Nutrient Neutrality

Addressing Phosphorus only for rural small-scale discharges (less than 2m³/day - typically less than approx. 5 dwellings) where there is no connection to mains foul.

This relates to those sites in rural areas where there are no riparian routes to watercourses, where connection to mains foul drainage is not possible, where Package Treatment Plants or Septic tanks (small discharge up to 2m³/day directly to ground) are proposed, where specific criteria are met (see a - h below) and to assist in concluding no likely significant effects in respect of Nutrient Neutrality from Phosphorus only. Anyone seeking to utilise this methodology should be aware that this does not deal with Nitrates which will also need to be mitigated and HRA demonstrated.

The Norfolk Authorities have commissioned a report (Royal Haskoning small scale discharges of Phosphorus: Low Risk Mapping) which follows and builds upon previously agreed interim guidelines between Natural England and Local Planning Authorities regarding small scale thresholds within the hydrological catchments of areas subject to nutrient neutrality guidance.

The guidance relates to small discharges from Package Treatment Plants (PTPs) and Septic Tanks (STs) of less than 2m³/day directly to ground and it states that where all the requirements of pre-defined conditions are met, a PTP / ST will not have a likely significant effect on the designated site from phosphorus. The small-scale thresholds only apply to phosphorus and not nitrogen, which is a more mobile nutrient.

Criteria a - h need to be satisfied for this approach for Phosphorous to apply.  Details of these conditions can be found at paragraph 2.2 of the report (link below)

A small sewage discharge low risk zone map has been created to support the identification of areas where small scale discharges for Phosphorus may be acceptable.   The map defines the areas which fall within the low-risk zone where all the requirements of conditions a, b, c, d, e and g are met.

Conditions f and h require site specific information and when provided alongside the mapping can be used to demonstrate that all the required conditions are met.

Where all the conditions (a to h) are met then Natural England can advise that, in its view, a conclusion of no Likely Significant Effects alone and in combination for phosphorus can be reached in these circumstances.  However, nitrogen mitigation will still be required.

For a PTP / ST to be accepted, it is expected that a technical report would need to be submitted which shows the location of the PTP / ST within the low-risk zone and any supporting evidence to demonstrate conditions f and h are met.

The PTP / ST must also be able to achieve the appropriate Building Regulations requirements. The building regulations state that a connection to the foul sewer should be considered to be potentially feasible where the distance from the development site to the sewer is less than the number of properties multiplied by 30m. In addition to Planning Permission and Building Regulation approval, an Environmental Permit from the Environment Agency may also be required.