Faraday Road, Kirkby Stephen - Achieving Nutrient Neutrality

Enviren delivered a successful nutrient neutrality strategy for a major residential development of 149 homes at Faraday Road, Kirkby Stephen. The solution avoids costly off-site land acquisition or wetland construction by using an integrated SuDS strategy and an advanced on-site treatment plant. As a result, the scheme is both compliant and deliverable, strengthening the developer’s planning case and reducing long-term risks.

Environmental & Regulatory Context

On 16 March 2022, Natural England advised that new development in the River Eden Special Area of Conservation catchment has the potential to cause adverse impacts due to nutrient pollution. Local authorities must ensure that new development does not increase nutrient loading before granting permission.

Both the surface water and foul water from the development drain to the River Eden catchment, meaning phosphorus neutrality is essential.

Existing Site Conditions

3.1 Land Use

The site currently consists of lowland grazing land, a rural agricultural baseline.

This land use typically has modest phosphorus export, which forms the baseline for the nutrient budget.



3.2 Ground Conditions (Soakaway Testing)

Supplementary ground investigation and BRE365 soakaway tests were completed in July 2025 across four trial pits (SA201–SA204).
Most tests showed good drainage characteristics and medium permeability, with infiltration rates up to 9.8 × 10⁻⁵ m/s.

These conditions support the feasibility of infiltration-based SuDS.

Proposed Development & SuDS Strategy

4.1 Development Overview

• 149 dwellings
• 7.760 ha total site area
• Hardstanding, roads, footpaths, and open space

4.2 SuDS Treatment Train

The NNAMS confirms a comprehensive SuDS strategy will be used, including:

• Swales
• Filter trenches
• A detention basin
• Sediment capture upstream of SuDS components

The SuDS design aligns with CIRIA C753/C808 guidelines.

4.3 Water Treatment via Package Treatment Plant (PTP)

A dedicated on-site Package Treatment Plant (PTP) is proposed. It will:

• Treat all foul water flow
• Be adopted by an OFWAT-regulated NAV
• Discharge to an adjacent watercourse

This is central to achieving nutrient neutrality.

Nutrient Budget Calculations

The Executive Summary states:

“This report demonstrates that the development will achieve Nutrient Neutrality through the incorporation of Sustainable Drainage Systems (SuDS) and the installation of an on-site Package Treatment Plant…”

The components contributing to neutrality include:

5.1 Surface Water Reductions

• Effective phosphorus removal through the SuDS treatment train
• Sediment capture features enhancing particulate P removal

5.2 Foul Water Reductions

• High-efficiency P reduction via the PTP prior to watercourse discharge
• NAV adoption ensures long-term operational compliance
  

Ground Investigation & Design Confidence

GEO Environmental Engineering’s works (September 2025) reconfirmed:

• The site is not affected by mining hazards
• The strata are predominantly Glacial Till over Penrith Sandstone
• No significant contamination risks were identified

The ground is therefore suitable for infiltration SuDS with localised construction considerations.

Conclusion

The NNAMS for Faraday Road, Kirkby Stephen demonstrates that:



Nutrient Neutrality is Achieved

Through:

• A robust SuDS treatment train
• An on-site, NAV-adopted Package Treatment Plant
• Positive infiltration characteristics across most of the site

No Off-Site Mitigation Is Required

The development is self-neutralising and satisfies Natural England’s requirements for the River Eden SAC.

Fully Compliant for Planning Purposes

The strategy directly addresses Cumberland Council’s requirement that new development must not increase phosphorus loading to protected habitats.