What are the typical problems with a soakaway tank

Posted by Callum Vallance-Poole, on March 28, 2022.

No matter how big or small your soakaway tank, at some point you will experience an issue that requires it to undergo maintenance or repairs. There are several factors that can lead to the failure of a soakaway tank, including things like soil quality, maintenance, and the height of the groundwater ground table. In this article we cover some of the typical problems with a soakaway tank and some of the signs you should look out for.

Soil type and/or groundwater table

Effluent cannot dissipate into a clay or clay-based soil in a typical soakaway drain field. This is because they have very poor levels of porosity and in many cases a soakaway can fail in as little as 5 years when installed in such an unsustainable soil.

When this type of soil starts to receive excess sodium (in the form of salt found in detergents etc.) it can lead to something called sodium binding. When this reaction occurs, clay particles start to bind together to form a waterproof layer along the soakaway trench.

High levels of suspended solids can also sometimes be found this type of low porosity soil, which ultimately reduces the effectiveness and life of the soakaway. If a similar level of suspended solids is present in sand soils, which will also reduce the porosity. During the winter period, the groundwater table can become higher than the septic tank outlet level, which can affect settlement chambers to integrate with the clarified effluent, reducing the soil’s porosity.

Bad maintenance

If a soakaway is attached to septic tank, then maintenance will play an important role in the upkeep of performance levels. Unfortunately, it is often the case that the system is not kept in the condition they should be to ensure remans efficient.

Septic tanks will need to be emptied at least once a year, as their capacity usually lasts for 12 months. If the sludge gets washed into the soakaway system the soil’s porosity is significantly reduced, and the effluent will be prevented from soaking away. Tank owners should ideally hire a professional company with experience in this area, as they will know the correct maintenance procedures to follow to ensure the tank is emptied correctly and it can continue to separate waste efficiently.

Incorrect soakaway depth

Despite the Building Regulations stating that drainage fields should ensure aerobic contact between the liquid effluent and the subsoil, it can often be the case that the outlet levels in modern ‘onion’ shaped fiberglass septic tanks are more than a meter below the ground. This can result in a soakaway that uses anaerobic conditions after leaving the septic tank.

The soakaway depth needs to be less than a meter below ground level due to their construction. The soil should contain oxygen, which is only found in the first top metre The ground acts as a medium to disperse the effluent, while also being part of the system to break up and digest the effluent, with the aerobic bacteria in the soil carrying out this sewage water treatment.

The soil’s porosity will be lower as there will be a different type of bacteria present that produces a slime, leading to a reduced life of the soakaway, instead of breaking down the affluent. This happens under ‘non-aerobic’ conditions and occurs because there’s not enough oxygen present.  

Increased usage

You may have bought a house that only had one or two people using the system and if you are a larger family, you could be putting more demands onto the system. This will mean the amount of water going into the soakaway will increase quite significantly and add pressure that wasn’t previously there.

The last owners of the system may not have experienced any issues, but increased usage could mean that you do. So, if you are buying a property with a septic tank treatment system it is important to be aware of its capacity and the amount of usage it will experience once you move in.

How can you tell if a soakaway has a problem?

The most common symptom of a failed soakaway is when the wastewater is unable to leave the tank. As a result, the system will eventually reach capacity and any wastewater attempting to enter the system will not be able to access the tank. If the problem is not spotted and repaired, any holding point inside the system will start to overflow, along with open drain points and inspection chambers. The end result will be overflowing drains and toilets, broken appliances and the arrival of bad smells and odours inside your property.

Due to their design, it is inevitable that a soakaway will eventually fail and need some form of repair. When this happens will depend on a range of factors, which is why maintenance plays such a important role in ensuring the longevity of the system.

In most cases, the symptoms that arrive because of a failed soakaway are similar to those of a blocked and repairable soakaway. Most systems can usually be repaired unless they have been left in poor condition for quite some time. While you will be able to see the issues caused by a broken soakaway, identifying the exact cause can be difficult, and you will usually need to hire a professional company to assess the entire system.

If you want to attempt this yourself, you will have to check the filters to see if they are blocked. Where the system is not discharging to the soakaway then the problem will likely be located elsewhere. A section of the soakaway will need to be excavated to see if the water flows easily into the excavated hole. If the water does flow freely and you see the soil remains black and pungent then it is likely a failure will occur. When the water doesn’t flow freely, then the failure, blockage or problem is probably with the soakaway system.

Marketing Coordinator - Based at our UK HQ in Banbury, Oxfordshire, Callum is responsible for promoting Water Management Systems, Attenuation Tanks, Treatment Plants, Rainwater Harvesting Systems and more!