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Septic Tank Installation

It is important to size and design your septic tank system correctly so it is compliant with all regulations. WCI provides expert septic tank design and installation services in Somerset, Devon, Dorset and Wiltshire.

WCI has been designing and installing septic tanks and drainage fields for over 35 years. Septic tanks can offer a low cost, completely silent system with simple maintenance requirements. When WCI receives a call for a septic tank installation, it is usually due to two main reasons:


1. Replacing a failed existing Septic Tank

There are a number of different reasons why an existing septic tank may require replacement. Often such problems are picked up during one of our Home Buyers Drainage Survey, when a tank is being emptied or by the home owner as problems start to occur – such as a gurgling, slow draining toilet, backed up drains, strong smells and/ or boggy wet patches where the drainage field is installed.

Common reasons to replace your septic tank are:


    • You have an illegal system. You are purchasing a property and your surveyor has requested a foul drainage inspection by an expert wastewater engineering company. WCI arrives on site and finds that the existing septic tank discharges directly into the local watercourse. The system is condemned as illegal as it does not meet the Environment Agency’s General Binding Rules and WCI quotes to upgrade the system with a replacement sewage treatment plant or, where it is suitable, with the installation of a BS compliant drainage field.
    • Often older fibreglass tanks can suffer with the internal baffle or ‘skirt’ collapsing into the tank. The hooks that hold the baffle up (placed in the neck) can corrode or dislodge when the tank is incorrectly emptied – bottom up – leaving heavy solids coating the baffle. This additional weight can cause the hooks to break or dislodge.
    • Collapse or implosion of the tank, often due to incorrect installation.
    • Tanks that have been installed without being surrounded in concrete can ‘pop’ out of the ground. In such circumstances a new tank is often installed to mitigate against any unknown, invisible damage to the tank. Some tanks function happily for years without a concrete surround but a change in location of a local spring, leaking pipes or an infrequent emptying schedule might cause the tank to become buoyant causing it to rise out of the ground.
    • You are building an extension and the existing septic tank is in the wrong place.
    • The existing septic tank is too small for modern day living. With the advent of washing machines, dishwashers and our obsession for cleanliness, we use more water today than 40 years ago. Existing septic tanks are often found to be too small, the solids don’t adequately settle out and can compromise the drainage field.
    • Structural damage caused by tree roots.
    • Vehicle damage when a car, tanker or ride on mower drives over the tank. It happens more often than you think!
    • Thinking greener. Although septic tanks are a legal way of treating foul water from domestic properties, they are a very simplistic and sewage treatment plants treat foul water to a much higher standard. Some people are looking to upgrade their septic tank with a more ‘environmentally friendly’ method of waste water treatment.
    • Please note that minor damage to dip pipes, vents and covers can often be repaired and does not always mean your existing tank needs to be replaced.

2. Installing a new Septic Tank and Drainage Field

The installation of a septic tank and a drainage field is still permissible in England as long as the system meets the Environment Agency General Binding Rules and is designed and constructed in line with Building Control Regulations and British Standards.

Sizing a new septic tank is a very simple calculation which is based on the maximum number of bedrooms in a property. Care should be taken when a property has a self-contained annex, as this building will be treated as a separate dwelling under British Water Flows and Loads 4.

What is more important is that consideration is given to the required secondary treatment – commonly a drainage field. It is important that porosity tests are undertaken along with an adequate trial pit where necessary. This will establish the ‘drain-ability’ of the soil, the resting ground water table and provide WCI with the data to design and size the drainage field in accordance with BS 6297:2007+ A1:2008. This is required to gain a Building Control completion certificate for the installation.

WCI provides expert septic tank design and installation services. The process starts when you call or email our offices with an enquiry. After a detailed chat, we undertake a desk top study which is used by our engineers to educate them about your site prior to the site visit. A WCI engineer will carry out a detailed site survey to ensure a comprehensive quotation can be sent to the client following on from the site visit. WCI is equipped to undertake porosity testing. Please speak to the office for more information.

If you require a Septic Tank to be installed, please contact WCI on 01984 623404 or via our contact form below to arrange your free site visit.

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If you have any questions or just need some clarification on the regulations and how they apply to your property, please call us on 01984 623404