This article authored by Dr Gabriel Connor Streich originally appeared in the HRA Journal  

Introduction

Following the ‘Dutch Nitrogen Case’[1], a landmark ruling in the Court of Justice of the European Union (CJEU), Natural England received legal advice that changed how Habitat Regulations Assessments (HRAs) need to consider the impact of nutrient pollution to Habitats Sites. Where failure to meet nutrient water quality targets for nitrogen (N) and/or phosphorus (P) is contributing to a Habitats Site being in unfavourable condition, any plan or project that will result in an increase in nutrient inputs to the site cannot be consented without nutrient mitigation. Plans and projects thus need to show, through an Appropriate Assessment (AA), how they have calculated whether the plan or project will increase nutrient inputs to an affected site using a nutrient budget (in kgs of N and P) to show if the plan or project requires mitigation. If mitigation is required, the AA needs to show how these nutrients will be mitigated to remove the risk of Adverse Effects on Integrity. The mitigation of a nutrient budget associated with a plan or project will mean it achieves Nutrient Neutrality (NN).

There are a number of different mitigation techniques that are being deployed to help plans and projects achieve NN in affected areas. Mitigation techniques can be broadly divided into onsite measures, including sustainable drainage systems (SuDS) and water efficiency measures, and offsite measures, including wetlands, fallowing agricultural land and other rural land management techniques. Most NN practitioners are looking to Nature-based Solutions (NbS) to deliver nutrient mitigation, with NN providing a new mechanism to support the deployment of NbS schemes that also deliver a variety of additional environmental benefits.  

NN is currently affecting 27 waterbody catchments in England and six catchments in Wales. These water bodies are a mix of rivers, lakes, wetlands and coastal waters, and range in size from ~170 ha (the West Midlands Meres and Mosses Special Area of Conservation (SAC)) up to 340,000 ha (the combined catchment of the Solent Marine Habitats Sites). Many of the larger catchments contain significant urban settlements, including Norwich in the Norfolk Broads catchment, the numerous towns in the Tees Valley and the majority of Somerset’s largest towns. These 33 catchments intersect with the jurisdictions of 68 English Local Planning Authorities (LPAs) and 21 Welsh LPAs (Figure 1). Within these LPA areas, significant barriers have been placed on the ability to grant planning consent to new development due to the difficulties in delivering robust nutrient mitigation strategies, with the impacts being felt most acutely in the residential development sector. Current estimates suggest that in England, over 120,000 new homes are now stalled in the planning system due to NN[2].

Figure 1: Map showing the catchment areas and LPAs affected by NN in England and Wales.    

The impact of NN on housebuilding is multifaceted but it is in part due to difficulties in quantifying the amount of N and P mitigation that both onsite and offsite mitigation measures can deliver. These mitigation measures are not new or high tech, but previous applications have rarely quantified the kgs of N and P that have been taken out of the environment by their deployment. This has resulted in a slow response to NN in affected areas: Canterbury and Ashford LPAs have been grappling with NN in the Stodmarsh SAC catchment for over three years and development is still largely on hold in this area. Enter the Levelling Up and Regeneration Bill (LURB). Following the March 2022 expansion of NN to a further 20 catchments in England, there was significant fallout as the number of stalled housing developments increased. Part of the Government’s response was to introduce two amendments to the LURB aimed at reducing the amount of nutrient mitigation that new development in affected areas will require. These amendments have wide-ranging implications for the response to NN, some of which are inextricably linked to HRA compliance. This article will explore some of these implications and their associated risks. The focus here is on England as the LURB amendments do not apply in Wales, where Natural Resources Wales and Dwr Cymru Welsh Water have taken a different tac (this is another story for another day…)

The Levelling Up Bill - a sledgehammer to crack a (big) nut?

Before we get into the nitty gritty of the LURB amendments, it is worth establishing two key facts:

1. For most new residential developments, the main source of nutrients comes from the discharge of additional treated sewage effluent that is created by population growth as people occupy new houses (and flush their toilets).
2. Although there is a need to consider the risks posed by new nutrient inputs to impacted water bodies, the contribution of nutrient inputs from new housing is small in comparison to the existing burden of nutrient inputs from sewage treatment.  

The LURB has two key amendments with relevance to NN: amendment numbers NC77 and NS1, which have now become Part 7 of the bill, clauses 153, 154 and 155. NC77 is better known as the wastewater treatment works (WwTWs) Technically Achievable Limits (TAL) amendment. This states that all WwTWs serving 2000 or more people and in areas currently affected by Nutrient Neutrality need to be upgraded to TAL for N and/or P removal by 2030. For WwTWs that serve between 250 and 2000 people, upgrades may be needed at the discretion / direction of the Secretary of State. In practical terms, this means that WwTWs being caught by the TAL amendments need to be upgraded so that the treated effluent they discharge has a concentration of 0.25 mg P/L and/or 10 mg N/L. And as the main source of nutrients from new development is from treated sewage effluent, reducing the concentration of this effluent thus reduces the amount of mitigation new dwellings will require. It’s worth noting that of the 27 affected catchments in England, 3 have N as the nutrient of concern, 11 require developments to mitigate for N and P, and 13 have P as the nutrient of concern. The TAL amendment requires water companies to upgrade WwTWs to improve nutrient removal only for the nutrient of concern in each affected catchment area.  

Amendment NS1 is amending the Habitat Regulations to effectively say that when you are doing a Habitats Regulations Assessment (HRA) involving Nutrient Neutrality prior to 2030, you can rely on the upgrade to TAL at a WwTW being delivered by “the upgrade date” (for currently affected catchments this is 1 April 2030). Taken together, LURB amendments NC77 and NS1 mean that new developments connecting to WwTWs serving > 2000 people can assume that from 2030, they need much less mitigation. This brings us to one of the first issues with the LURB NN amendments: most of the stakeholders impacted by NN are assuming that the Bill and these amendments will pass in their current form. This big 2030 reduction in mitigation requirements is being priced into thinking on NN across the development sector and at Natural England (NE). The LURB is currently at Report Stage in the Lords, and it seems likely it will pass as is, but there is a huge risk if it doesn’t. This risk is especially significant to NE, who (I assume at the behest of Defra) are factoring in the impacts of the LURB into their NN strategy. For the rest of this article, I’ll be thinking about the potential impacts of the LURB amendments on the assumption that the Bill gains Royal Assent without further amendments related to NN, but it is worth considering the implications of this assumption not being met.      

One of the other key LURB issues related to NN is that it is a rather blunt force instrument. As stated above, new housing contributes, relatively speaking, a small proportion of the overall nutrient impact from treated sewage. Between 2000 and 2010, the Environment Agency conducted a Review of Consents (RoC) that assessed the impact of WwTW effluent discharges on Natura 2000 sites. This exercise used monitoring and modelling to determine whether a specific WwTW was resulting in a large water quality impact on a Habitats Site. New permits that reduced nutrient outputs from WwTWs were then enforced based on evidence from the RoC. Whether the RoC delivered to the extent it needed to is a debate I’m not getting into here, however the principle of the RoC – using evidence to determine policy – is conspicuously absent from the LURB TAL amendments, with a range of potential consequences.  

The LURB TAL amendment deadline

Upgrades to WwTWs resulting from the LURB are required to be delivered by 2030. Assuming that the LURB passes following the 2023 summer recess, this leaves just over six years for water companies to deliver the required WwTWs upgrades. Greenshank Environmental has previously analysed the scale of the challenge this poses to water companies[1], who normally plan investment in WwTW upgrades (and other work programmes) in 5-year cycles known as the Asset Management Planning (AMP) cycle. We are currently in the 7th of these cycles (AMP7). In AMP7, 32 WwTWs in areas affected by NN are being upgraded to have tighter P permits (4 of these permits are going to TAL). Looking only at the WwTWs that serve populations > 2000, water companies will need to deliver 128 upgrade programmes in the next AMP cycle (which starts in 2025). This is a four-fold increase on what they are delivering in the affected catchment areas in AMP7.

It is also important to note that all of the 32 WwTWs that are getting upgraded in AMP7 are getting P permit upgrades. There are no planned N stripping upgrades in the affected catchment areas in AMP7. Furthermore, there are only 12 WwTWs with N stripping technology out of at least 231 WwTWs in catchments where N is a problem nutrient. 11 of these WwTWs are in the Solent catchment (the other is in Poole Harbour). This adds an extra geographical component to the requirements on water companies, with those companies in N affected catchments potentially having an even greater requirement to deliver WwTW upgrades. This issue is especially pertinent for Northumbrian Water in the River Tees catchment, and Anglian Water in the Broads and Wensum catchments, which are catchment areas that need N mitigation, have large development pressures and no WwTWs that currently have N stripping technologies.

There is both a huge financial and logistical challenge associated with delivering the upgrade works required by the LURB. The estimated cost across all affected water companies is not clear, however I have heard anecdotally that Wessex Water have estimated costs of over £1bn required to meet their LURB requirements. Wessex Water have also noted that WwTWs upgrades cost £31,000 per tonne of N removed, which is significantly more costly than other NbS approaches[2]. Water UK, the water sector industry body, have also suggested that costs associated with the LURB will be passed on to customers with increases of £40 per year to water bills[3]. This is coming at a time when water companies have just pledged £10bn in additional investment to tackle sewage spills, with this money coming through water bill increases[4], and when water companies balance sheets will be under scrutiny as Thames Water faces potential collapse and renationalisation due to an unsustainable debt burden[5]. As the LURB has yet to pass, the costs associated with delivering the TAL amendments is a large financial uncertainty for water companies and the funding of these works should not be taken for granted.

The logistical challenge associated with delivering the upgrades is also massive. Each upgrade is a multimillion-pound, multi-year programme of work involving a wide array of specialists from multiple sectors. Normally planning for these upgrades happens through a regulated, multi-year business planning process, the current iteration of which is due to complete in 2024. Shoehorning the TAL amendment requirements into the water companies’ 2025 business plans if/when the LURB passes will be no mean feat. All of this points to a real risk that at least some of the TAL amendments will not be delivered by 2030.    

Figure 2: Highlighting the cost of WwTW upgrade works. Source: Southern Water, 2022.

You will remember that one of the amendments to the LURB allows for HRAs of new developments to assume that TAL upgrades will be delivered by the 2030 deadline. Practically, this means that a development may need a higher amount of nutrient mitigation up to 2030 and then a much lower amount post-2030. Most of the stakeholders affected by NN are working to this assumption, but what if an upgrade is not delivered in time? Housing developers will most likely have discharged any requirements related to an HRA and will have reached a legal agreement with the LPA (and  Competent Authority) around mitigation provision through Section 106. My experience to date suggests no developer will sign up to an S106 agreement that binds them to having to do more mitigation if a water company misses the LURB deadline for a TAL upgrade. So where does the buck stop? Does the LPA, as the Competent Authority, end up being responsible to rapidly find more mitigation and to be in breach of the Habitat Regulations until they do?

These are open questions which may not come to pass but given the potential risks associated with under delivery of the TAL amendment, it seems we should have conversation about how to manage this risk. And one significant risk mitigation approach would be to look at alternatives to ‘grey’ infrastructure solutions.

Swapping grey for green

Water UK have highlighted that the TAL amendment will commit water companies to investing in ‘concrete and steel’ as their response to tackle NN5. They also suggest that taking a green, catchment-based approach could see the sector provide up to £50m per year in funding to landowners and farmers to deliver NbS nutrient mitigation schemes and that committing the water sector to a grey infrastructure approach to NN shuts the door on the sector investing in green solutions. Water UK also highlights that green solutions have the potential to be delivered far faster than WwTW upgrades, allowing for the housing impasse in affected areas to be tackled far sooner. Whether the £50m in funding for catchment-based solutions to NN would actually be delivered is open to interpretation but the statements from Water UK highlight that another approach to delivering NN is possible and has the potential to deliver far more bang for its buck.

As mentioned above, there is a lack of evidence behind which WwTWs are being selected for upgrades due to the LURB. Greenshank’s analysis3suggests that there are at least 43 WwTWs in affected areas that currently have no nutrient permits and serve populations > 2000, i.e., will be slated for a TAL upgrade. These WwTWs have huge potential as locations for the deployment of strategic wetland schemes that could provide a significant contribution to the amount of mitigation that might be needed in a given catchment area, while also delivering a host of other environmental benefits associated with wetland creation. The first wetland scheme in the country that has been deployed to provide P mitigation in response to NN is now operational in Herefordshire[1]. This wetland has been constructed to provide additional treatment to effluent from the Luston WwTW, which is a small works serving a population < 2000. The Luston wetland has been certified as delivering around 280 kg P/year of mitigation, which provides a significant contribution to the mitigation requirements of new development in the affected areas of Herefordshire. This scheme was the first of its kind and took around 2 years to deliver. Since its delivery, the regulatory landscape has improved and there are now fewer barriers to wetland deployment for the purposes of nutrient mitigation[2]. Larger wetlands deployed at larger WwTWs could thus be key solutions with the potential to unblock backlogs in housing where they are viable in far less time than it will take to deliver TAL upgrades.

Wetlands (Figure 3) have become a favoured nutrient mitigation solution in the response to NN because, assuming you have a consistent nutrient input source, you can use an engineering approach to estimate the nutrient mitigation benefit the scheme will deliver with sufficient certainty to pass an HRA, thus justifying investment in a wetland. NE have recently released a framework to guide the production of wetland proposals[3], helping to add confidence that wetland schemes can be delivered with the required scientific certainty. However, while wetlands can provide strategic solutions to nutrient mitigation, finding suitable locations for wetland deployment can be difficult.

Figure 3: The Norfolk Rivers Trust Integrated Constructed Wetland treating effluent from the Ingoldisthorpe WwTW and benefiting the River Ingol. Source, Norfolk River Trust and William Morfoot, no date.

Wetlands have had a lot of attention from NN practitioners but probably the most widely applied nutrient mitigation solution is fallowing agricultural land. The Solent region has a functioning N mitigation market that is made up largely of private mitigation providers who are selling N ‘credits’ that have been generated by taking land out of agricultural production. From an HRA perspective, the benefit of fallowing mitigation schemes is that they pass the scientific certainty test with relative ease. Agricultural activities are sources of nutrients to the environment, so by stopping them you stop a source of nutrients to the environment and provide mitigation. However, fallowing schemes have an array of problems. The amount of P that comes from agriculture is, on a per hectare basis, a lot lower than the amount of P that is generated by sewage from new housing (this is true in most cases, but some types of farming in certain locations are an exception to this rule). Thus, using fallowing schemes in catchments affected by P requires an amount of land that is both unsustainable in terms of food production and non-viable in terms of cost. The relative amount of N that comes from farming compared with N in sewage does not completely preclude fallowing as a mitigation strategy in most cases, but there will come a point where the land take becomes unsustainable. Given current pressures on food security, food price inflation and rural economies, there is also a moral question as to the acceptability of taking otherwise productive farmland out of production to enable housebuilding. It should also be noted that 24 of the 27 catchments affected by NN in England require P mitigation, so there are also limited NN areas in England where fallowing can provide a meaningful contribution to mitigation requirements.

This begs the question of what other tools may be available in the nutrient mitigation toolbox? I previously mentioned SuDS, which should be looked at part of a mitigation strategy for any development. Recent guidance from CIRIA[1] (commissioned by NE) now means SuDS designers can attribute P removal efficiencies to different SuDS features with the confidence that these efficiencies have the requisite scientific certainty for use in an HRA. This will help to reduce the mitigation requirements for new developments, but even with a very good SuDS design there is still likely to be a residual amount of nutrients that require offsite mitigation, especially on larger development sites. Other offsite solutions now being proposed include various measures that have been in use for some time as part of the suite of catchment-based approaches to managing the water environment. Of these potential solutions, riparian buffers, engineered log jams / beaver dam analogues (BDAs) and drainage ditch management seem to have the most promise.

One of the challenges with nutrient mitigation for NN is that a development’s nutrient budget provides a specific amount of N and/or P that needs to be mitigated in units of kg/year. This means mitigation strategies need to be able to show that the chosen mitigation measures can deliver the required amount of mitigation at the HRA stage. As most developers, or indeed LPAs, will not be willing to speculate on whether a mitigation measure will deliver the mitigation they need by just getting something in the ground and monitoring it, there is a need for robust approaches to quantifying the mitigation potential of a measure before the fact. For wetlands, this can be done using an engineering  

approach. Fallowing schemes use nutrient export coefficients associated with different types of agriculture and environmental conditions. SuDS have percentage efficiencies (for P, with guidance forthcoming for N) that have been given to different types of SuDS feature.      

This latter approach has the most potential for catchment-based nutrient mitigation solutions. Riparian buffers are well-established methods for managing diffuse pollution sources in agricultural landscapes, with a significant body of peer reviewed academic literature from which percentage nutrient removal efficiencies can be drawn. BDAs and drainage ditch management have seen very limited deployment in the UK but are much more widely applied in the USA. Research from American studies of drainage ditch management for nutrient removal highlight the potential of this approach as a nutrient mitigation measure. Research on BDAs is still focussed more on their ecological and geomorphic impacts, however there is a larger body of academic work supporting the impact of beaver dams on reducing nutrient transport in river systems. Nutrient mitigation schemes need to be secured for 80+ years to meet the in perpetuity requirements that are part of HRA compliance for NN, which makes recommending beaver reintroduction problematic as a nutrient mitigation approach. Hence BDAs, which replicate the nutrient removal processes caused by beaver dams, are a useful surrogate. These solutions are currently being tested with NE to determine nutrient removal efficiencies that can be attributed to them, with the watchword in this process being ‘precautionary’ to ensure that the proposed nutrient removal efficiencies do not overestimate the potential benefit of these solutions.  

Figure 4: A Beaver Dam Analogue (BDA) in the USA. Source: NM Political Report, 2022.

Greenshank Environmental are in the process of submitting mitigation proposals that use combinations of riparian buffers, BDAs and drainage ditch management to develop nutrient mitigation schemes with low land take, minimal engineering requirements and that are relatively cheap and quick to deploy. These mitigation schemes, if/when they are signed off, will be the first of their kind nationally and we hope they will pave the way to being able to take an integrated catchment management approach to delivering nutrient mitigation schemes at scale. Given the potential range of issues with delivery of the LURB TAL amendments, it is clear that we need a wider toolbox of mitigation solutions that have the certainty behind them to be relied on through an HRA. I’m hopeful that soon this toolbox will have some more tools in that can help us to solve the NN crisis.        

Where the Levelling Up Bill will fall short

A final consideration of the impacts of the LURB TAL amendments should be given to the WwTWs which serve populations < 2000 and thus will only be upgraded at the Secretary of State’s discretion. Greenshank’s analysis suggests these works make up around 74% of the total number of WwTWs in NN affected areas. These small WwTWs are also the least likely to have existing nutrient stripping technologies, meaning that developments connecting to them need more mitigation per house than developments connecting to WwTWs that currently have or are being upgraded to have nutrient stripping. TAL upgrade programmes at larger WwTWs are likely to suck water company resources away from these smaller works and because mitigation schemes can service far more houses where a WwTW has nutrient stripping, private mitigation providers are more likely to sell mitigation to developments connecting to these WwTWs. This may result in development blackspots in rural areas where development may otherwise be viable and needed, with a disproportionate impact on small rural developers and rural economies.

The solution to this problem is to have a suite of mitigation measures that can pass the scrutiny of an HRA and that can be distributed around the rural landscape. Because riparian buffers, BDAs and drainage ditch management are deployed either along watercourses or in agricultural drainage ditches, both of which are ubiquitous in agricultural areas, these mitigation measures have the potential to provide a significant contribution to the nutrient mitigation challenge in development blackspots that may result from the LURB. Showing how these methods can be prescribed with sufficient certainty is thus even more important.    

Conclusion

The LURB TAL amendments will have a range of consequences on the delivery of NN, assuming that they pass into law later this year. The biggest immediate consequence is that, based on the wording of the legislation, HRAs of new developments in NN affected areas can start to rely on reductions in their mitigation requirements due to WwTW upgrades that should be delivered by 2030. There seems to have been little attention paid to the scale of the challenge that the TAL amendment upgrade programme will place on water companies. And there has been even less attention paid to what happens if water companies miss the 2030 deadline for completing TAL upgrade works while in the intervening period, Competent Authorities have been signing off HRAs under the assumption that TAL upgrades will be delivered and housing developments will need far less mitigation post-2030. Clearly there is a need to consider contingency planning in the event that TAL upgrades to WwTWs are not completed on time. Furthermore, there is a need to consider whether a blanket upgrade programme across all WwTWs serving populations > 2000 people (which is quite a low size threshold) is a proportionate response to the issue and whether there are alternative approaches that could deliver the required nutrient mitigation without pouring lots of concrete at significant cost to people’s water bills.

Alternative solutions to delivering the nutrient mitigation required to tackle the NN crisis are available and these solutions are green, not grey, with a range additional environmental benefits beyond nutrient removal. We have already had guidance and frameworks for the deployment of SuDS and wetlands that form part of the toolbox of mitigation measures we have available to deliver nutrient mitigation with the required scientific certainty. However, these solutions are potentially not enough to unblock the impasse in housebuilding that has been seen in areas affected by NN. Other catchment-based approaches to managing water in agricultural environments are needed to widen the opportunities for delivering environmentally friendly nutrient mitigation at scale. Riparian buffers, engineered log jams / BDAs and drainage ditch management are a suite of measures that have lots of deployment opportunities across agricultural landscapes and can be integrated with agricultural operations. Greenshank is actively working on projects that should see the first deployments of these techniques and we are hopeful that these approaches could provide a large contribution to the national requirements for nutrient mitigation to support NN.

The LURB TAL amendments are not going to result in upgrades to the majority of WwTWs in areas affected by NN because most WwTWs are below the size threshold for a TAL upgrade. New development tends to cluster around existing larger settlements, so the TAL amendments are likely to cover the majority of new housing, but where TAL upgrades are not happening may lead to development blackspots where new housing needs more mitigation per house and mitigation provision is lacking. These blackspots are likely to be in rural areas, disadvantaging small developers and rural economies. Having a suite of catchment-based approaches to nutrient mitigation that can be deployed across rural areas is thus even more important to ensure that the LURB TAL amendments do not have the perverse effect of levelling down in certain areas.    

References 1 Joined Cases C-293/17 and C-294/17 2 https://www.hbf.co.uk/news/nutrient-neutrality-lichfields-reportunblocking-homebuilding/ 3 https://greenshank-environmental.com/blog/f/is-the-levellingup-bill-heading-up-a-creek-without-a-paddle 4 https://greenallianceblog.org.uk/2023/01/13/the-levelling-up-bill -will-stall-water-company-investment-in-nature-recovery/ 5 https://www.water.org.uk/news-item/levelling-up-regenerationbill/ 6 https://www.theguardian.com/environment/2023/may/18/ english-water-firms-must-be-held-to-investment-pledge-saycampaigners 7 https://www.ft.com/content/deaf19d6-8da1-4241-a1e6- 2635535de88e 8 https://councillors.herefordshire.gov.uk/ ieDecisionDetails.aspx?Id=8974 9 https://www.gov.uk/government/publications/using-wetlands-to -improve-treated-effluent-discharge-rps-260/using-wetlands-toimprove-treated-effluent-discharge-rps-260 10 Johnson, D., Mcinnes, R., Simpson, M., Rose, G., Roberts, D., Sweaney, G., & Mcilwraith, C. (2022). Framework Approach for Responding to Wetland Mitigation Proposals. 11 Bradley, J., Haygarth, P., Stachrya, K., & Williams, P. (2022). Using SuDS to reduce phosphorus in surface water runoff (C808 ed.). CIRIA.  

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