PRIVATE DRAINAGE SYSTEMS ARE BIG RESPONSIBILITY FOR UK BUILDERS
by Derek Peverill, Commercial Manager for leading sewage solutions provider Klargester

The 2002 Building Regulations put the onus on builders to take the greatest care when specifying and installing private drainage systems.

They state that both the builder and the owner of the product could be liable for any pollution problems, and give local authorities increased powers to enforce best practice.

These regulations have far-reaching implications for builders. Not least, they mean that builders must be aware of the various sewage solutions on the market and understand when and where they could be safely used.

The law states that, if possible, an off-mains drainage property must be connected to the main sewer by gravity or otherwise via a pumping system. If this cannot be done, the other options are septic tanks, sewage treatment plants and cesspools.

Septic tanks, which allow the settlement, storage and partial decomposition of solids, were once the universal solution for properties that could not be connected to the main sewer.

However, since septic tanks do not treat effluent and need a drainage field through which that effluent can be discharged, they are not suitable for sites that are likely to become waterlogged or have poorly draining soil.

Other local factors can also render septic tanks impractical and these are clearly stated in the H2 building regulations. For example, a septic tank cannot be installed within 10m of a watercourse, within 1.0m of the local water table, within 50m of a borehole, or within 7m of any domestic habited building.

If a property is in a poorly drained area, then a sewage treatment plant, such as the Klargester BioDisc, is often the best answer. Sewage treatment plants provide an environment in which bacteria are cultivated to break down sewage. The bacteria survive by using biological matter in the sewage as a food source.

Treatment plants can remove up to 95% of the biological pollutants present in sewage. Since the effluent is of a very high quality, it may be discharged directly into a river, stream or ditch, with Environment Agency permission. This means that poorly drained soils and areas with a high water table are not a problem, provided there is a suitable watercourse nearby.

To help purchasers choose the right product, a new European standard has been developed to define the minimum product requirements for small wastewater treatment systems. The standard details a long-term performance test, which will see the key performance indicators of each product clearly stated on the CE (Communauté Européenne) marking label, and allows approved manufacturers to trade across the European Union. Klargester's BioDisc has already been tested and certified to these exacting standards.

Size is particularly important when specifying a sewage treatment plant, since no plant will function effectively if it is too small. This issue has been simplified by the recent re-launch of British Water's Code of Practice, which aims to promote the collection of accurate and complete information by providing a clear data collection method. One of its key features is a detailed table of loadings for sewage treatment plants.

If a property is in a particularly sensitive area and the local authority demands a higher quality of effluent, a reed bed may be used to complement a sewage treatment plant. Reed beds from Klargester are packaged products, which are installed in the ground and filled with reeds and gravel.

If ground conditions are unsuitable for a septic tank and there is no watercourse into which effluent from a sewage treatment plant can be discharged, then a cesspool may be the only answer. Cesspools are watertight tanks, which are installed underground. They simply store sewage and do not treat it in any way; this means they have to be emptied regularly.

As a guide, a cesspool should have a storage capacity of 18,000 litres for two people and this should be increased by 6,800 litres for each additional user. There should be no openings on the tank other than for emptying and ventilation. As with septic tanks, the cesspool should be within 30m of the access point for cleaning and emptying.

To ensure best practice, builders should liaise with the Environment Agency and building control experts before recommending a private drainage solution. They should also ensure that a comprehensive site assessment is conducted at this stage. This task includes a soil porosity test and a trial hole.

The location of the product should be considered in accordance with the 2002 Building Regulations and great care should be taken over the final effluent disposal from the site.

To conclude, every building site should to be considered on its merits when choosing a sewage solution. Builders cannot afford to take chances when it comes to the efficiency and safety of the products they specify and install, and expert advice should always be sought in this complex and strictly regulated arena.

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