Enviren - Planning Consultants

Station Road, Crewkerne - Achieving Phosphorus Nutrient Neutrality

Fri, 21 Nov 2025 03:45:14 GMT

Site & Development Overview

The report establishes the following key facts:

Site area: 16.532 ha
Land use: Arable farmland (pre-development)
Proposed development: 325 dwellings + associated infrastructure
Nutrient considered: Phosphorus (Total Phosphorus, TP)
Catchments:
Surface water → River Parrett
Foul water → River Parrett

Because both foul and surface water ultimately drain toward the sensitive Ramsar site, a full Habitats Regulations Assessment (HRA)–compliant nutrient budget is required.

Baseline Conditions

Nutrient Budget Calculation

Off-Site Mitigation Through P-Credit Acquisition

Conclusion of the NNAMS

The report concludes:

“The applicant shall achieve Nutrient Neutrality through the proposals and therefore nutrient arisings should not prevent planning permission being granted.”

The existing site consists of general arable land, which currently generates a baseline phosphorus export level typical of agricultural settings. However, the introduction of new dwellings inevitably results in:

Increased foul water discharge
Additional surface water runoff phosphorus loads

The NNAMS recognises this and calculates the predicted increase in TP load from development.

To eliminate the residual nutrient load, the applicant will acquire third-party phosphorus credits.

From the NNAMS Mitigation section:

Credits will be purchased for the full pre- and post-LURA nutrient loads, ensuring neutrality under both operational scenarios.

Post-Mitigation Outcome

After applying the purchased mitigation credits:

Total annual nutrient load (Pre-LURA): –0.00 kg/year
Total annual nutrient load (Post-LURA): –0.00 kg/year

This confirms full nutrient neutrality beyond reasonable scientific doubt.

Using Natural England-aligned methodologies, the development’s phosphorus budget is calculated. Key outcomes include:

Pre-Mitigation Nutrient Load

+33.10 kg TP/year (Pre-LURA)
+6.56 kg TP/year (Post-LURA)

(LURA = Likely Upgrades to Reduce Phosphorus at sewage treatment works)

SuDS Treatment Capacity

The scheme incorporates a full Sustainable Drainage Systems (SuDS) treatment train.

On-site SuDS can treat both dissolved and particulate phosphorus,
But surface water treatment alone cannot fully neutralise the development’s overall phosphorus load,
Remaining phosphorus after SuDS treatment = 0.08 kg/year, which must be mitigated off-site.

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Crewkerne

2025

The Enviren Nutrient Neutrality Assessment & Mitigation Strategy (NNAMS) was prepared to support a major residential development of 325 dwellings off Station Road, Crewkerne, Somerset. The scheme sits entirely within the River Parrett hydrological catchment, meaning it is subject to stringent requirements introduced following Natural England’s 2020 advice note on excessive phosphorus entering the Somerset Levels and Moors Ramsar Site.

This case study summarises how the development achieves full nutrient neutrality through a robust assessment and targeted mitigation approach, based directly on the submitted NNAMS.

Why This Scheme Is a Strong Example

This project demonstrates:

Robust, transparent nutrient budgeting

The phosphorus calculations follow Natural England guidance and incorporate both foul and surface water pathways.

Effective SuDS integration

The design includes infiltration-based systems, with confirmation of appropriate soils and groundwater levels.

Full offsetting of residual phosphorus

Off-site credits remove any remaining nutrient burden.

Compliance with Habitats Regulations

The mitigation strategy reaches a neutral balance of –0.00 kg/year, satisfying the legal test of no adverse effect on the Ramsar site.

Faraday Road, Kirkby Stephen - Achieving Nutrient Neutrality

Fri, 21 Nov 2025 03:30:07 GMT

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

Proposed Development & SuDS Strategy

Nutrient Budget Calculations

Ground Investigation & Design Confidence

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.

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.

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.

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.

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

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Kirby Stephen

2025

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.

Pound Road, Broadway - Achieving Phosphorus Neutrality

Fri, 21 Nov 2025 03:09:14 GMT

Why Nutrient Neutrality Is Required

Natural England issued guidance stating that additional phosphorus from new development may adversely affect the Somerset Levels & Moors Ramsar Site, which is currently in an “unfavourable condition” due to excessive nutrient levels.

As a result, Local Planning Authorities must ensure that any proposed residential development does not increase phosphorus loading without mitigation.

Existing Site Conditions

Proposed Development & SuDS Strategy

Nutrient Budget Calculations

Final Nutrient Budget

Conclusion

The report states unequivocally:

“The applicant shall achieve Nutrient Neutrality through the proposals and therefore nutrient arisings should not prevent planning approval being granted.”

Through the integration of a robust SuDS treatment train and the favourable baseline export from lowland grazing, the Pound Road site achieves a net reduction of 0.64 kg TP/year, requiring no offsite mitigation.

The development includes:

45 dwellings with foul connections to Broadway WRC
Surface water managed entirely on-site via a SuDS treatment train including ponds and basins

SuDS Performance

The report uses CIRIA C808 removal efficiency values. A pond treatment train provides:

39% particulate P removal
23% dissolved P removal
62% total phosphorus removal efficiency

The report confirms that the SuDS are designed to manage both PP and DP, preventing bioavailable phosphorus from entering the receiving environment.

The report shows:

Former land use: Lowland grazing (3.129 ha)
Annual phosphorus export: –3.82 kg TP/year
Soil drainage type: Impeded
Annual rainfall: 900–950 mm

The baseline therefore generates a net phosphorus export, a favourable position for nutrient budgeting.

The report’s Stage 4 summary concludes:

Final phosphorus load (Pre-LURA): –0.64 kg TP/year
Final phosphorus load (Post-LURA): –0.64 kg TP/year

This is a net reduction, meaning the site will export less phosphorus after development than it does today.

Stage 1 – Wastewater Arisings

The annual foul-water phosphorus contribution is:

+2.04 kg TP/year (Pre-LURA & Post-LURA)

CD4.14 - 10829 TN01 RV4 - Nutri…

Stage 2 – Existing Land Use

–3.82 kg TP/year (export from lowland grazing)

CD4.14 - 10829 TN01 RV4 - Nutri…

Stage 3 – Proposed Land Use

Residential Urban: 1.568 ha
Green Space: 1.561 ha
+2.93 kg TP/year export

SuDS Reduction

–1.80 kg TP/year removed by SuDS

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Somerset

2025

Enviren successfully demonstrated that a residential scheme of 45 dwellings at Pound Road, Broadway could be delivered without increasing phosphorus loads to the sensitive Somerset Levels & Moors. Despite initial expectations that new foul and surface water flows would increase nutrient discharge, the project team identified that:

The existing low-intensity grazing land already exported phosphorus.
The proposed development footprint was tightly balanced between residential and greenspace land uses.
A carefully selected SuDS treatment train, achieving 62% phosphorus removal, would offset the small increases in urban runoff.

The final nutrient budget shows a net improvement in phosphorus loading relative to the existing baseline, ensuring full compliance with Natural England’s nutrient neutrality requirements and removing the need for costly offsite land or constructed wetland mitigation.

Mudford, Yeovil - Achieving Phosphorus Neutrality

Wed, 19 Nov 2025 02:03:19 GMT

Updated Wastewater Loads

Enviren’s Stage 1 wastewater calculations show the following reductions due to AMP7 and future permit tightening:

45.73 kgP/year (Current)
13.49 kgP/year (Post-2025)
5.72 kgP/year (Post-2030)

This is a dramatic reduction compared with earlier assumptions.

Land-Use Change Calculations

Final Nutrient Budget

Why Enviren Achieves Neutrality (Key Factors)

Competitor’ Findings: Requirement for Large-Scale Offsite Mitigation

Competitor’ Proposed Mitigation Requirements

The competitor identifies offsite mitigation options due to the scale of the +50.99 kgP/year load:

Option 1 – Fallowing

72 ha of lowland grazing, or
57 ha of cereal fields
required to offset the load.

Option 2 – Constructed Wetlands

A 4.25 ha traditional wetland, or
1.1 ha of floating wetland
required to offset the phosphorus load.

The competitor therefore concludes that significant offsite land or complex engineered wetlands are necessary—whereas Enviren determines that no mitigation is needed at all.

Enviren calculates the following final phosphorus budgets:

Existing cereal cropping exports –21.16 kgP/year
Proposed land-use mix (residential, orchard, greenspace, water + SuDS) results in +5.21 kgP/year

Competitor’ assessment arrives at dramatically different conclusions.

Total Phosphorus Budget

Competitor calculates a positive phosphorus budget of +50.99 kgP/year, requiring mitigation:

“Mitigation measures will be required to offset additional 50.99 kgP/year discharged from the site…”

This figure is significantly higher than Enviren’s positive current-permit budget of +35.73 kgP/year—and far higher than the mitigation-free negative budgets under 2025/2030 limits.

AMP7 and Post-2030 discharge limits applied
– Competitor pre-dated these values.
62% SuDS phosphorus-removal efficiency applied to surface water runoff
– Based on CIRIA C808
A detailed SuDS treatment train managing both particulate and dissolved phosphorus – Includes sediment capture, wet ponds, and treatment media targeting phosphorus
Large areas of on-site greenspace (13.144 ha) with low nutrient export rates.
Cereal land baseline creates a favourable pre-development nutrient position.

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Yeovil

2025

This case study highlights how Enviren’s approach — grounded in updated data, improved SuDS design, and revised permit assumptions—achieves significant phosphorus reductions relative to the Competitor analysis. This case study is based on a 252 dwelling scheme in Mudford, Yeovil, Somerset.

Key Comparative Insight: The Reduction Achieved by Enviren

Conclusion

Enviren’s 2025 Nutrient Neutrality Assessment transformed the development prospects for the Mudford Road site. Earlier assessments had suggested that the site would generate over 50 kg of additional phosphorus per year, requiring up to 72 hectares of offsite land or extensive artificial wetlands.

Using updated wastewater permit limits, improved SuDS design, and refined nutrient modelling, Enviren demonstrated that the scheme can achieve full phosphorus neutrality on site, reducing the phosphorus impact to –10.24 kgP/year under post-2030 conditions.

This represents an effective reduction of more than 60 kgP/year compared with the previous assessment—eliminating the need for costly offsite land purchase or wetland construction and significantly accelerating deliverability.

Enviren vs. Competitor: Final TP Loads

Critically, Enviren confirms:

“Development will be Phosphorus neutral – no mitigation will be required.”

This means the site is self-mitigating under foreseeable permit conditions.

Total effective reduction achieved by Enviren (Competitor → Post-2030):

≈ 61.23 kgP/year reduction

This reduction is achieved through:

incorporating newer WRC permit limits
enhanced SuDS phosphorus reductions
refined land-use modelling
updated rainfall and catchment data
more accurate cereal-land baselines

Horton Cross, Ilminster - Flood Risk Assessment & Drainage Strategy

Wed, 19 Nov 2025 01:11:45 GMT

Project Overview

The proposal comprises:

Construction of a new warehouse facility
Associated infrastructure, including parking and drainage
Works on land currently used for general storage (no increase in vulnerability)

The report supports the planning submission by assessing flood risk, setting out drainage measures, and ensuring compliance with NPPF, Somerset Council policy, and wider technical standards.

Site Location & Existing Conditions

Sources of Flood Risk

Drainage Strategy

Foul Water Strategy

Flood Mitigation Measures

Key Measures from the FRADS include:

Slab levels raised ≥300 mm to mitigate groundwater ingress
All below-ground drainage components wrapped and sealed
Attenuation basin and pond lined with impermeable membrane
Freeboard and flood confidence scoring ensuring robust design
Drainage construction sequencing to avoid temporary increases in flood risk during works

Enviren evaluated six sources of flooding, with results summarised below.

Fluvial Flooding

The site lies largely within Flood Zone 1 (low risk).
A small eastern segment abuts Flood Zone 3 due to proximity to the River Isle, but all built development avoids this area.

Surface Water Flooding (Pluvial)

Minor surface water pooling is shown in mapping.
Mitigated through re-profiling and introduction of a pond and detention basin.

Groundwater Flooding

SFRA mapping indicates high groundwater risk.
Addressed through:
Raising slab levels by 300 mm
Sealing below-ground infrastructure
Lining attenuation features with impermeable membranes

Sewer Flooding

Historic sewer issues exist within the wider postcode area, but none directly affecting the site.
Non-return valves may be installed if Wessex Water identifies network constraints.

Reservoir / Artificial Waterbody Flooding

Site is mapped at medium risk from reservoirs, but this is very unlikely to affect the site due to controlled and maintained structures.

Location & Setting

Situated at Horton Cross, accessed via Station Road (southern access).

Ground Conditions

Underlain by Charmouth Formation clay/mudstone, which has impeded drainage characteristics.

Catchment & Topography

The eastern part of the site is adjacent to the River Isle.

Foul flows discharged to the public foul sewer along Station Road.
Conveyed via new pumping station → break chamber → gravity connection.

Surface Water Management

The drainage design is centred on:

Sustainable Drainage Systems (SuDS)

A detailed SuDS assessment identifies suitable measures, including:

Porous paving
Swales
Detention basin
Pond

Hydraulic Performance

FEH rainfall data used to reflect modern rainfall patterns.

Final Discharge

Surface water discharges to the existing pipe serving the car park, which outlets into the River Isle.

Betterment Over Existing Rates

Proposed discharge rates remain below QBAR for all storm events.

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Powrmatic

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Ilminster

2025

Enviren’s FRADS for the Powrmatic facility at Horton Cross demonstrates a robust, well-engineered approach to flood risk and drainage.

Through strategic use of SuDS, careful site design, and targeted mitigation, the assessment shows that the new warehouse can be safely developed despite challenges from groundwater and proximity to the River Isle. The final strategy delivers environmental betterment, regulatory compliance, and long-term resilience.

Water Quality Assessment

Conclusion of the FRADS

The assessment concludes:

The development will not be at significant flood risk for its design life.
Proposed SuDS and foul water strategies appropriately control runoff and protect water quality.
Flood risk and water quality should not prevent planning approval.

Using the CIRIA C753 Simple Index Approach, the FRADS confirms:

The SuDS treatment train provides adequate pollutant mitigation,
Safeguarding downstream waterbodies including the River Isle.

Earle Street, Yeovil - Flood Risk Assessment & Drainage Strategy

Wed, 19 Nov 2025 01:10:19 GMT

Project Overview

The FRADS confirms:

Development type: Block of flats
Location: Construction Site, Earle Street, Yeovil, BA20 1JW
Purpose: To demonstrate that the development can be safely designed in respect of flooding and that runoff can be managed effectively.
Objective: Mitigate all identified flood risks and provide a compliant drainage strategy under NPPF requirements.

Assessment of Flood Sources

Overland Flow & Culvert Capacity Analysis

Impact of Development on Catchment Flood Risk

Drainage Strategy

Overall Conclusion

The FRADS concludes:

The development is not at significant flood risk for its design life.
Surface water can be safely managed using the proposed drainage strategy.
Downstream flooding and water quality impacts are improved, not worsened, by the development.

A major element of the FRADS is the hydraulic assessment of upstream catchment flows and the capacity of the culverted system.

Key Findings

CCTV survey (Appendix I) identified sedimentation and deposits, so a 20% reduction in hydraulic capacity was applied for conservatism.
Even with this reduction:
Northern catchment flow: 3136.1 l/s
Eastern catchment flow: 154.6 l/s
Culvert beneath site: 1449.2 l/s
Culvert under Wyndham Street: 4187.4 l/s
Free capacity available: 2253.1 l/s
The off-site combined sewer system contributes to historical flooding elsewhere in Yeovil, but this is independent of the development and not attributable to flows from the site.
The hydraulic assessment confirms that surface water flooding need not be considered further because the culverted system is sufficiently oversized.

The FRADS evaluates all flood risk types.

Fluvial Flooding

The River Yeo is ~330 m south of the site.
Assessed risk: Low.

Surface Water Flooding (Pluvial)

Surface water flooding will not affect the development based on modelling and capacity checks.

Sewer Flooding

Sewer flooding does not affect the development site.

Reservoir, Canals & Tidal Flooding

All assessed as no risk or low risk.

Overall: All sources of flooding to the proposed development are Low or None.

The drainage design emphasises:

Surface Water Management

Removal of surface water discharge from combined sewers → reduced CSO discharges into the River Yeo.

Water Quality Protection

Treatment train includes permeable paving and a bypass separator.
Assessed using the CIRIA C753 Simple Index Approach.

Overall Performance

Significant betterment in discharge rates over the existing situation.

The development introduces only a small increase in impermeable area.
The strategy incorporates appropriate mitigation, ensuring no worsening of flood risk downstream.

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Yeovil

2024

According to a document from 2021–2024, the Flood Risk Assessment and Drainage Strategy (FRADS) was prepared to support the redevelopment of a block of flats at a site off Earle Street, Yeovil, Somerset.

The report evaluates fluvial, surface water, sewer, and overland flow risks and provides a comprehensive drainage strategy to ensure the scheme will not increase flood risk locally or downstream.

Corinthian Park, Cheltenham - Flood Risk & Surface Water Strategy

Wed, 19 Nov 2025 00:44:58 GMT

Project Overview

Enviren prepared a Flood Risk Assessment (FRA) for Revival Developers Limited to support a planning application at Corinthian Park, Cheltenham. The scheme comprises:

Up to 60 dwellings, and
Up to 550 m² of flexible commercial space, together with associated infrastructure and works.

The FRA is explicitly prepared in line with the NPPF, Planning Practice Guidance and local policy (Cheltenham Borough Council SFRA, GCC LFRA etc.).

Site Location & Existing Conditions

Sources of Flood Risk

Catchment & Hydraulic Analysis

Mitigation Strategy

Overall Flood Risk Outcome

The conclusion section summarises post-mitigation risk as follows:

Fluvial: Very low – site is in Flood Zone 1 and not influenced significantly by main rivers.
Pluvial: Low–medium risk without mitigation, reduced to acceptable / low risk by ditch widening and flow management.

The FRA states:

“In compliance with the requirements of the National Planning Policy Framework, and subject to the mitigation measures proposed, the development could proceed without being subject to significant flood risk. Additionally the development will not increase flood risk to the wider catchment area owing to suitable management of surface water passing through the land parcel.”

And:

“Providing the flood mitigation strategies outlined in this document are implemented, flood risk should not prevent approval being granted to this development.”

The FRA considers fluvial and pluvial risk using EA, local authority and SCALGO mapping.

Fluvial / Tidal (River & Sea)

Strategic Flood Risk Assessment mapping shows the development parcel lies entirely in Flood Zone 1, i.e. very low risk of river or sea flooding.

Pluvial (Surface Water) – Primary Risk

EA surface water maps and detailed SCALGO modelling identify the site as being at risk principally from pluvial flooding, with flow paths crossing the land towards the west.

The FRA therefore focuses on:

Overland flow routing through the site,
Capacity of the existing and proposed ditch along the western boundary, and
Ensuring the development does not increase flood risk downstream.

Location

The site is:

On the western edge of Cheltenham,
Located between the A40 and North Road West,
Approximately 4.41 km west of Cheltenham town centre and 7.35 km east of Gloucester city centre.
The existing site is greenspace (grassland with some stockpiles), about 1.650 ha in area, bounded by roads to north and south, a commercial estate to the east and gardens/dwellings to the west.

Outline Hydrology

Topographical analysis (SCALGO) shows:

Runoff from the majority of the site flows west into a minor watercourse off Badgeworth Road,
That watercourse then flows north and west, ultimately discharging to the River Severn via Hatherley Brook.

Ground Conditions

The site is underlain by the Charmouth Mudstone Formation (mudstones and shales with limestone bands).

HR Wallingford’s greenfield runoff tool indicates:

SPR = 0.370 (SOIL type 3) → slightly impermeable soils.

Western Ditch Regrading & Capacity

A key mitigation measure is to widen and regrade the base of the existing ditch on/adjacent to the western boundary to provide:

Sufficient capacity for pluvial flows from the catchment.
Level-for-level floodplain compensation relative to current RoFSW-identified storage.
Existing ditch capacity calculations.
Proposed ditch capacity after regrading, showing an increase in flow capacity from ~0.32 m³/s to ~0.76–0.85 m³/s for the 1 in 100 year + 40% CC event (derived from cross-sectional areas in the Northern Ditch Sections drawing).

Managing On-Site and Downstream Risk

The FRA concludes that:

The widened ditch provides sufficient storage and conveyance to protect both the development and downstream receptors from pluvial flooding.
The drainage strategy ensures no increase in flood risk to the wider catchment by managing surface water through the land parcel in a controlled way.

The report includes:

Catchment analysis and a delineated flow-path catchment contributing to the western ditch,
SCALGO wider topographic mapping to understand regional flow routes,
A hydrograph-based model of flows to the culvert/watercourse system.

Model outputs (Flow+ / Innovyze) test a range of storm durations (15–1440 minutes) for the 1 in 100 year + 40% climate change event, with mass balance close to 100%, and show the culvert and downstream system can convey the design flows when the ditch is appropriately sized.

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Cheltenham

2025

For Corinthian Park, Cheltenham, Enviren’s FRA shows that a mixed residential–commercial scheme (up to 60 dwellings and 550 m² flexible space) can be safely delivered on a site that is nominally at risk from surface water flooding.

By carefully analysing the wider catchment, modelling flows through the western ditch and culvert system, and then re-profiling that ditch to increase capacity and storage, the design:

Keeps the new development outside significant pluvial hazard,
Maintains or betters pre-development flow conditions, and
Ensures no increased flood risk to neighbours or downstream receptors.

The FRA provides a clear, policy-compliant technical justification for granting planning permission, contingent on the specified mitigation being implemented.

Station Road, Crewkerne - Comprehensive Flood Risk Assessment & Drainage Strategy

Wed, 19 Nov 2025 00:04:49 GMT

Site Overview

Site characteristics

Location: West of Station Road, Crewkerne, Somerset
Site area: 16.532 ha
Existing land use: Agricultural (less vulnerable)
Proposed use: Residential (more vulnerable)

Topography & Hydrology

Runoff flows north toward the River Parrett

A watercourse runs along the west of the site, eventually discharging to the River Parrett

Flood Zone Status

The entire site lies within Flood Zone 1 (lowest fluvial/thalassic risk)

Sources of Flood Risk

Surface Water Drainage Strategy

Foul Water Strategy

Flood Risk Mitigation Measures

Summary of Post-Mitigation Flood Risk

Final Conclusion

According to the FRADS:

“Providing the flood mitigation strategies outlined in this document are implemented, flood risk should not prevent approval being granted to this development.”

The site is demonstrably safe from all key flood sources, and the drainage strategy—primarily infiltration—ensures no increase in flood risk to the wider catchment.

Table 8.1 shows:

Core principles

The drainage strategy adheres to:

The SuDS hierarchy
Somerset Council requirements
NPPF and Planning Practice Guidance

Primary discharge option — infiltration

The report recommends infiltration-based drainage where viable.

Evidence for infiltration viability

A separate supported soakaway investigation confirms:

No groundwater encountered in any trial pits
Limestone and clay strata across the site
Infiltration rates were successfully established in several pits.

Fallback strategy

If further sitewide infiltration testing finds areas unsuitable or if groundwater rises:

An alternative drainage layout has already been prepared

This ensures the scheme can manage runoff under all expected conditions.

The FRADS assesses all flooding mechanisms as required by the National Planning Policy Framework (NPPF).

Fluvial flooding

Very low risk — site is entirely Flood Zone 1

Surface water (pluvial)

Very low risk across the developable area

Groundwater flooding

Low risk, but the report identifies the need for ongoing groundwater monitoring

Sewer flooding

Very low risk

Reservoir flooding

Very low risk, reservoir flooding does not reach the site

The FRADS prescribes the following:

Groundwater monitoring

Required to track seasonal variations and identify potential rising trends

SuDS features

The strategy incorporates:

Swales
Attenuation basins
Porous surfaces
Rainwater harvesting
Greenfield runoff compliance

All surface water discharge is constrained to greenfield runoff rates and volumes.

Catchment impact

Runoff will be managed entirely on-site through infiltration, ensuring no downstream flood risk.

The FRADS confirms:

Foul water will discharge to the main foul sewer along Station Road

There is no reference to requiring on-site treatment or alternative foul measures in this document.

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GTH

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Crewkerne

2025

Enviren prepared a comprehensive Flood Risk Assessment and Drainage Strategy in support of a planning application for 325 dwellings and associated infrastructure on land west of Station Road, Crewkerne.

The assessment demonstrates that, with appropriate mitigation, the scheme is safe from flooding and will not increase flood risk elsewhere.

The Planning and Infrastructure Bill - The Legislation We Needed

Mon, 17 Mar 2025 02:03:19 GMT

Nutrient Neutrality - An onsite perspective.

Most will agree that a levy system is a practical and logical approach to delivering nutrient neutrality which shall allow developers to build without facing the roadblock of demonstrating nutrient neutrality themselves. However, introducing such legislation in its current form at this current time is potentially damaging if it does not leave scope for onsite assessments and the input of private credit suppliers.

The legislation smacks of a shadow government that has been waiting in the wings far too long and has watched the disastrous handling on nutrient neutrality by the previous government. The Conservative government made ill-considered attempts to scrap nutrient neutrality entirely, posturing over several months which destroyed investor confidence in the market. This is the critical reason that NN effected areas have seen such a low throughput of quality, reasonably priced nutrient credits. Where investor confidence has withstood we are now seeing a good supply of reasonably priced credits which developers can readily afford with reasonable payment terms (see Somerset).

Implementing a levy system at this stage, populated by Natural England or another Delivery Body, simply creates another wave of uncertainty for the private market spanning potentially 18 months until the bill gets royal assent. This will result in another significant period without nutrient credits being available to developers thus resulting in a self-fulfilling prophecy of the private market being unable to meet supply. This prophecy also leads to a skill shortage in the sector as organisations are unwilling to commit resources or hire new staff in such a volatile industry.

Even with the instability, the private sector has managed to deliver significant quantums of mitigation and produce real innovation in the sector. Natural England have not been able to deliver significant quantums of mitigation, particularly in relation to phosphorus, and look posed to pursue spatially intensive arable land reversion schemes in order to generate credits. There is no certainty, at this stage, that the cost of mitigating through the levy will be any less than purchasing mitigation through a private third party, with nitrogen credits sold by Natural England costing more in the Poole Harbour than private credit suppliers elsewhere in the country.

Onsite nutrient neutrality has been a tiring and overwhelming process where minute details are fought tooth and nail with the regulator. However, only through onsite assessments can the Delivery Body be sure that they are providing the correct amount of mitigation for the catchment without over committing resources. We have shaved 20kg/year of phosphorus off a developer's budget on a single site through simple, un-invasive controls that should be considered best practice. We have managed to reduce the liability of a single dwelling development down from 3.0kg/year to just over 0.10kg/year (yes, 3.0kg/year for a single house!). A large proportion of developments simply does not need mitigation, providing the calculations are performed correctly.

If onsite assessments are not continued then there will be no incentive to reduce nutrient budgets through measures such as specifying tailored SuDS treatment trains or utilising top of the range Package Treatment Plants for off-mains proposals. If a developers final nutrient budget can be mitigated at a lower cost than the levy then developers will inevitably seek their own solution.

When setting a levy one needs to protect our rural communities whilst permitting strategic developments at cost and pace. If a flat levy is implemented then larger developers will likely lobby for a price decrease, where proposals are typically closer to larger settlements with a higher performing Wastewater Treatment Works. To remedy these conflicting interests a banded system must be implemented, with scope for onsite assessments, as outlined in the diagram in this post. This will ensure that development that has no impact shall not pay, that developments with a lower cost per roof pay the least and those with a higher budget pay more, whilst ensuring that the prices in Tier 3 are not preventatively high.

The outstanding supply of private credits/LPA generated credits must be factored into the mitigation stock of the Delivery Plan outlined by the Delivery Body and contribute to the Nature Restoration Fund to kickstart mitigation delivery. For the levy to be a success it needs to welcome private input and supply, both to provide the necessary quantum of mitigation for the strategic mitigation but also for a developer to explore all options available to them.

Announcing the Greenshank and Enviren Partnership

Fri, 07 Mar 2025 09:42:33 GMT

Press Release: 07/03/24

We are very pleased to announce our new partnership with Greenshank Environmental.

Over the past year, we have been collaborating on many projects, culminating in Greenshank taking a stake in Enviren this March. Zak Simmonds , Enviren Owner said 'Our partnership will amplify the work we have been doing in onsite nutrient mitigation, drainage design and flood risk. Our market-leading services will be extended, adding Greenshank's expertise in offsite nutrient mitigation and biodiversity net gain.'

Dr. Gabriel Connor Streich, CEO of Greenshank, has been at the forefront of producing guidance on nutrient neutrality and he continues to work closely with Natural England to standardise novel approaches to offsite nutrient mitigation. Gabriel commented 'By combining Enviren’s ability to achieve full neutrality in over 90% of new housing developments, with Greenshank’s market-leading expertise in offsite nutrient mitigation, we can provide the most cost-effective solutions to nutrient neutrality anywhere in the country. This is going to be a game-changer.'

If you have any questions or would like to explore working together please email on enquiries@enviren.co.uk

Zero-Discharge Willow Beds - Notes from Denmark

Fri, 24 Nov 2023 09:53:26 GMT

Over the last year we have been investigating the potential of zero-discharge willow bed systems to enable developers to overcome the nutrient neutrality issue. The concept of zero-discharge willow bed systems is that the beds use evapotranspiration to remove all the liquid wastewater generated by the new development, thus achieve nutrient neutrality. We have been working hard on this to bring the use of this technology into sewered catchments such that a dry overflow pipe would mean that developers can connect to the main sewer (in line with the Buildings Regulations, EA general binding rules and the NPPF) whilst not generating any nutrients.

We headed over to Denmark in September to meet international expert and pioneer Peder Gregersen to discuss his successes and see the systems in persons and we were amazed to see them not only surviving but thriving, some of them being in use for decades. Peder also enlightened us on the carbon reduction benefits of the willow beds which is another benefit to their incorporation. We have now refined the design process and we are pleased to announce that we will be working in cooperation with Peder on new projects across England and Wales to introduce this incredible technology. The part of this that makes us most proud is that we will have the opportunity to carry Peder's legacy on.

The willow beds needs to be carefully designed, paying close attention to local climatic conditions and topographical information. Key considerations include:

Hours of sunlight
Wind travel
Altitude
Coordinates
Temperature
Humidity
Local rainfall rates
Soil porosity
Neighbouring trees and structures

We really look to forward to pushing this technology forwards and using it on larger, more expansive developments as a cost effective and sustainable alternative to credits.

Nutrient Neutrality - The Wider Impact

Sun, 13 Aug 2023 09:43:34 GMT

The quality of our rivers and water resources has become a key political issue amid wider environmental concerns on how we as a species interact with the wider environment and our planet.

It is often tempting to take the path of least resistance, to continue on an established route with little consideration to the wider consequences. But, after some time, that ignorance, that neglect begins to creep up on you and can lead to disaster. The UK is finding itself in the middle of such a disaster. In 2022, a House of Commons Committee report found that only 14% of UK rivers had a "good" ecological status. Of the near 1,500 rivers in the UK, only 2 rivers are designated as "Bathing waters" and both are currently too polluted to use. Combined Sewer Overflows (CSOs) are periodically discharging untreated sewage into our watercourses and much of the infrastructure is outdated and not appropriate for this day and age.

We are all largely aware of these issues, especially industry leaders and politicians in office, yet as a society we largely respond in lukewarm vexation. Owing to nutrient neutrality, water quality has suddenly become central focus for many local authorities, developers, planners, water authorities and consultants, who have been forced to truly consider the impact of proposed development.

As a result of nutrient neutrality there are wider social and environmental benefits. Through the issue of CIRIA C808 an accompanying benchmark has been established to the best practice SuDS design principles outlined in CIRIA C753, with a focus on how phosphorus is treated by SuDS, something in the past that barely received a mention in the SuDS manual. What's more the dust has been blown off CIRIA C609 for nitrogen removal efficiencies. This has resulted in SuDS schemes that willingly incorporate best practice, embracing source control elements, considering interception and introducing intermediary conveyance based SuDS, rather than simple pipe-to-pond systems. Also there is appetite for the detailed design of treatment components to maximise biological precipitation and denitrification. This aligns well with the enactment of Schedule 3 of the Flood and Water Management Act 2010, which shall hopefully result in good, well considered SuDS being incorporated on all new development, securing true compliance with the classic 4 pillars; water quality , water quantity , amenity and biodiversity .

The consideration of nutrient neutrality has lead to developers actively seeking to remove surface water from the combined sewer network, something in the past which would largely not have been given a second thought without interventions from the water authority and updated government guidance. This would maximise the benefits achieved from developing brownfield sites.

Exciting solutions, which were previously not economically viable, are now becoming key considerations in drainage design strategies, such as grey-water recycling and rainwater harvesting, both to minimise water output. A more holistic approach to water is being adopted, not only at a catchment scale but at a site scale. Similarly, water efficiency has become a key focus and the construction sector is turning to existing housing stock to remedy extant inefficiencies.

In addition Sustainable Drainage Systems (SuDS), once something only considered for surface water, are now being adopted to treat foul water through secondary and tertiary cleansing, biofiltration and evapotranspiration, setting a new precedent on how we use and handle our waste. The inception of New Appointments and Variations (NAVs) allows developers to accelerate improvements to the water network and implement the highest levels of technology onsite.

There is also now financial incentive to replace polluting drainage infrastructure. The Environment Agency is cut back to the bone and cannot realistically enforce the need to change over septic tanks discharging to watercourses; however, owing to nutrient neutrality operators have the means and the drive to replace such systems, providing wider benefits to rivers and the environment, beyond just nutrients.

Finally, private credit marketplaces are coming forward, driven by incredible ambition and innovation, which are promising the rewilding and improvement of our water network through measures such as riparian buffer strips, wetland designs and the reestablishment of lost drainage networks.

What more innovations are to come from such a divisive and decisive issue? The adoption of evapotranspirative green roofs within catchments with combined sewers? A more cyclical approach to chemical dosing and the harvesting of vivianite for reuse? The use of algae based systems and low DO treatment to provide enhanced nutrient removal? The list of potential benefits is mind boggling and we appear to be only scratching the surface.

Therefore, the key question we need to ask ourselves is: although temporarily this is painful for many, will it be worth it?

Nutrient Neutrality = Sorted

Fri, 03 Mar 2023 11:31:19 GMT

Enviren has been producing nutrient neutrality assessments since very early on in Nutrient Neutrality crisis and we believe we are the best at what we do, offering the most comprehensive range of practical solutions at a reasonable price with the client very much at the forefront of our minds. We offer a service which looks to protect the clients assets following our hierarchy of mitigation:

Look at existing site arisings and demonstrate nutrient neutrality without any mitigation measures.
Introduce site specific, engineered controls to achieve nutrient neutrality.
Look at surrounding land holdings to deliver mitigation.
Pursue a credit based system to provide the necessary offsetting.

At this point we believe that we can achieve nutrient neutrality for the vast majority of developments (over 90%), with our service we outline how we plan to achieve nutrient neutrality prior to completing the report to ensure that the client is absolutely satisfied with the proposals we bring forward. Through our mitigation methods clients have saved tens of thousands of pounds and their planning applications have been expedited. Our mitigation strategies include:

Discharge of wastewater to ground through a drainage field.
Discharge of wastewater to ground through a drainage mound.
Replacing septic tanks with Package Treatment Plants.
Replacing existing Package Treatment Plants with higher performing Package Treatment Plants.
Undertaking plume spread analysis.
Removing surface water from the combined/foul sewer network.
Introducing water efficiency measures.
Installing greywater recycling systems.
Introducing rainwater harvesting systems.
Utilising zero-discharge willow beds.
Designing Sustainable Drainage Systems (SuDS) specifically for the removal of nutrients.
Analysing localised potential for denitrification and biological precipitation
Introducing filter beds to provide secondary and tertiary cleansing.
Utilising interception measures to reduce nutrient loads.
The detailed design of wetlands to reduce nutrient loads.
The design of riparian buffer strips to reduce nutrient loads.
Connecting existing development to the sewer network to provide the requirement mitigation.
Converting surrounding land to a less phosphorus intensive land use.

Do not delay, get in contact with us today to see how we can assist and get your planning application back on track.

Enviren Successful Flood Risk Assessment

Mon, 25 Apr 2022 11:36:03 GMT

Enviren has expertly designed the surface water drainage system and successfully argued that surface water flooding does not pose a concern for a proposed development in Standerwick in Mendip District, Somerset.

The scheme was for five caravan pitches which faced strong local competition. Enviren successfully argued that the project was not at risk of surface water flooding and provided the client with a successful alternative to soakaway drainage, where infiltration rates did not support their use. The proposals utilised flow control devices and sub surface storage to make a piped connection to an existing culverted watercourse, saving the client months on their planning application as well as money.

Can we help progress your proposals with a tailored flood risk assessment? Please get in touch with us to see how we can assist.

Drainage Design - Efficient, Cost Effective and Sustainable

Mon, 25 Apr 2022 11:32:09 GMT

Enviren really does strive for perfection when it comes to drainage design. With our detailed drainage designs we are looking for the most efficient solution possible with three things in mind:

Our Clients - Our clients are always our priority, we aim to save our clients as much money as possible and the best way of achieving this also ties into our second objective and this is minimising waste! So often drainage systems are designed with overpriced, over-specified concrete systems, which are inefficient and harmful to the environment and we have saved past client tens of thousands of pounds through well-considered design. We look to provide intricately designed drainage networks to suit the development size for the lowest possible price and for a more than competitive design fee.
Sustainability - We love our planet at Enviren and we strive to achieve carbon reductions within our schemes as far as possible, whether this be subbing in more eco friendly building materials or incorporating sustainable drainage systems in tactical locations to provide attenuation and water cleansing. When it comes to SuDS (Sustainable Drainage Systems) we are really leading the way in the construction industry, we know them inside and out and we design such systems with due regard to not just water quantity, but water quality, amenity and biodiversity. We will work with your landscaper to make sure the right plants are installed, we can provide maintenance regimes and we can make sure the system is properly wrapped, lined, designed and constructed.
Water Quality - We also promote achieving high water quality with a development's surface water discharge and we are ahead of the game on many issues, including Nutrient Neutrality. We can provide calculations of varying complexity to suit your requirements, from the Simple Index Approach to Vt calculations, all the way up to First Order Plug Flow Reactor Kinetic modelling for wetland design.

We strive to achieve a design solution which not only saves money, but leads to a fast planning approval and achieves the lowest environmental impact possible reaching for a net gain in biodiversity where possible. Get in touch with us today and see how we can help you.

Enviren Forms

Sun, 05 Dec 2021 10:32:36 GMT

Enviren has formed to provide much needed drainage design solutions and water quality consultation. Principally operating in Somerset to assist with the current Ecological Emergency due to Phosphorus, Enviren can also offer precise Engineering designs and advice for surface and foul water drainage systems to ensure these are operating as efficiently as possible and are ready for adoption by the Water Authority.

Enviren can provide services across the UK to clients of varying size, from one home to large scale developments. Please, get in touch and see how we can help you today.

Enviren - Planning Consultants

Station Road, Crewkerne - Achieving Phosphorus Nutrient Neutrality

Site & Development Overview

Baseline Conditions

Nutrient Budget Calculation

Off-Site Mitigation Through P-Credit Acquisition

Conclusion of the NNAMS

CLIENT

LOCATION

PROJECT DETAILS

Similar Project?

COMPLETED

OFFICE

Why This Scheme Is a Strong Example

Faraday Road, Kirkby Stephen - Achieving Nutrient Neutrality

Environmental & Regulatory Context

Existing Site Conditions ﻿

Proposed Development & SuDS Strategy

Nutrient Budget Calculations

Ground Investigation & Design Confidence

Conclusion ﻿

CLIENT

LOCATION

PROJECT DETAILS

Similar Project?

COMPLETED

OFFICE

Pound Road, Broadway - Achieving Phosphorus Neutrality

Why Nutrient Neutrality Is Required

Existing Site Conditions

Proposed Development & SuDS Strategy

Nutrient Budget Calculations

Final Nutrient Budget

Conclusion

CLIENT

LOCATION

PROJECT DETAILS

Similar Project?

COMPLETED

OFFICE

Mudford, Yeovil - Achieving Phosphorus Neutrality

Updated Wastewater Loads

Land-Use Change Calculations

Final Nutrient Budget

Why Enviren Achieves Neutrality (Key Factors)

Competitor’ Findings: Requirement for Large-Scale Offsite Mitigation

Competitor’ Proposed Mitigation Requirements

CLIENT

LOCATION

PROJECT DETAILS

Similar Project?

COMPLETED

OFFICE

Key Comparative Insight: The Reduction Achieved by Enviren

Conclusion

Horton Cross, Ilminster - Flood Risk Assessment & Drainage Strategy

Project Overview

Site Location & Existing Conditions

Sources of Flood Risk

Drainage Strategy

Foul Water Strategy

Flood Mitigation Measures

CLIENT

LOCATION

PROJECT DETAILS

Similar Project?

COMPLETED

OFFICE

Water Quality Assessment

Conclusion of the FRADS

Earle Street, Yeovil - Flood Risk Assessment & Drainage Strategy

Project Overview

Assessment of Flood Sources

Overland Flow & Culvert Capacity Analysis

Impact of Development on Catchment Flood Risk

Drainage Strategy

Overall Conclusion

CLIENT

LOCATION

PROJECT DETAILS

Existing Site Conditions

Conclusion

Nutrient Neutrality - An onsite perspective.