Sewage and Wastewater Rules and Regulations
It used to be the case that if it was possible to connect to mains drainage, then this was your only option. However, the Environment Agency PPG4 now states that if a treatment system is proposed that offers a more sustainable solution to water management on the site, then it may be acceptable. This is a big consideration if you are building a house as if you have your own sewage treatment system you never have to pay sewerage charges for the life of the property.
The first rule for off-mains properties is that rainwater from roofs and yards and sewage; both grey water (sinks, baths, etc.) and black water (toilets) MUST be piped in totally separate systems.
Rainwater is usually disposed of by piping it directly to a ditch or stream, or by installing soakway pits in the garden. These are large underground holes filled with stones or the new 'crates' and the rainwater soaks away over time. This type of soakaway MUST NOT be used for sewage effluent.
All sewage must be treated so that it does not pose a danger to health. This is done by either a septic tank to foul soakaway drainage field, which further treats the sewage using aerobic soil bacteria, or by a sewage treatment plant which uses aerobic bacteria within the tank to treat it.
In order to be able to have a septic tank and soakaway system, you must prove that the soil is capable of soaking up the effluent even dung wet weather. This is done by undertaking Percolation Tests on the soil below the proposed drain level. Bedrock and the Water Table must not be within 1 metre of this test depth at any time of the year in order that there is enough soil depth to soak it away.
If the percolation tests fail or you have a high winter water table, then you can choose a sewage treatment plant that is allowed to discharge directly to a ditch or watercourse (or soakaway, if the perc. tests allow and you prefer a clean discharge). This is, in any case, usually the cheaper option as soakaways are very expensive to construct.
All underground sewage treatment plants under 50 person size MUST have been tested for 38 weeks at an EN Test Centre on the Continent and be fully EN 12566-3 2005 Certified as being fit for the purpose. ALWAYS check that it has been tested by visiting the list of tested plants on the PIA Website as some manufacturers will try to fool you and it is very easy to forge the Certificate.