Kevin Roe, sales director of Kingspan Klargester, looks at the drainage options available for different sites.
Of the country’s current stock of 25 million houses, around 1.5 million are not connected to the sewer. In all cases the first consideration should be a sewer connection and this may require using a pump station. This recommendation is in accordance with Building Regulations – pump stations are widely specified solutions for off-mains drainage.
If connection is impractical then a private drainage solution will be required. Assessment should include a site inspection by a suitably qualified expert before the preferred option is decided upon, as recommended by the 2010 Building Regulations and the DETR report 3/99.
An incorrectly specified solution can leave the property owner with failing toilets and drains. It also leaves them and the builder at risk of prosecution under The Public Health Act 1936.
Pump stations
A pump station must comply with both British Standards BS EN752 and Building Regulations for Foul Drainage with a mandatory capacity to hold waste for 24 hours should power supplies fail. Pump stations require careful design to offer the requisite storage and meet the requirements of the particular application. For further advice we recommend you contact a reputable manufacturer.
Private drainage options
If it is not possible to pump to the main sewer, generally determined by distance and access, then sewage will need to be dealt with within the boundaries of the property.
There are a range of sewage treatment systems to choose from, each with an efficiency rating based on how effectively they break down the sewage.
Septic tanks allow the settlement, storage and partial decomposition of solids, but they don’t treat sewage and need a drainage field or ‘soakaway’ into which the effluent can be discharged and filtered. Under H2 Building Regulations, septic tank effluent is considered harmful and, when installed, there should also be secondary treatment, including reed beds.
The DETR report recommends that septic tanks should only be considered if a sewer connection or a treatment plant cannot be used.
Sewage treatment plants (STPs) provide an environment where aerobic bacteria cultivate and break down sewage. They are highly efficient, treating more than 90 per cent of the pollutants.
Packaged sewage treatment systems, with tertiary treatment such as packaged reed beds, are the current ‘gold standard’, bringing the efficiency rating up to 98 per cent. They produce a clear overflow that is environmentally friendly and suitable for discharging even on sensitive sites.
Site suitability
The Regulations recommend a site assessment prior to installation, part of which should include testing the ground for its suitability as a drainage field, done as a percolation test; the correct procedure is described in BS6297:2007.
Sites on poorly draining soil or on areas subject to flooding will have poor soakaway characteristics leading to a high risk of local pollution and potential health issues for the site.
Both H2 Building Regulations and BS6297 state that the water table must be one metre below the septic tank outlet.
In these instances, an STP is your only option – and it’s worth noting that the life of the drainage field will be greatly extended because of the high effluent quality.
Effluent from an STP is allowed to discharge into a watercourse, but this is regulated and requires registration with the Environment Agency/Environmental Protection Agency. Applications for discharges can be made online, but always seek advice first.
Cost comparisons
Despite their high efficiency rating, STPs don’t cost significantly more to buy and install than a septic tank, particularly when the former does not require a drainage field. Maintenance and running costs are relatively low.