Guide Phosphates on the River Axe

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2. Nutrient neutrality and planning applications

River Axe SAC Catchment

The area affected is in the east part of the district that drains into the River Axe SAC catchment. These areas are subject to phosphate mitigation requirements. 

Area affected in East Devon 

View River Axe SAC Catchment map in full screen - best for mobile devices

Phosphate Budget Calculator

All planning applications must use the most up to date Natural England phosphate budget calculator. [Last updated May 2024]. This includes any current/pending applications.

The Levelling-up and Regeneration Act 2023 (LURA) created a new duty for water companies in designated catchments. This includes the River Axe. This duty will address pollution at source. The duty on water companies will ensure wastewater treatment works (WwTW) serving a population equivalent to or over 2,000 to meet specified nutrient removal at the Technically Achievable Limit (TAL) within the catchment by 2030. 

South West Water is required to upgrade Kilmington, Tatworth, and Colyton WwTWs before 1 April 2030. The calculator automatically reflects these specified nutrient removal standards from 1 April 2030.  

You should: 

  • use the calculator to find out the phosphate level for your proposal 
  • submit this information to support your planning application

You will need to re-run the phosphate budget calculations if you have a pending planning application which drains to one of the affected WwTWs. A planning application will only be able to proceed if: 

  • the proposed development is phosphate neutral 
  • you can identify and secure mitigation to make it neutral

The calculator contains help sections to assist with the stages of the process.  

Next steps

When you have used the calculator, you will have an understanding of how much mitigation a development will need. 

Small scale thresholds guidelines: These interim guidelines help to:

  • determine if a project will have a likely significant effect 
  • consider nutrient neutrality

If you wish to rely on these guidelines, you need to assess how the development accords with conditions a) to h).  A competent person with the relevant experience should do the assessment.  Please provide the completed assessment.  

If it can be demonstrated that a development meets all conditions, then it is likely the project can be screened from an Appropriate Assessment.  

Submission of an application 

The completion of the nutrient budget calculator and a Nutrient Neutrality Assessment and Mitigation Strategy (NNAMS) must be submitted with your application. It should be completed by a competent person with the relevant experience. A specialist ecological or environmental consultant will help you: 

  • complete the phosphate calculator 
  • research and design any required mitigation 

In order to ensure the most efficient processing of your application it is recommended that the application is also supported by a shadow Habitats Regulation Assessment (sHRA).  Please follow the link for a template example.

Natural England offer a Discretionary Advice Service which you could use and can help make the process more efficient by reviewing the proposed mitigation and sHRA to ensure it is likely to be HRA compliant. 

It is also recommended that any proposed mitigation that is novel or not a standard or recognised technique is evidenced by previously consented HRAs with reference to the planning reference number.  

Without the above information it is likely the planning submission will be delayed due to validating the technical information provided and requests for further information.  

There are currently no strategic nutrient mitigation solutions offered in the River Axe catchment. 

Sources of information

The Constructed Wetlands Hub is a joint site from the Rivers Trust and Constructed Wetland Association.  The site brings together a wealth of information and data on constructed wetlands. It provides useful information on how to design and find the best location for wetlands.  It only applies to 'treatment' wetlands.  It does not apply to informal wetlands e.g., farm wetlands and SuDS wetlands. 

The Framework Approach for Responding to Wetland Mitigation Proposals sets out: 

  • the design process
  • how to calculate nutrients mitigated by the wetlands 
  • what % of the modelled mitigation you can use from the outset

Natural England published: Introduction to Freshwater Wetlands for Improving Water Quality - JP044. The final section focuses on: 

  • integrated constructed wetlands (ICWs) 
  • the site-specific considerations that affect their design and implementation 

Construction Industry Research and Information Association (CIRIA) have published Using SuDS to reduce phosphorus in surface water runoff (C808F) and should be used to support the nutrient budget calculations.  

Susdrain also provides up-to-date guidance, information, case studies, videos, and photos that help to underpin the planning, design, approval, construction and maintenance of SuDS. 

Natural England have provided Information on Nature Based Solutions as Nutrient Mitigation (NBS2024) which includes a range of technical reports on nature-based solutions which potentially could be used to reduce nutrients. 

The Planning Advice Service (PAS) and surrounding Local Planning Authorities affected by nutrient neutrality can also provide information. 

Chemical dosing of package treatment plants 

Natural England have advised that PTPs requiring chemical dosing should only be used where it can be robustly justified and only if carried out by a British Water Accredited Service Technician. This also includes other suitably qualified professionals working for an established, experienced management company.  

Only iron dosed PTPs will be considered for large scale major developments whether other options have been evidenced to not be possible to achieve.  

Where chemical dosing is proposed, developers will need to provide a robust, evidenced justification: 

  • for why chemical dosing is necessary 
  • that dosing can be managed appropriately 
  • why a non-chemical (biological) PTP cannot be used

Where agreed chemical dosing is appropriate, developers will need to show that: 

  • a management plan for dosing and other maintenance is in place 
  • dosing will only be carried out by experienced, accredited professionals through a service agreement
  • this management will need to be legally secured in perpetuity (80-125 years) by a legal agreement for the lifetime of the development

These additional costs for management and maintenance of systems requiring dosing are likely to be prohibitively expensive for smaller developments.  Developers will need to provide: 

  • the make, model and capacity of the proposed PTP 
  • information on required dosing, management and maintenance