Enabling sustainable phased earthworks and regulatory agreement for a major residential development in West Sussex

Overview

Omnia Consulting supported our client with a bespoke Materials Management Plan (MMP) on a complex site in Ford, West Sussex.

Ford Airfield is a major phased residential development in Ford, West Sussex, where Vistry South East is bringing forward up to 1,500 dwellings across multiple reserved matters phases. Omnia has supported the project from the pre-purchase stage, acting as geo-environmental consultant and helping the client navigate site investigation, historic data review, hotspot contamination issues and material reuse planning.

A central requirement was to find a practical and robust way to reuse site-won materials across a long-term, multi-phase development while remaining aligned with the principles of the CL:AIRE Definition of Waste: Development Industry Code of Practice. The site presented an important opportunity to avoid unnecessary disposal, reduce import requirements, and support a more sustainable earthworks strategy.

Scope of Works

The development is being delivered through ten reserved matters phases. At the time the strategy was developed, not all phases had full ground investigation coverage, approved remediation strategies or fixed levels information. This created a challenge for a conventional site-wide MMP submission because the standard lines of evidence for protection of human health and the environment, suitability for use, certainty of use and quantity of material could not yet be fully closed out for every phase.

The client also needed flexibility to move clean natural soils between phases and to reuse impacted soils within active phases. Without a bespoke approach, surplus material from early phases may have required off-site disposal, while later phases with material shortfalls may have needed imported soils. The scale of the opportunity was significant: upwards of 65,000 m³ of topsoil and upwards of 285,000 m³ of subsoil are proposed for reuse across the development.

A further complexity was the presence of coal tar material associated with former runway construction. Rather than defaulting to off-site hazardous landfill disposal, the project team explored a managed treatment and reuse route so that approximately 45,200 m³ of coal tar material could be repurposed as road subbase, subject to appropriate controls and approvals.

The Bespoke Materials Management Plan Framework

Omnia developed a phased Materials Management Plan framework designed to work within the CL:AIRE approach while reflecting the practical realities of a large, long-term development. The strategy uses one overarching MMP covering the outline red line boundary to establish the principle of reuse on the site of origin, supported by individual phase-specific MMP submissions as each reserved matters phase comes forward.

• Each phase-specific MMP is to be updated once the relevant reserved matters application, site investigation information and remediation strategy have been approved.
• Clean, naturally occurring surplus soils may be moved between phases where a defined need and suitable receiving area are demonstrated.
• Made Ground and impacted soils are managed within the phase from which they arise and reused only in accordance with the approved remediation strategy, such as beneath hardstanding or proposed cover systems.
• Where contamination is identified, materials are treated, managed or removed as required within that phase before reuse is considered.

Ground Conditions and Material Types

The general ground model comprises topsoil over superficial Brickearth, typically a sandy, gravelly silty clay, underlain by Raised Beach Deposits, typically fine to coarse sand, and then Upper Chalk bedrock. Discrete pockets of Made Ground were identified across the site, associated with historic uses, including coal tar beneath former runway areas. Materials considered within the strategy include topsoil, Made Ground, coal tar material, clay, sand and chalk.

Regulatory Engagement

Early engagement was central to the success of the strategy. Once the proposed route had been developed with the project Qualified Person, Omnia contacted both the Environment Agency and the Local Planning Authority by email to explain the constraints, the proposed phased approach and the safeguards that would be built into future MMP submissions.

The Local Planning Authority confirmed that it had no concerns with the proposal and agreed that a degree of flexibility was appropriate to enable the project to progress across multiple phases. No revisions were requested, and the approach was agreed by email, providing confidence that the project could proceed using a managed, transparent and regulator-aware framework.

Outcomes

Through the development of a flexible phased Materials Management Plan (MMP) framework, Omnia enabled the Ford Airfield project to progress despite each reserved matters phase being at a different stage of investigation, design and approval. The MMP strategy supports the sustainable retention and reuse of significant site-won material volumes, including upwards of 65,000 m³ of topsoil and 285,000 m³ of subsoil across the development, while also allowing approximately 45,200 m³ of coal tar material to be treated and repurposed as road subbase subject to appropriate controls. By using a bespoke Materials Management Plan approach, the project reduces reliance on imported materials and off-site disposal, helping to lower costs, reduce lorry movements and minimise environmental impact. The phased MMP framework also maintains clear governance through phase-specific Qualified Person review and CL:AIRE sign-off as each phase comes forward.

This project demonstrates the value of considering soil reuse early in the design process. By engaging with the client, Qualified Person, Environment Agency and Local Planning Authority at an early stage, Omnia was able to develop a measured and defensible strategy that maximises reuse while maintaining appropriate environmental safeguards.

The approach is particularly relevant to other large, phased developments where not all reserved matters phases are sufficiently advanced to support a single conventional MMP submission. It shows that, with early planning, suitable evidence and clear phase-by-phase controls, the principles of the CL:AIRE framework can be applied in a flexible way that supports sustainable development outcomes.

Background:

Omnia were commissioned by our client to undertake winter groundwater monitoring for the 2024/2025 winter groundwater monitoring period (October to April) at a site in the New Forest, Hampshire.

The site was proposed to be developed from agricultural land into residential dwellings. Winter groundwater monitoring was required to determine worst case groundwater levels at the site and to assist with drainage design.

Scope of Works

As part of the works, Omnia undertook an initial Phase II intrusive investigation in order to record the ground conditions at the site and to install the groundwater monitoring wells required for the monitoring.

Following the initial intrusive investigation, Omnia attended site in order to deploy groundwater level loggers to allow for groundwater levels on-site to be recorded at 1-hour intervals across the entire monitoring period. Omnia also undertook monthly spot monitoring visits to collect manual groundwater level readings to calibrate the continuous data collected.

Outcome

Omnia provided our client with a factual report of the works which included ground conditions encountered on-site, results of the monthly manual groundwater monitoring and the results of the continuous groundwater monitoring. The report identified areas of the site where shallow groundwater of less than 1.00m below ground level was recorded which could have an impact on shallow foundations and drainage solutions at the site.

Summary:

In 2023, Omnia were commissioned by the University of Central Lancashire (UCLan) to provide Geo-Environmental Consultancy Support on their campus in Preston, Lancashire. UCLan were proposing to build an extension to their Dentistry Facility, a process which included the demolition of an existing single-storey building and replaced with a larger extension

Scope of Works:

At the Dentistry in Preston city centre, our Geo-Environmental Consultants undertook a Phase I Desk Top Study followed by a Phase II Ground Investigation, to gather information of the underlying ground conditions including in-situ soil strengths. The aims of the investigation were to provide an assessment of risks posed to human health and controlled waters by shallow site soils, an assessment of risks posed by ground gasses, and to provide outline geotechnical assessment including presumed bearing capacities to assist with foundation design.

The site works comprised window sample borehole drilling in 5no locations and installation of 3no boreholes with monitoring pipework. 3no return gas/groundwater monitoring visits were undertaken.

Outcome:

Omnia carried out a human health risk assessment and a controlled waters risk assessment for the site and recommended that no further works were required in either case. Following completion of the monitoring programme, the ground gas assessment concluded that no specific ground gas protection measures were required. Omnia produced an outline geotechnical assessment for the site, including presumed allowable bearing capacities, concrete classification, and advice on floor slab design.

Summary

Omnia were commissioned by our client to undertake an intrusive site investigation at Ford Airfield in Arun, West Sussex. The site had historically been used as an airfield from 1918 up until 1980 with the military using the airfield during the Second World War up until 1958. Since 1980, the site was predominantly used for agriculture, but areas of the former runway are still present, as well as former Highways and Haulage yards.

The airfield is now the subject of a planning application to develop up to 1,500 residential dwellings as well as commercial and office spaces, a primary school, local centre and public open space.
The purpose of Omnia’s intrusive investigation was to provide information on potential sources of contamination on site as well as providing geotechnical characteristics of the soils beneath the site.

Scope of Works

Previous investigations had been undertaken at the site which were reviewed by Omnia, with areas requiring further investigation identified. Omnia identified the following areas where further investigation was required in order to obtain sufficient information:

• Geotechnical characteristics of the soils underneath proposed roadways.
• Geotechnical characteristics of the soils beneath proposed areas of residential development in the north and the south of the site.
• Chemical concentrations and composition of soils within areas of identified potential contamination sources. These areas included areas of the former runway, identified geophysical anomalies on-site, an infilled canal, the highways and haulage yards and an area of previously identified elevated concentrations.

The intrusive investigation was undertaken in October and December 2024 during which the following works were undertaken:

• Eighty-five trial pits were advanced to collect samples for CBR testing beneath proposed roadways to inform roadway design.
• Four Cable Percussion (CP) boreholes, thirty Window Sampling (WS) boreholes and thirteen trial pits were advanced to undertake in-situ geotechnical testing and to collect soil samples for laboratory geotechnical testing in areas of proposed residential development in the north and the south of the site to inform foundation design.
• Twelve WS boreholes, forty-nine trial pits, nine hand dug pits and four stockpile samples were advanced within areas of identified sources of potential contamination in order to obtain soil samples for chemical analysis and to determine the vertical and lateral extent of any visual contamination.

Ground conditions within all locations were logged and recorded in accordance with British Standard BS5930 by an Omnia engineer.

Outcome

All CBR data obtained from soils beneath the proposed roadways was reported to Omnia’s client via a Factual Report which could be used to inform the appropriate design of the roadways.

Interpretive reports were produced detailing the ground conditions encountered and the results of the in-situ and laboratory geotechnical testing within the two areas of proposed residential development. The reports included proposed design bearing capacities for foundation design, concrete classification of on-site soils and recommendations for further works.

A detailed interpretive report, including a Tier 1 risk assessment based on residential end use, was produced detailing the ground conditions encountered and the results of the laboratory chemical analysis of soils within areas of identified potential sources of contamination at the site. Elevated concentrations of contaminants were recorded in multiple areas across the site and the report included an analysis of the elevated concentrations and recommendations for further works required.

Next Steps

Based on the findings of Omnia’s intrusive site investigation on this site in West Sussex, we have recommended to our client that further investigation is required in areas of the site to determine the extent and potential impact of identified contamination. Where the extent of contamination has been suitably determined, it has been recommended that remediation is undertaken, following a remediation method statement, to make the site suitable for use.

Summary

Omnia were commissioned by our client to assist with an intrusive site investigation being undertaken on an industrial estate in St Peter Port, Guernsey. Our client requested Omnia’s support in supervising the proposed intrusive investigation and producing a Phase II Geo-Environmental and Geotechnical report to support a planning application for the construction of five industrial units and associated infrastructure. 

The site comprised a number of buildings used for commercial/industrial purposes and was located within the footprint of a historical clay pit for a brickwork located nearby. As such, the ground beneath the site was assumed to comprise Made Ground overlying natural bedrock deposits. 

Scope of Works

The intrusive site investigation was undertaken in September 2024 during which the following works were undertaken: 

• Eleven window sampling boreholes were advanced to a maximum depth of 6.00m below ground level to allow for the logging of shallow soils, undertaken in-situ SPT testing and collection of samples for chemical and geotechnical testing. 

• Four trial pits were advanced to a maximum depth of 1.50m below ground level to allow for the logging of shallow soils and the collection of samples for chemical and geotechnical testing. 

• Follow on soakaway testing was undertaken within two of the trial pits. 

• Follow on gas monitoring within four monitoring wells which were installed during the intrusive investigation. 

Outcome

An interpretive report was produced for the client detailing the ground conditions encountered during the site investigation and the results of the in-situ and laboratory testing. Made Ground was encountered within all locations across the site associated with the historical clay pit and subsequent infilling. The full thickness of the Made Ground beneath the site was recorded in only five of the locations and was recorded up to a maximum thickness of 5.40m. 

As part of the report, Omnia undertook a Tier 1 Risk Assessment based on the proposed commercial end use which identified levels of asbestos fibres in the Made Ground which had the potential to cause significant harm to future site users. Omnia recommended that remediation measures are undertaken, following a remediation method statement, to make the site suitable for use. 

Based on the results of the ground gas monitoring undertaken, a potential risk to future site users was identified. In order to determine the extent of the risk and the magnitude of any protective measures required on site Omnia have been commissioned by our client to undertake a further ground gas monitoring visits including the analysis of the collected data and recommendations for any protective measures. 

Additionally, preliminary foundation options were provided to the client based on the ground conditions encountered and SPT N value collected during the intrusive works.