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A soakaway is a pit or crate-based structure used for the attenuation and gradual release of rainwater (surface water) into the ground. Soakaways were historically used to receive septic tank effluent, but this has not been legal since 2007 and should not be confused with a drainage field.

A drainage field (also called an infiltration system) is the legal method of discharging treated effluent from a septic tank or sewage treatment plant to the ground. It consists of parallel, gravel-filled trenches fitted with perforated pipes, through which the effluent slowly percolates into the surrounding soil. Drainage fields must be designed and installed in accordance with British Standard BS 6297 and the relevant Building Regulations.

No. Rainwater and surface water should never enter a septic tank or sewage treatment plant. These systems are designed to treat sewage only, and are sized accordingly. Rainwater entering the system will overwhelm the treatment process, carry settled solids and bacteria into the drainage field or watercourse, and block or destroy the drainage field over time. Building Regulations (Part H) require rainwater and surface water drainage to be kept completely separate from foul drainage. If you suspect rainwater is entering your system, contact us – identifying and eliminating this is one of the most common and important maintenance interventions we carry out.

Yes. WCI has over 40 years of experience delivering foul drainage solutions for a wide range of commercial and large domestic applications, including systems serving multiple dwellings, campsites, hotels, visitor centres, care homes and industrial complexes. For commercial projects, we provide a full service: design, value engineering, installation, Environment Agency permitting, Building Control sign-off and ongoing maintenance. Call us to discuss your project.

Yes. For clients who already have a groundwork team on site, or who have the skills and resources to complete the installation themselves, WCI can design the system, supply the required tankage and components, and commission the system once it has been installed. We can also be available to provide technical guidance during installation if required.

Typically, the existing septic tank is emptied, decommissioned, infilled with suitable compressible material and the surrounding area is levelled and reinstated. If the new sewage treatment plant must be installed in exactly the same location as the existing tank, the old system will be fully excavated and the spoil disposed of responsibly.

Yes. All tankage and components installed by WCI come with the relevant manufacturer’s product warranty. WCI also provides a Workmanship Warranty covering our installation services, which is available to view on request.

You will need to submit a Building Control Notice before installation begins – this applies in all cases. Planning permission is more site-specific. All installation work within National Parks requires planning approval. Outside National Parks, small domestic installations usually fall under permitted development rights, but if you are in any doubt, we recommend consulting your local council’s planning department before proceeding. WCI can advise you on the consenting requirements for your specific site.

A standard domestic installation usually takes five working days. Where access is restricted or the installation is more complex, the programme may be longer. When we provide a quote, we will give you a clear estimate of the time required.

A straightforward domestic sewage treatment plant installation typically costs between £12,000 and £15,000, depending on the complexity of the site. Factors that affect cost include access, ground conditions, the need for groundwater management, the distance of the drainage field or watercourse from the tank, and whether the existing system needs to be excavated and removed. Contact us for a site-specific quote.

WCI is fully independent of all manufacturers, which means we select the right system for each site based on factors including cost, treatment performance, maintenance requirements, aesthetics, noise, access constraints, seasonal flow variations and the required quality of treated effluent. All systems are installed under a Building Regulation notice and will either comply with the General Binding Rules or have an appropriate Environment Agency permit applied for prior to installation.

We regularly install systems by GRAF, Marsh, WSc (formerly WPL), Premiertech Aqua, Klargester and others, and have experience with systems of all sizes and configurations.