SITE PREPARATION (OFF-MAINS DRAINAGE & OFF-GRID ENERGY SUPPLY) STRUCTURAL COMPONENTS
legal changes brought in at the beginning of this year (2020) now mean that septic tanks can no longer discharge into surface water. The General Binding Rules state that if you own a septic tank that releases effluent directly into a ditch, stream, canal, river, surface water, or drain, then you either need to connect to the mains sewer, replace the tank with a sewage treatment plant, or create a drainage field that meets the current British Standard BS6297 2007.
OFF-MAINS DRAINAGE: OPTIONS Sewage treatment systems that deal with wastewater vary hugely in terms of how they work and their efficacy i.e. how effectively they can break down solids.
SEWAGE TREATMENT PLANTS The one product that works extremely effectively, wherever you live, is a sewage treatment plant (STP). A STP is an underground tank which provides an environment where aerobic bacteria can break down sewage and it is highly efficient, treating more than 90 per cent of the pollutants in wastewater. Packaged sewage treatment systems that have tertiary treatment such as packaged reed beds are the current ‘gold standard,’ bringing the efficiency rating up to 98 per cent. These produce a clear,
odourless overflow that is environmentally friendly and suitable for discharging even on sensitive sites, including into a watercourse (subject to Environment Agency/Environmental Protection Agency approval).
Contrary to popular belief, STPs don’t cost significantly more than septic tanks, if you compare both products in terms of installation and maintenance.
SEPTIC TANKS
A septic tank, by contrast, does not treat waste. It produces soluble waste from solids, and this is then discharged and filtered through the ground. This wastewater is not benign – it contains harmful bacteria. Indeed, under H2 Building Regulations, septic tank discharges are considered harmful and require a tertiary treatment option, such
as a reed bed, wherever a tank is installed.
Septic tanks can offer a serviceable solution for some homes, but they need both the right ground conditions, plus a reed bed, to work effectively. If a septic tank is installed in the wrong
location then it can pollute groundwater as well as streams, ponds and rivers. Moreover, if the ground conditions don’t allow efficient filtration (for example, if your house is built on clay soil or on an area subject to flooding) then the soluble waste effluent that the septic emits will collect near the surface, and sooner or later you will know about it. Testing the ground for its suitability to become a drainage field is usually done by a professional drainage engineer using a percolation test – the correct procedure is described in BS 6297:2007. It’s also worth noting that both H2 building regulations and BS 6297 state that the water table must be one metre below the septic tank outlet. If you are in any doubt as to the suitability of your garden to filter wastewater, then take the prudent course. Protect yourself and your family, by installing a sewage treatment plant.
Dave Vincent is commercial director at Kingspan Klargester
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www.sbhonline.co.uk
january 2020
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