The various nutrient budget calculators which have been made available by affected LPA’s are based upon NE’s ‘Stodmarsh Guidance’ (for Kent, Hampshire Avon and Somerset), or the NE guidance that as been specifically developed for the Solent catchment (Hampshire, IOW, part of West Sussex) – both of which we are familiar with and use to create the nutrient budget assessment. Te LPA’s calculators are useful in providing the approximate nutrient budget for developments, but do not allow for adjustments such as on-site bioretention SuDS which can reduce the urban leaching rate by ~50%. Furthermore, whilst some of the calculators indicate an approximate area of wetland, woodland or other use that can be used for mitigation – they do not provide the crucial advice of where this would need to be located, or in the case of a wetland, the characteristics of the stream / river / catchment it would need to intercept to achieve the required nutrient reduction. Many applications have fallen down where space is allocated for a wetland as part of a development, but no thought has been given to the water that feeds it.

For those developments that cannot achieve neutrality without purchasing ‘nutrient credits’ from other developers (or the LPA’s, eventually), it may be worthwhile having a consultant conduct the assessment to ensure that the budget is minimised as far as possible (to reduce the amount of credits that need to be purchased).

Yes, but only regarding phosphorus, (Hampshire Avon, Somerset) – if you have no means of connecting to mains sewerage and have to use an on-site package treatment plant (PTP) connected to a drain field, then it may be possible to prove that the treated wastewater cannot reach the designated site. Somerset CC has produced a set of criteria that must be satisfied to prove this is the case (please refer to appendix B). Whilst this guidance has been produced by Somerset CC, it should also apply to the Hampshire Avon area as it has been approved by the NE Wessex team which covers both areas. It should be noted that a ground investigation will be required to help assess compliance with these criteria (and percolation testing will be required on site in any case to size the drainage field). However, having completed the ground investigation, if the exemption criteria cannot be met then a phosphate budget assessment and possible mitigation will be required.

No – this would be futile. Any water that enters the sewer, clean or dirty, produces the same quality of effluent at the outlet of the relevant sewage works. This is especially true of sewage works that dose coagulants as part of the phosphate treatment process. The coagulants are dosed according to demand in order to maintain a constant concentration at the point of discharge. If you reduce the phosphorus load entering the sewer, you help the water company save on coagulant but don’t provide any improvement to your phosphate budget.

Yes – It’s highly likely that the LPA’s will eventually introduce a ‘nutrient trading’ scheme as part of their strategy, whereby landowners can ‘sell’ credits that are generated by the creation of ‘interceptor wetlands’, woodland planting or wildflower meadows at strategic locations within the catchment. However, this may take some time to establish.

In the meantime, there is obviously an unofficial market based upon supply and demand. If you implement a scheme that benefits several other developers, then there is clearly a deal to be done. In terms of the value of credits, as an official market has yet to be established, they would obviously only be worth what the buyer is willing to pay.

It’s important to note that for any scheme, the amount of nutrients that can be offset – and the locations of the developments that would benefit – has to be verified by NE. This can be achieved by liaising with NE directly using their discretionary advice service (DAS) which is a paid for service.

Aside from negotiating on price, any transaction on the buying and selling of credits would have to be legally watertight such that all of the beneficiary developments remain indelibly linked to the mitigation scheme (which must be in place ‘in perpetuity’, i.e. for 80 – 120 years).

At the time of writing (Jan 2022) the nutrient neutrality ‘crisis’ has been going on for 18 – 30 months, depending on which area your development is located. It’s understood that all of the affected LPA’s are developing strategies, but it’s proving to be a long and frustrating process and we are not aware of any schemes that are fully developed yet, which would allow developers to purchase credits (or make contributions through CIL). Time is required for the LPA’s to negotiate with land owners and purchase potential mitigation sites. Even when they have secured the land, time is still required to implement mitigation schemes such as wetlands.

In the meantime, the most feasible and timely course of action would appear to be the provision of mitigation schemes by private entrepreneurs / landowners at strategic locations, which maximise both the number of nutrient credits and the number of potential beneficiaries.

No. The optimal mitigation schemes are those that minimise impact on current agricultural activities – as the rural economy relies on a healthy agriculture sector. ‘Interceptor wetlands’ on riparian land that extract and treat water from perennial streams and rivers are very effective in providing mitigation, with land-take being a lot less than woodland options. This is especially true for phosphorus, where the amount of land offsetting is significant. It typically takes 3 ha of cereal crops to be converted to woodland, just to offset 1 kg of phosphorus.

‘Retrofit SuDS’ (sustainable drainage systems) that intercept existing urban drainage systems with bioretention features can reduce the nitrogen and phosphorus loads from the contributing catchment by up to 50% and 80%, respectively. NE are very keen to see this kind of mitigation, especially as they deem urban runoff to be more polluting that agricultural runoff.

Prime locations for retrofit SuDS are land adjacent to existing car parks, or existing landscaping around large buildings where downpipes can be disconnected and re-routed through rain gardens.

This is a good question, another is “why do the nitrogen and phosphorus permits change between different sewage treatment works?”

The answer is that the water companies do already have their own legal obligations to reduce the amount of nitrogen and phosphorus entering the various affected catchments, as regulated by Ofwat and the EA through ‘WINEP’. Despite this, NE still require any new development to be nutrient neutral (with the burden of neutrality falling to the developer). NE’s ultimate goal is to reduce the nutrients entering the designated sites rather than just keep it at the current load – that’s the only way to improve the water quality from the current ‘unfavourable’ status.

The water companies’ improvement works are targeted at the locations where housing and development is likely to be greatest, so plants that serve large towns will have much lower permit consents than for the small rural plants.