“New” regulations governing the use of septic tanks come into force on January 1st 2020. David Stagg, technical product specialist for sustainable water management specialist Graf UK, talks specifiers through their options for compliance.
Architects designing properties off the mains sewage network need to be aware of this change which is a bid by the Environment Agency to reduce the level of pollution from sewage in the nation’s watercourses.
Under the General Binding Rules, anyone with a septic tank discharging into a watercourse must replace it or upgrade the foul water solution by this New Year, or sooner if the property is sold before this date.
The rules are:
- Use the correct treatment system – a septic tank or small sewage treatment plant – so the Environment Agency can assess the risk of using it in the location.
- The treatment plant must meet British Standard BS EN 12566.
- The treatment plant must be installed correctly and have enough capacity.
- The treatment system must be regularly emptied and maintained.
- If the property is sold, the new owner must be informed about the sewage treatment system.
- If use of the treatment system ceases, it must be properly decommissioned.
So, how can systems be replaced? There are five options available:
- If a mains sewer has become available, connect to it.
- If space is available, install a drainage field so the septic tank discharges into the ground.
- Replace the septic tank with a small sewage treatment plant.
- Upgrade an existing surface water discharging septic tank with a conversion unit. A permit is required and evidence provided that it will treat to the equivalent standard as a sewage treatment plant.
- In exceptional circumstances, a permit can be applied for to allow discharge to surface water.
To establish what you should do to ensure a treatment system meets the “new” rules, consider the following.
If the existing septic tank discharges to a drainage field that is correctly sized for the tank, then it is compliant but if it is not, then the correct size needs clarifying and equipment modified the meet the requirement.
If the existing septic tank discharges to a soakaway, watercourse, river or stream and there is space for a drainage field, then clarify the size of drainage field required and install it as the discharge point from the septic tank.
If there is not enough space for a drainage field, then the septic tank must be upgraded and if it cannot discharge into a local watercourse then a permit needs to be applied for it to discharge to a soakaway.
So, what’s all this going to cost? Well, the lowest cost long term is most likely to be to connect to a mains sewer if one has become available.
The next best cost is probably to install a new sewage treatment plant or a conversion unit to the existing septic tank, if allowed to do so. Either of these options is likely to start at somewhere around £2,000, based on the fact that a three-bedroomed house would need a minimum of a five-person treatment plant. Installation would be on top of this and varies greatly but could add a further £5,000 to £10,000.
A higher cost would be to install a drainage field if land is available and the soil conditions suitable. However, depending on its size, this may be similar to the cost of a new sewage treatment plant as many metres of perforated pipe might be needed which can mean a significant area of land has to be excavated.
It is difficult to put a sum on this as it depends on the percolation rate of the soil but it is not likely to be a small area to dig up and therefore the labour and plant hire alone is likely to cost more than some of the earlier options. Infiltration tunnels are a great alternative to traditional slotted pipe that takes up a great deal of land space but these will require a permit from the Environment Agency.
Last but not least – what to look for in a sewage treatment plant.
Specify one which controls effluent quality discharged while being efficient on energy consumption through the use of a sequence batch reactor process. One which can automatically adapt to a system becoming under or over-charged so performance is kept to a high standard and energy efficiency is not compromised.
One with a treatment process that results in a high-quality effluent discharge that far exceeds current regulations and is future-proofed for any regulation tightening (the British Standard of 20mg/l for biochemical oxygen demand, 30mg/l for suspended solids and 20mg/l for ammonia nitrogen). This means that under normal circumstances effluent can be discharged directly into a flowing watercourse although special environments, such as Areas of Outstanding Natural Beauty, may require a higher quality of treatment.
One with discreet manhole covers, that does not require concrete backfill, and has no electrical components within the tank as well as a long sludge storage period.
Then, not only will your client be compliant, they will also be certain of a cost-effective, low-maintenance future in waste water treatment!
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