Comment

Solent nitrogen neutrality: new guidance but no new solution

Nutrient neutrality has become a byword for frustration over the past year for housebuilders and others seeking to build in the Solent region. Concerns from Natural England over the deterioration of European protected sites in and around the Solent, due to eutrophication caused by excessive nutrient run-off, has led to a strict requirement for nutrient neutrality in order to achieve compliance with the Habitat Regulations.

This article was updated in November 2020, please click here to view the new version.

This applies to any new development that would increase the population through overnight stays, therefore relating to new homes, residential institutions, hotels and tourist attractions and accommodation. Many argue that other sectors, especially agriculture and the water industry, are far more responsible for the nutrient run-off that is affecting the Solent’s protected sites but nevertheless the development industry is being required to play its part too.

Therefore with much anticipation, Natural England has finally published its latest and newly revised guidance on this issue. The snappily titled Advice on Achieving Nutrient Neutrality for New Development in the Solent Region (Natural England, 2020), published in March, is now on its fourth version.

More detailed than previous versions, it has the benefit of bringing greater clarity on many aspects of this issue. The addition of river catchments plans clearly showing which areas are affected is one such example.

Calculating outputs from the Wastewater Treatment Works

A key change in the new guidance relates to the calculation of the Total Nitrogen derived from a proposed development that would exit the relevant Wastewater Treatment Works (‘WwTW’) after treatment. A new correction figure to take account of the amount of Total Nitrogen that can be present in river and groundwater, whilst still meeting the restoration objectives of the Solent’s protected sites, means that a further 2 mg/l can be taken away from a WwTW's Total Nitrogen permit level. This equates to a significant decrease in nitrogen outputs for some WwTWs that already have strict Total Nitrogen permit levels, particularly those of 15 mg/l or lower, meaning that development proposals will now have to provide less mitigation and may even become nitrogen neutral.

The new guidance also helpfully indicates that where there are known changes being made to a WwTW’s Total Nitrogen permit levels in the future, these can be taken into account when undertaking nitrogen budgeting exercises. This again has the potential to reduce the amount of mitigation that will be required.

Nevertheless, the issue that remains is for sites where sewage will flow to WwTWs which do not have a permit level for Total Nitrogen. These tend to be those WwTWs located inland, away from coastal locations. In the absence of a permit level and any accurate data on Total Nitrogen outputs, the advice when undertaking nitrogen budgets remains to use a figure of 27 mg/l to represent the Total Nitrogen concentration. However, what has changed is the 90% concentration limit applied to represent the level a WwTW can reasonably operate at without breaching its permit levels can no longer be applied where a WwTW does not have a Total Nitrogen permit. The 2 mg/l correction factor for background nitrogen, mentioned earlier, also has a proportionately much smaller impact in these cases because the Total Nitrogen concentration is already so high.

Consequently, sites which would utilise a WwTW that does not have a Total Nitrogen permit are going to generate some of the highest nitrogen outputs and therefore require very substantial mitigation. Thankfully, we are aware that the Environment Agency has concluded an agreement with Southern Water to monitor Total Nitrogen levels at these WwTWs. Hopefully it will not be too long until actual discharge data can be used in place of the high default 27 mg/l figure that gives rise to a huge level of mitigation being required.

Notwithstanding any voluntary monitoring arrangements agreed, this continues to highlight the need for a thorough review of nitrogen discharge permitting regimes for these affected WwTWs, so that a lower Total Nitrogen concentration figure can be demonstrated or actions can be agreed to achieve a lower concentration.

Package treatment plants

The latest guidance now incorporates a methodology for calculating the outputs from package treatment plants. This is of course helpful for those proposals that are unable to connect to the main sewer system. However, it would appear that Natural England remains sceptical of package treatment plants and looks to avoid them being used wherever possible. The guidance now establishes a need to provide demonstrable evidence of the efficiency of any package treatment plant. This will need to be in the form of monitoring data or lab test results; reliance on manufacturer claims will not be accepted. Whilst it is useful to have this guidance we note that unless they are particularly efficient at removing Total Nitrogen, the level of mitigation required from developments that use package treatment plants is going to be significant.

Mitigation

One area of guidance that has been lacking until now has been on how to approach mitigation for those developments that would generate a surplus of Total Nitrogen. A particularly welcome piece of guidance is the confirmation that mitigation land used to achieve nutrient neutrality can also be used to mitigate other adverse environmental effects, such as wildlife loss and flood management. This could be beneficial to those also seeking to demonstrate a net biodiversity gain from a proposal in light of the requirements from the Draft Environment Bill.

An area of difficulty regarding mitigation land has been demonstrating how this can be secured in the long-term. For on-site mitigation the guidance is clear that this can be secured as designated open space or through other legal mechanisms. For off-site options, the approach has generally been to require an appropriate change in ownership of the mitigation land to a Local Planning Authority on non-government organisation. However, the guidance now recognises that there may be other legal mechanisms available to secure the deliverability and enforceability of a mitigation proposal with Natural England being willing to consider these on a case by case basis. Although whether such an approach would be acceptable to a Local Planning Authority, in its role as competent authority, remains to be seen.

There is also crucial new guidance on the spatial and temporal principles behind which areas will be considered appropriate for providing mitigation land and which will not. These principles are based on a number of factors including being within the same river catchment, the spatial relationship with the relevant WwTW and European protected sites, and the local geology.

Final thoughts

This new guidance is to be welcomed and represents a significant step forward in helping those in the development industry understand how they can assess the nitrogen impacts of proposed development, and how to achieve nutrient neutrality for their affected proposals in and around the Solent region.

However, it is apparent that we now need action from Local Planning Authorities, the Partnership for South Hampshire, Natural England, the Environment Agency, Southern Water and others. We need to see effective measures to reduce output concentrations of Total Nitrogen from WwTWs and the delivery of appropriate and cost effective mitigation schemes to support those who cannot readily address their own nitrogen surplus. Only then can we start delivering the crucial development needed in the Solent region that has been massively delayed by this issue.

We provide regular updates on issues of nutrient neutrality and remain well placed to advise our clients and guide affected developments through the planning process. If this is something you feel we can help with please do not hesitate to contact Peter Home for an informal discussion of your needs, or to request a copy of the above Solent River catchments by SPA map.

9 April 2020