How Long Do Septic Tanks Last?

Septic tanks are a type of onsite sewage facility. They are frequently used in rural areas not connected to a sewerage system. After 23 years in the septic tank servicing industry, I've found that most folks do not understand how their septic system works or how to properly care for one.

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Septic Tank Types and Design

Most septic tanks are made from either concrete, plastic, or fiberglass. In the past, some tanks were produced from steel. However, metal tanks have now been banned in many states. Steel tanks are prone to rusting, which leads to perforations and potential collapses. It can also make them difficult to remove. 

What is The Average Lifespan of a Septic Tank?

Plastic and fiberglass tanks will last virtually forever as long as they are installed by a professional plumber with great care. Most of the failures we see are due to incorrect installation depth or how the area around the tank was backfilled. If they are buried too deep, the weight of the soil on top can cause the tank to become distorted and possibly crack. Each manufacturer has guidelines for tank installation depth. The ground is always moving, so backfilling around a tank with sand, gravel, or clean dirt will protect the tank long term. Conversely, using rocky soil to backfill around the tank can permit rocks to rub a hole in or puncture the tank over time.

The life span of concrete tanks will depend on the manufacturer, and the year they were built. Different states have varied rules on tank production.

Tanks built before the 1980s usually have a concrete or cast iron pipe baffle assembly. The cast iron usually closes up as it degrades, like a clogged artery, thus slowing or stopping flow through it.

The concrete baffles of this era usually decay; either the top erodes or the whole baffle falls off into the tank, allowing solids to float across the top and right on out to the lateral field. In the 1980s and 1990s, to correct the problems with the concrete and cast iron baffles, tanks often had a plastic baffle fastened to the walls of the tank. They work well until the steel fasteners attached to the walls decay and break off, allowing the baffle to come loose and fall into the tank. Concrete tanks built from the mid to late 1990s are made with PVC pipe baffles. They will last forever, as will plastic and fiberglass tanks.

What Are Factors That Affect The Lifespan of Septic Tanks?

Humans are the greatest threat to a tank's life span, as with most things. When installed properly and maintained appropriately, a tank will generally last multiple lifetimes if protected from human mistakes or natural catastrophes. Examples of natural disasters include a tree falling on the tank or a severe lightning strike (which I've only seen once).

In regions where earthquakes occur, tanks can crack or break. A heavy tree falling over a tank lid can crack or break the lid. Human mistakes, such as people who decide to drive or park heavy objects like equipment or vehicles above the top of the tank, can cause the top to be cracked or caved in despite being buried. I've also seen people build room additions or decks over part or all of the tank. At best, this makes it hard to maintain the septic tank. At worst, the weight on the tank will be too heavy and cave in the top.

It's also important to know what kinds of trees are planted where your septic system is located. Certain types of trees are more aggressive when seeking water supplies, and their roots can break pipes and grow through seams or cracks and, over time, can stop the flow or even fill up the entire tank with seeds. Check out our BBBseptic.com blog for more on this topic.

What Are Signs of an Aging Septic Tank?

The outside of tanks will often show cracks, breaks, or punctures from rocks or buried sharp objects, although you won't typically see these unless you dig and uncover the tank. Signs of aging will often be detected by looking inside the tank. Water level is the key indicator.

If the level is too high, it can indicate a problem with the outgoing part of the tank, the distribution box, or the lateral line system. If the liquid level in the tank is too low, it will usually be due to a crack or puncture in the tank's sides or bottom. 

On older tanks, where the baffles are not PVC, you might see that the plastic baffles are starting to fall or have completely come off. The concrete styles may also have eroded or fallen off. A professional installation of a new PVC baffle assembly can address both types of deterioration. You might see some erosion in concrete tanks inside the water line or around where the pipes come in and out of the tank. This is usually superficial and should not be cause for concern. Having a professional service your system periodically will allow you to catch most plumbing problems before they become fatal.

What is Proper Septic Tank Maintenance?

Throughout the USA, states have different rules and regulations on how septic systems are to be installed and maintained. This is influenced greatly by the soil types in other regions, from the sandy soil along the gulf to the black dirt in the north and the wet conditions of the lowlands or dry conditions of the southwest. Some simple guidelines fit most needs, such as pumping your tank out periodically and remembering not to put any more solid materials or trash down your drains than necessary.

In Arkansas, the state requires systems to be designed with a 3-5-year pump-out schedule in mind. This means that normal usage will create a solid build, which must be pumped out to ensure they don't end up in the absorption area and damage the soil's ability to treat the water as it re-enters the natural water tables.

Read our guide to how much pumping a septic tank costs.

You also need to remember that your system is an ecosystem that needs to be balanced. Someone using a septic where the water supply is a spring or well should make it easier for the natural bacteria to grow. Where public water is used, the chlorine in the public water system will also kill or stunt the bacteria in your septic system.

It’s also important to note that the use of antibacterial soaps, bleach, detergents, and cleaners will stunt or prohibit the growth of bacteria, as will some pharmaceuticals and medical treatments like chemotherapy. Some septic system bacteria treatments can overcome these conditions.

BBB Septic and Portable Toilets

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Learn More About Septic Tanks

So, How Long Do Septic Tanks Last?

Overall, septic systems are one of the best ways of treating wastewater. When properly maintained, they will last indefinitely, and using the earth's natural processes, they are effective without using any other natural resources. Even including the cost of good maintenance, septic systems are much less expensive to operate than a monthly sewer bill.