Current System

Image credit: New York State Center for Clean Water Technology


On Long Island, a popular version of a home wastewater system incorporates a septic tank, followed by one or more leaching pool or leaching pit. The leaching pit resembles a cast concrete ring cesspool.

Treatment Process:

The septic tank provides primary treatment, allowing the solids to drop out of the wastewater and settle at the bottom of the tank. The fats, oils, and greases (FOG) float to the top. It is the thicknesses of these layers that trigger a need for a pumpout. Microorganisms that work in an environment without air process roughly 40 to 90% of the solids in the septic tank. The longer wastewater stays in the tank before exiting the system, the cleaner the wastewater will be (system designers seek at least a 24-hour residence time.)

Preferred Two-chambered Septic Tank

Image credit: Peconic Green Growth

Image credit: Peconic Green Growth


Cleaner water from the middle layer (now called “effluent”) then (typically, on Long Island) enters a leaching pit – usually stacked, perforated concrete rings. Microorganisms in the soil around the leaching pit continue the treatment process as the effluent disperses to the groundwater.

Systems with a functioning septic tank do treat the wastewater to prevent most harmful bacteria from reaching the groundwater if properly designed and installed.

Regular pumping of the septic tank ensures that the wastewater remains there long enough for the solids to settle out. A tank that has not been properly maintained and becomes filled with solids sends all of the waste – including solids – to the leaching pit, just like a cesspool. Once the outlet to the leaching pit clogs, the sewage will either pool on the surface or back up into your house.

Leaching pits must be located a minimum distance above the groundwater on your lot and horizontally distant from drinking water wells, streams, ponds, and shorelines. This may require several shallow rings instead of one deep one in locations with a high water table.

Leaching Pit

Leaching Pit

Image credit: Peconic Green Growth


While a septic system treats the solids, allowing a cleaner effluent (wastewater leaving the system), and removes significant percentages of pathogens, the removal rate of nitrogen is only 5- 15%. Nitrogen in high concentrations has recently been recognized as a serious contaminant in drinking water and in harbors and bays. In sensitive areas, the removal goal is higher, seeking a 50-90% reduction in nitrogen compounds. Leaching pits function reasonably well, stand up to abuse, and take up relatively little space. The wastewater enters the soil at a greater depth, where there are fewer microorganisms and air for continued treatment in the soils. Also, due to their small footprint, pressure speeds the flow, thus lessening the chances for natural processes in the soils to function in removal of contaminants.

The bottoms of the leaching pits need to be several feet above groundwater. Where there are shallow depths to groundwater, a system may have multiple, shallower leaching pits in order to maintain these clearances. These systems will fail – from an environmental point of view – when this clearance is not maintained or if soils drain too quickly. As groundwater levels rise due to climate change, more systems will fail environmentally, as the clearances from the bottom of the systems to groundwater will shorten.

BETTER: Septic Tank and Leaching Fields


In this configuration, wastewater leaving the septic tank is dispersed widely, closer to the surface through a series of perforated pipes rather than through leaching pits. While this solution requires more space and may be more expensive to install, it reduces pressure and will support natural and complex treatment in the soils (more air and microorganisms). There are new dispersal techniques that place the effluent into the top 18 inches of soil. The latter options can remove roughly 25-50% of the nitrogen compounds.


In septic systems, only the primary treatment phase is controlled. Natural conditions are relied upon to provide the secondary and/or tertiary treatment needed to fully process wastewater.

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This website was prepared for the C.E.S.S.P.O.O.L. Project with funds from the New York State Department of State through Title 11 of the Environmental Protection Fund