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Achieving Nutrient Neutrality through Septic Tank Replacement

November 2022

What is Nutrient Neutrality?
Within the last 2-years, Natural England have highlighted high levels of phosphate pollution in over 74no. local authority areas. Phosphates cause significant harm to the valuable ecosystems that the rivers support. Concerns surrounding this issue, together with case law established by a Court judgement (known as the Dutch N case), led Natural England to advise that new residential or agricultural developments should no longer be granted planning permission. The exception being if the applicants can demonstrate there would be no net increase in phosphates. This led to the term ‘nutrient neutrality’ being coined.

Since Natural England raised this issue there has been much debate about how to mitigate the phosphate impacts of new developments to allow stalled planning applications to be approved.

Now 2-years on, it appears progress is being made, with many new, approved solutions coming forward. 

Replacing septic tanks with package treatment plants
One of the most exciting and viable solutions is to offset phosphates generated by new development by replacing old septic tanks, with modern PTPs. Septic tanks are highly inefficient at removing phosphates compared to PTPs. Replacing septic tanks with PTPs can greatly reduce the amount of phosphates entering the environment through waste water. That reduction can provide credits to offset phosphates generated by new homes. 

Modern biological PTPs will generally remove adequate amount of phosphates from waste water to offset a small number of new dwellings. This can potentially be increased further through the application of chemical dosing to the PTP. However, Natural England and the Somerset Councils have confirmed that chemical dosing should only be used where no other option exists.

It is also important to note that under Environment Agency guidance, a new development should connect to a public foul sewer rather than a PTP where this is reasonably achievable.

Further information regarding the Somerset Councils’ approach to phosphate mitigation through replacing septic tanks with PTPs, as set out below:-
Advice Note – Considering Package TreatmenTanks as part of nutrients mitigation in Somerset

Key points
There is an opportunity to offset phosphate impacts by replacing septic tanks with modern package treatment plants (PTPs).

Natural England and the Somerset Councils have confirmed this approach is acceptable in certain circumstances as a way to release stalled sites across the county.

Greenslade Taylor Hunt has the knowledge and experience to advise on this.

Legal requirments for homeowners regarding septic tanks
Homeowners whose property drains to a private system, such as a septic tank, need to be aware of the ‘General Binding Rules’ set out by the Environment Agency. Most of these rules apply to all small sewage discharges, but some of the rules only apply to ‘new’ discharges that started, or changed, on or after 1st January 2015.

Further information is available at the following link, as set out below:-

Permits you need for septic tanks

Any septic tank that does not meet the ‘General Binding Rules’ must either be connected to a public foul sewer, if it is reasonable to do so, or changed or replaced so that it will meet these rules. If this is not feasible, then a special Environment Agency permit is needed to keep the system.

In particular, all septic tanks that discharge directly to a watercourse are now unlawful, and any such tanks must be replaced as soon as possible with a PTP or mains connection (or the discharge redirected to an appropriately located subsurface soakaway) as soon as possible.

More information is available, via the link, as set out below:-

General binding rules small sewage discharge to a surface water

But what are the benefits for homeowners?
Landowners, housebuilders and developers may be offering to upgrade or replace a homeowners existing septic tank or PTP, saving them a cost in the region of £10,000 - £15,000 depending on the capacity of the tank/plant.

It is often not possible for new development to achieve nutrient neutrality through on-site measures alone. This means they will often be reliant upon off-site measures, such as septic tank replacements.

Landowners, housebuilders and developers can offer a homeowners (within phosphate affected areas) a replacement modern PTP for FREE, to include future maintenance responsibilities, and in return, they will be able to use the resulting ‘phosphate credits’ to get their land released for development. 

This could be a win-win situation for both parties.

To see if your home is within a phosphate affect area, see the latest phosphates catchment area map, via the link, as set out as below:-

Phosphates Map - March 2022

Is this an approved solution?
Yes, it is. Natural England has, in principle, approved a number of phosphate mitigation solutions for residential development schemes within the Parrett and Axe catchments, where new 
housing can be demonstrated to be ‘nutrient neutral’ through the replacement of septic tanks with new PTPs. 

For example, Natural England has approved a phosphate mitigation solution for a residential development scheme of circa 100no. dwellings in South Somerset, falling within the River Axe catchment. The solution is to replace existing septic tanks, off-site, with PTPs, which provides a significant offset. As well as this, the proposed scheme will use PTP’s with a chemical dosing unit that will be adopted, managed and maintained by Albion Water.

As well as this, the Somerset Councils have now released an advice note regarding the details of approved mitigation proposals within the catchment, as set out above.

Is this solution future proof?
Mitigation through septic tank replacement may offer a much need long term solution. With Natural England’s approval of these mitigation schemes, residential development schemes may be released from the planning system and effectively kickstart schemes within areas affected by nutrient neutrality.

Get in touch
If you have a septic tank in a phosphate affected area and would be interested in discussing a free replacement, with all costs paid for, this would be a good time to seek further advice.

Greenslade Taylor Hunt’s Development Land and Planning department will continue to closely monitor Natural England and the Somerset Councils advice, so that we can provide our clients with the best advice. In doing so we aim to add value for our clients and increase the supply of much needed new homes. 

Please get in touch if you would like further information and advice regarding opportunities for providing nutrient offsetting solutions.

Mark Chugg , Partner, Head of Department | | 07738 426759

Graham Ford, Partner | | 07803 957157

Claire Alers-Hankey, Partner | | 07764 817730

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