Thinking of Replacing Your Septic Tank Under a Nutrient Mitigation Scheme? Here’s What Every Landowner Should Know
The sales pitch often sounds appealing:
“We’ll replace your old tank at no cost to you — and you will be helping the environment.”
However before you sign any documents, it’s vital to understand what these schemes actually involve, and the long-term legal obligations that could come with them.
🌿 What Are Nutrient Mitigation Schemes?
Under government and Natural England rules, new housing developments in certain catchment areas can’t go ahead unless they can offset their impact on nutrient pollution, particularly nitrogen and phosphorus entering rivers, wetlands, and protected sites.
To create those “offsets” (called nutrient neutrality credits), developers often partner with companies that install upgraded sewage treatment systems on private land.
The logic is simple: if an old septic tank is replaced with a high-efficiency sewage treatment plant that removes more nutrients, the resulting environmental benefit can be sold as a “credit” to developers.
So far, so green. But the legal mechanics behind these arrangements can be complex and risky if misunderstood.
⚖️ The Legal Framework: Section 106 Planning Obligations
Most of these schemes are formalised through a Section 106 Unilateral Undertaking, a legally binding agreement under the Town and Country Planning Act 1990.
When signed, it becomes a local land charge, registered against your property for up to 90 years. That means the obligations bind not only you but all future owners of your land.
Typical undertakings include:
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Keeping the sewage treatment plant in continuous operation for 90 years;
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Allowing council inspections and monitoring;
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Maintaining access for the installation company;
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Not removing or replacing the system without consent.
In short, once signed, you are committed, even if the plant no longer serves your property or the installer goes out of business.
💷 Who Benefits Financially?
The key question: who gets the “nutrient credits”?
Almost always, those credits are assigned to the installer or developer, not to the landowner.
That means:
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You don’t receive any direct payment for the environmental “value” your upgraded system generates;
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The developer uses those credits to unlock planning permission elsewhere;
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You remain responsible for the physical equipment and the obligations tied to it.
So while you might not pay upfront, you are effectively trading long-term control of part of your land in exchange for an installation that primarily benefits others.
🧾 Key Questions to Ask Before You Sign
If you are approached with such an offer, take the time to ask detailed questions. Here are the essentials:
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Who will own the sewage treatment plant once it’s installed?Will it belong to you or to the company?
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Who carries liability if the system fails or leaks?You could be legally responsible for pollution, even if you didn’t install it.
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Will the Section 106 agreement bind my title?Could it affect your ability to sell, remortgage, or develop your land?
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What happens if the company ceases trading?Who maintains the system or takes over the 90-year obligation?
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Are any neighbours connected to the same system?If so, you will need clear terms for shared maintenance, costs, and access.
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Do I lose any planning or environmental benefit by assigning the “nutrient credits”?
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Can I move or replace the system in future if it becomes obsolete?
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What are the annual maintenance costs, and who pays them?
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Is there an independent warranty or insurance policy in place?
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Can I see the full draft agreements before I commit?(You should and you should get independent legal advice on them.)
🧭 How These Agreements Affect Neighbours
If you share drainage arrangements, for example, if your neighbour is connected to your old cesspit, their rights may also be affected.
Replacing a cesspit with a private sewage treatment plant can extinguish or complicate shared drainage easements unless new rights are granted.
This can lead to disputes if not handled properly. The simplest solution is usually a short Deed of Confirmation of Easement, confirming that existing connection and maintenance rights carry over to the new system.
🏡 Protecting Yourself as a Landowner
If you are approached by a supplier or developer offering to install a treatment plant:
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Take your time.Don’t feel pressured to sign anything. Ask for all documents in writing.
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Get your own legal advice.A solicitor experienced in property and planning law can explain the risks and suggest amendments to protect you.
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Check your title plan.Make sure only the affected area is included in any planning obligation, and your other land is not accidentally bound.
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Ask for proof of insurance and warranties.The system should be covered for defects and environmental compliance.
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Confirm that your rights and boundaries remain intact.Including any access routes and shared drainage connections.
🧠 A Word of Caution
Many of these schemes are genuine, environmentally responsible initiatives, but they are also legally and financially complex.
A promise of a “free upgrade” can easily become a 90-year obligation that restricts what you can do with your land.
Before signing, always ensure:
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You understand who benefits and who carries the risk;
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You have written clarity on ownership and access; and
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You have had the agreements reviewed independently.
📞 Need Help Reviewing a Nutrient Mitigation Agreement?
If you have been approached by a supplier offering to replace your septic tank or cesspit under a nutrient mitigation or neutrality scheme, we can help you review the documents and protect your property interests before you sign.
Contact davidp@mjpconveyancing.com for clear, practical advice on:
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Section 106 Undertakings
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Easements and access rights
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Private drainage and maintenance obligations
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