Septic Systems 101: Cesspools
Cesspools are underground pits or containers for wastewater. They are an outdated onsite wastewater management option used before septic tanks. A cesspool is usually quite deep and several feet in diameter. They are sometimes lined with stone, concrete rings, or a similar strong material. The area around the pit, between the soil and wall material is filled with gravel to help filtration when effluent leaves the cesspool from intentional space between the structure’s material. Many times cesspools will be topped with a concrete lid that is then backfilled with soil on top. If you have a cesspool we recommend placing a stake in the ground above the lid next time you have it pumped to remember it’s location. We also recommend an inspection port be installed so you can have it pumped regularly or in case of emergencies, as most cesspools did not have access for pumping when they were installed.
Though they are not installed anymore, we do find we received a couple of calls every month asking about maintenance for a currently used cesspool. Most cesspools can be found in much older suburban areas. Rarely an old urban building will have a cesspool in a basement. Cesspools were installed in the mid 20th century with the thought that by the time they failed many of the homes would have access to sewer. Unlike septic systems, they are not meant to last a long time with regular maintenance. Many counties and local health offices prohibit cesspools and their construction due to high failure rate and an increase in groundwater protection. Though they are now uncommon, we believe it is beneficial for current cesspool owners or those looking purchasing at a home with a cesspool to further understand how they work, their maintenance options, and the issues they may run into with this type of system.
Cesspools differ from septic systems in that they are just comprised of one main working part- an underground hole or container in which wastewater enters through pipes from the home. While septic systems have a drainfield to treat the effluent from a tank, as explained in The Septic Drainfield, cesspools acts as a tank and drainfield. Cesspools use the soil around the walls of a pit or have several holes in the container that effluent can exit into the soil. The most common issue with cesspools is a back up into the home from a clogged line. Because of this they should be pumped out more frequently than a septic tanks if you regularly put solids down your drain. However, you will may have to install an inspection port to make pumping possible.
Cesspools are different from a holding tank, which is also a vertical underground container for wastewater. Holding tanks do not act as a drainfield, allowing effluent to leave and be treated by the soil surrounding it. Holding tanks must be pumped very regularly. In fact, many have an alarm that will sound when the tank is full to a certain level, alerting the owner it is time to pump.
Across America, cesspool collapses are very common. Unfortunately, many of the collapses result in fatalities as they collapse with the weight of someone above them. While we would hope every installation would be done correctly, many times these cesspools were homemade or built to save costs resulting in dangerous structural now. If you have a cesspool please make sure you take precautions to keep you and loved ones from walking over the cesspool.
Most cesspools are decommissioned when a homeowner hooks up to sewer or installs a new septic system. The rules for decommissioning vary per county. What they are filled with when they are decommissioned can vary, while some counties require they be completely removed from the ground. Most commonly in Oregon cesspools are filled with gravel mixture, though we have heard of dirt being used as well.