Brownfield Development in the Midlands – Constraint, Risk or Opportunity?

by Libby Choularton | Aug 12, 2026 | Article

Brownfield Development in the Midlands – Constraint, Risk or Opportunity?

For developers looking at the Midlands, the question is no longer whether brownfield land will form part of the delivery pipeline. It is whether the risks associated with these sites are being understood early enough to turn constraint into opportunity.

As with the rest of the country, the Midlands is under increasing pressure to deliver new homes, regenerate towns and cities, and support economic growth. At the same time, the availability of straightforward development land continues to diminish and what is there becoming harder to secure, resulting in brownfield sites becoming increasingly important – moving from the difficult option to an essential part of the regional pipeline.

This direction of travel is also reflected in national and regional policy. Government guidance continues to emphasise the reuse of brownfield land, with funding streams available to help unlock stalled housing-led sites, including remediation, enabling works and infrastructure. In the Midlands, combined authorities are also actively promoting brownfield regeneration as part of wider housing and economic growth strategies.

Omnia sees this as a positive. Some of the best development opportunities in the Midlands are on previously developed land: sites that are often well connected, close to existing infrastructure and located where investment can have a direct impact on local communities.

Yet despite the obvious benefits, brownfield development is still frequently viewed as being too difficult, too risky or too expensive. That perception is understandable but it can also prevent good sites from being properly assessed.

Constraints Don’t Prevent Development

One of the most common misconceptions in our industry is that environmental or geotechnical constraints make a site unviable.

The reality is that very few sites are completely without constraints. Whether you are developing a greenfield site on the edge of a settlement or bringing forward a former industrial site in the heart of a town, there will always be challenges to overcome. The difference with brownfield land is that the challenges are often more visible, or at least more anticipated.

Former industrial uses, historical mining activity, made ground, contamination, ground gas and groundwater issues are all common across many parts of the Midlands. However, their presence does not automatically mean a site cannot be developed.

Missed Opportunities on Brownfield Development

Too often, sites are discounted early because potential constraints are perceived as too difficult to address. While that approach may seem sensible, it can result in missed opportunities.

As developers face increasing competition for land, rising costs and ambitious housing targets, the sites that remain available are often those requiring a greater degree of technical understanding and innovation. In many cases, the value lies not in finding the perfect site but in identifying a site where challenges can be understood, priced, managed and engineered through the right strategy. The organisations that will succeed in the coming years are likely to be those willing to take a more informed view of risk rather than simply avoiding it.

Value Engineering Starts Below Ground

When people hear the phrase ‘value engineering’, they often think about foundations, materials or construction methods. In reality, some of the greatest opportunities for value engineering occur before a design has even been finalised.

A detailed understanding of ground conditions can fundamentally influence how a site is brought forward. From earthworks and remediation strategies to foundation design, drainage solutions and material management, early technical input can reduce uncertainty, test assumptions and identify opportunities that may otherwise have been overlooked.

We have seen sites initially considered problematic become highly successful developments because the right investigations were undertaken early and design decisions were informed by robust data. Equally, we are aware of sites where assumptions were made too early, resulting in avoidable costs later down the line. The difference is rarely luck, and usually a case of sourcing and using information effectively.

Brownfield land will play a major role in the future of Midlands development

The Midlands has a proud industrial heritage, and many of the sites that can support future growth are a direct result of that history. If developers are serious about delivering housing, supporting regeneration and making better use of available land, then the industry needs to become more comfortable working with complexity.

The industry sometimes underestimates what can be achieved when developers, engineers, environmental consultants and planners collaborate early enough in the process. The question should not be about whether a brownfield site contains challenges; most do. Instead the question should be about how those challenges can be understood early enough with the right expertise to unlock its potential.

Looking Beyond the Constraints

Across the Midlands, significant opportunities sit behind perceived constraints. The developers best placed to unlock them will be those who invest early in understanding risk and are prepared to use technical insight, not assumption, to shape their strategy.

At Omnia, our teams have experience working on complex brownfield sites where ground risk, contamination and development viability need to be considered together. If you are assessing a constrained site, we are happy to have an early conversation about the risks, opportunities and engineering options that could help unlock its potential.

Coal Mining Risk Assessments

CMRA – County Durham

Geo-Environmental Consultancy – Lancashire

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Is there a Coal Mining Risk in Southern England?

by Libby Choularton | Jul 28, 2026 | Article

Is there a Coal Mining Risk in Southern England?

When Coal Mining is discussed, most people think of the coalfields in South Wales or The Midlands and some maybe thinking of the northeast or Scotland, with the map of coalfields in figure 1 showing the reason for this.

However, whilst the majority of coal mining areas are indeed located in South Wales the Midlands, The northeast and Scotland, coal mining did also occur in the south at several coalfields, located in Kent, Bristol & Somerset, and Devon.

In addition to these, there is also a coalfield beneath Oxfordshire although this has never been commercially exploited due to its combination of depth (300m-1,500m), thin seams and low quality coal and as such does not present a risk of mining induced subsidence.

The southern coalfields are covered by the Mine Remediation Authority (former Coal Authority) Reporting Areas, as shown in figure 2, and developments within these areas will require a Coal Mining Risk Assessment (CMRA) to be completed as part of the planning process.

However, in addition to coal mining, the south also has a legacy of non-coal workings including:

Chalk & flint
Building stone (sandstone & limestone)
Brick Clay
Metals (tin, copper, lead & arsenic)

Key Takeaways

Yes, there is a coal mining risk in some areas of the south.

There are also non-coal mining risks in the south.

Ground risk assessments should be based on evidence, not assumptions about location.

If you’re working on sites in the south, it is worth asking what is beneath the surface.

Figure 1 – UK Coalfields Map

Figure 2 – Mining Remediation Authority Reporting Areas in the South

Figure 1 – UK Coalfields Map

Figure 2 – Mining Remediation Authority Reporting Areas in the South

However, in addition to coal mining, the south also has a legacy of non-coal workings including:

Chalk & flint
Building stone (sandstone & limestone)
Brick Clay
Metals (tin, copper, lead & arsenic)

Key Takeaways

Yes, there is a coal mining risk in some areas of the south.

There are also non-coal mining risks in the south.

Ground risk assessments should be based on evidence, not assumptions about location.

If you’re working on sites in the south, it is worth asking what is beneath the surface.

Coal Mining Risk Assessments

CMRA – County Durham

Geo-Environmental Consultancy – Lancashire

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Adrian King

Principal Geo-Environmental Consultant

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Your Material Management Plan is in Place – What Next?

by Libby Choularton | Dec 1, 2025 | Article

Your Materials Management Plan is in Place – What Next?

What is a Materials Management Plan?

A Materials Management Plan (MMP) can allow the re-use of contaminated or uncontaminated soil, Made Ground and other material in earthworks without the requirement to go through the lengthy and costly process of obtaining an environmental permit. The CL:AIRE Definition of Waste Code of Practice (DoWCoP) was developed to provide a simplified process to enable the re-use of site-won materials (‘waste’ and non-waste), either on the site of origin, or on another nominated site without the need for an Environmental Permit.Once your Material Management Plan is in place, the next step is ensuring soils are tracked, recorded, and verified correctly so your project remains compliant and avoids unnecessary delays or regulatory issues.

Managing Soils On-Site

Once you have the Materials Management Plan in place, it’s easy to think of it as just a bit of paperwork that can sit in the drawer or filed away on-site. That is not the case, and the methodology for tracking and managing soils on-site needs to be followed. Due to the implications of not correctly managing soils, we are finding more and more that people seem to be so scared of doing it wrong, that they don’t want to try to do it right in first in place!

Hopefully through this blog post, we can dispel some on the common fears and demonstrate how managing and tracking soils on-site can be easy.

Regardless of the complexity of your soil re-use, the principles of managing the soils remains the same.

Plan

As well as having your Materials Management Plan in place to demonstrate that soils are suitable to be re-used on-site, it is important to also have a plan on how you are going to track these soils.

One of the most effective methods of tracking soils is to implement a grid-based system across the site. The grid squares can be as large or small as they need to be depending on the complexity of your site.

For example, if it’s really important that soils from 1 corner of the site are only re-used in another small area, it would be better to have smaller grid squares. Whereas if you are only re-using clean materials, and they can be used anywhere on the site, it would be practical to have larger grid squares that represented close to the amount of soils that could be moved per day.

Once you have your grid system decided, you will also need to set up a tracking form to record where materials have arisen from, where they are stockpiled, and where they end up. You can also use this form to record any required testing, import tickets and disposal tickets.

Track

The purpose of the tracking form is to clearly demonstrate where materials have come from, and where they have been placed. To ensure your soils are tracked the whole way through a project, it is key to decide who is going to be responsible for completing the tracking form. This ensures it doesn’t just fall through the cracks with everyone assuming someone else will pick it up.

Drone Surveys/Photographs

Using Drone surveys on-site is becoming more and more popular and is a great way of recording what is happening on-site at a given time. When you compare weekly drone photographs of the site, it is easy to see how things have evolved on-site over time. You can use these images to document your stockpiles and soil re-use, by annotating them and linking them back to the tracking form.

Recording movements on-site doesn’t have to be as high-tech as using a drone though. You might have weekly site meetings where you print out a large drawing of the site and draw on where your stockpiles are, what areas are completed, where soils are due to be cut etc. This method is just as effective, you just need to keep a record!

They key with whatever method of tracking you use, is that it needs to be simple, and a small addition to the works the developers are already doing. It is very likely that they are already recording the information needed for managing soil reuse under an MMP.

Audit

Throughout the soil movement phase of works, it can be helpful to have a 3^rd party (such as Omnia) review your records to advise on the information that is being recorded, and to also offer guidance and advice of any problems that may have arisen.

It can be helpful to start the process with a pre-start meeting to discuss the requirements with all parties who will be involved on-site, and come up with the most appropriate tracking system for your site.

Verification & Reporting

Once all the soil movements are complete, you will need to “close out” the MMP with CL:AIRE, which can only be done by submitting a Verification Report.

The CL:AIRE Definition of Waste Code of Practice (DoWCoP) sets out the following will be needed within a Verification Report:

Appropriate site plans;
Experience and qualifications of the person preparing the report in relation to the specific project;
Description of the project;
Description of how the use of materials links with the Remediation Strategy or Design Statement (which should be set out in the agreed MMP already);
Reference to site investigation data if applicable (which should be set out in the agreed MMP already);
Reference to risk assessments (including qualitative risk assessments) (which should be set out in the agreed MMP already);
Reference to the MMP and associated tracking system, including alterations made and why;
Suitable for use criteria;
Treatment records (if applicable);
Laboratory analysis (if applicable);
Reference to waste transfer documentation, including return loads (if applicable);
Signed delivery tickets (if applicable);
Record of contingency arrangement(s) that had to be implemented;
Record of quantity of materials used (this can be calculated using a pre start and post completion topographic survey); and
Copies of signed Declaration(s) by Qualified Person(s).

If you do not submit a Verification Report for your MMP, the project could be considered “non-Compliant” and the imported/excavated/reused material could potentially be considered as an illegal deposit. CL:AIRE may share such data with the EA / NRW and HMRC.

If you have a site that might require an MMP or an MMP Verification, get in touch with our team to discuss, we are always happy to help.

References:

Waste Framework Directive (2008) Directive 2008/98/EC of the European Parliament and of the Council of 19 November 2008 on waste and repealing certain directives
CL:AIRE (2011) Definition of Waste: Development Industry Code of Practice Version 2

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Olivia Maxwell

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Sinkholes and Karstic Risk

by Libby Choularton | Aug 7, 2025 | Article

Sinkholes and Karstic Risk

Sinkholes received a significant amount of coverage in the media in February 2025 due to the sudden appearance of a sinkhole (approximately 20m long, 5m wide and 5m deep) in Godstone High Street, Surrey which led to the evacuation of 30 households.

What is a Sinkhole?

A “sinkhole” is generally defined as “a saucer-shaped hollow that is the result of some kind of collapse or removal of an underlying layer of rocks that used to support the layer of material at the surface.” (BGS)

How do Sinkholes Form?

Most sinkholes result from natural geological processes, generally involving water, where rock or soil from below the surface layer is removed leaving the surface layer unsupported.

In areas underlain by a carbonate bedrock (chalk/limestone/dolerite), salt deposits (halite) or other soluble rocks such as gypsum, percolating water dissolves the rock over time leaving underground fissures and voids which can suddenly collapse.

What can cause a Sinkhole?

Sinkholes can appear rapidly and without any apparent warning and so it is very important that consideration is given to the potential for sinkholes to form at the planning stage to facilitate a thorough investigation and allow the mitigation of any associated risks.

The gradual process of dissolution can cause a sinkhole to be form at ground level, but due to the long timescales involved these sinkholes may have historically yielded a surface depression which has been subsequently lost through the infilling of surface hollows.

Rapid sinkhole appearance is generally tiggered by one of the following causes:

Heavy Rain/Flooding – can be responsible for the collapse of cavities which are normally stable, particularly if the cavities are developed within superficial deposits;
Water Leaks – Leaking drains, burst water mains and irrigation can all trigger the formation of a sinkhole with burst water mains commonly cited as the cause of sinkholes in media reports;
Building Works – Changes to surface drainage, including the construction of soakaways, or changing the loading of the ground by building or cut/fill works can all trigger sinkhole formation;
Changes in Water Table – groundwater provides buoyant support to cavities and so lowering of the groundwater level for excavation dewatering or water abstraction can cause these cavities to collapse as the voids empty of water.
Mining/quarrying – can trigger sinkhole formation through:
- Dewatering
- by intercepting clay filled voids which subsequently collapse;
- the collapse of shallow open tunnels, often triggered by heavy rain or water leaks.

Different types of Sinkhole

There are three main types of sinkhole:

Dissolution sinkholes

Formed by the chemical weathering of the underlying rock where surface water drains through a fissure/joint in the rock which over time gets enlarged with the subsequent hollow being drained through the fissure/joint. These depressions tend to form gradually;

Collapse Sinkholes

These form where the gradual collapse of an underground void occurs and triggers subsidence at ground level although these sinkholes can form rapidly as a response to the rapid influx of water. Depending on the depth of the original void, these collapses may or may not show a surface depression;

Suffofusion Sinkholes

These sinkholes form where dissolution causes a depression on the bedrock surface beneath a covering of soil. The unsupported soil then subsides forming a depression at ground level. These features tend to form gradually if the covering material is sandy, but can appear suddenly where the material is more cohesive which can allow quite a large cavity to form before collapsing.

Where do Sinkholes Form?

Natural sinkholes most commonly occur in areas underlain by soluble rocks which form karst and which include salt deposits (halite), gypsum, chalk, limestone and dolerite.

More information on where Karst is present can be found in the recently published BGS Karst Report Series.

Sinkholes associated with classic karst landscapes form in areas underlain by Carboiniferous limestone including the Mendips, parts of Wales, Peak district, northern Pennines and Yorkshire Dales.

Areas underlain by the Permian gypsum deposits in northeast England are particularly susceptible to the formation of sinkholes, with the Ripon area being particularly prone to large sinkholes.

Areas underlain by salt deposits are also susceptible although in these areas brine extraction make it difficult to separate natural from manmade sinkholes.

Finally, the Chalk deposits underlying much of the southeast are prone to the formation of sinkholes, with up to 97% of Chalk sinkholes occurring where there is a younger cover deposit over the White Chalk with areas in the vicinity of the Chalk/Palaeogene boundary being of particular concern.

Winter Ground Water Monitoring

Site Investigation & Foundation Design

Phase 1 DTS

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Coal Mining Risk Assessments

by Libby Choularton | Jul 9, 2025 | Article

Coal Mining Risk Assessments

What is a Coal Mining Risk Assessment?

A Coal Mining Risk Assessment (CMRA) is a report that considers the legacy coal mining activities beneath a subject site and within the local area, to assess the potential hazards which could present a significant risk to the proposed development. A CMRA is a desk-based study which analyses published records from the likes of the British Geological Survey and Mining Remediation Authority to gather an understanding of the complex geology and assess its economic potential as a historic resource.

Coal Mining Risk Assessments and Planning

Coal Mining Risk Assessments (CMRA) are often stipulated as a planning condition by multiple local authorities across the United Kingdom where the proposed development falls within a Mining Remediation Authority (MRA) ‘Development High Risk Area’ and where the MRA would be a consultee. Should the subject site not fall within a ‘Development High Risk Area’ and only a ‘Coal Mining Reporting Area’ a full CMRA may not be required. However, this will need to be assessed on a site by site basis.

Image by Mining Remediation Authority

Where are the Mining Remediation Authority ‘Development High Risk Areas’?

Mining Remediation Authority ‘Development High Risk Areas’ are sporadically spread across Mining Remediation Authority ‘Coal Mining Reporting Areas’. The ‘Coal Mining Reporting Area’ are located within areas of historical coal mining activity and importantly, coal bearing geological formations. ‘Coal Mining Reporting Areas’ are primarily located in the Midlands, North East and North West of England. Other notable areas of coal mining include Kent, Bristol, South Wales, and the Lowlands of Scotland.

What are the Hazards Associated with Coal Mining Legacy?

Historical coal mining activity can present both geotechnical and environmental liabilities towards any proposed development.

Geotechnically, historical coal mining can pose different issues which can affect the stability of any proposed development often through coal seam and mine shaft collapse resulting subsidence of a developmental platform. Mine shaft collapse can also pose a significant risk to human health should a deep void open at surface.

Historical coal mining activity can often leave behind high levels of contaminants such as heavy metals, sulphates and hydrocarbons which pose a risk to both soils and groundwaters beneath a subject site. In order to assess the specific risks associated with historical coal mining on a proposed development, ground investigation is often required. Which can be undertaken along side other ground investigation activities.

Disused coal mines can often provide a preferential pathway for hazardous mine gas such as methane and carbon dioxide to flow to the surface. Unless properly mitigated against these gases can cause significant risk to a proposed development and human health and can cause asphyxiation and explosions of the flammable gases.

Furthermore, disused coal mines can also provide a preferential pathway for contaminates at surface from both coal mining activity, other current and historical uses associated with the subject and surrounding area to migrate towards groundwater resources.

How to carry out a Coal Mining Risk Assessment

A Coal Mining Risk Assessment (CMRA) is a desk based assessment of ground stability and mining-related hazards which are posed by historical coal mining activity. A CMRA must be undertaken by a suitably academically and professionally qualified person. A CMRA should include an assessment of up-to-date third party information held by the British Geological Society and Mining Remediation Authority to understand the complex geological model beneath the subject site and the likelihood of hazards presenting a risk to any proposed development from the mining of coal.

Is a site investigation needed after a CMRA?

Following the undertaking of a desk based Coal Mining Risk Assessment it may be necessary to undertake a physical ground investigation depending on the risks associated with an individual site. The requirement of a ground investigation, the amount and the type of investigation needed will be specific to the risks associated with the proposed development.

Ground investigations can often include the investigation of shallow coal seams through the advancement of boreholes to anticipated target depths, trial pitting and probing to identify mine entries. However, in order to undertake a ground investigation that may disturb coal seams, abandoned mine workings or mine entries a ‘Coal Permit’ is legal requirement.

The permit ensures that all operations in a coal field are conducted safely and in compliance with regulations to protect the public and environment.

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Changes to UK Radon Maps

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Slope Stability Assessments

by Libby Choularton | Mar 12, 2025 | Article

Slope Stability Assessments

What is a Slope Stability Assessment?

A slope stability assessment is exactly what it says – it is the assessment of the stability of a slope. Or how likely is the slope to fail if conditions change – conditions such as greater loading on the slope (foundations or pavements etc.) or a change in the pore water pressure (if it becomes saturated etc.) or if a natural or man-made slope is made steeper.

A range of testing and calculations are undertaken to determine, essentially, if the slope is too steep for the proposed end use or if the existing slope could be at risk of failing.

What is Slope Failure and what Causes Slope Failure?

The term fail can be slightly ambiguous or subjective when looking at slope failure. It can mean a slight slippage of the slope where a section slides slowly down. It can mean a significant slippage where a large portion of a slope collapses – in extreme circumstances think mudslide.

There can be a number of causes of slope failure and understanding this is an important factor in the assessment of potential failure or of a slope that has already failed.

Increase in pore water pressure – think saturation of the soils or material the slope is made up of. There are voids or cracks and fissures in the soils that make up pretty much all natural and engineered slopes. These may be tiny ‘pores’, but as water fills these pores, combined with gravitational effects, the pressure increases to a point where the matrix holding the particles together break apart and create a slip plane and the soil to collapse. A simple example of this might be building a sand castle then watching it collapse when you pour water.

Greater loading on the slope – essentially, the heavier the load placed on the ground at the top of a slope, the more likely it will destabilise. To achieve a stable slope, the shear strength of the soil must be higher than the shear stress, which includes the weight added to top of the slope. The load can include buildings, roads, vehicles etc. The further from the slope’s crest the load is, the higher the possibility of preventing slope failure

Types of Slope Failure

The most common type of slope failure is rotational failure (or rotational slide) which is identified when failed soils move outwards and downwards. There are three types of rotational failure – face, base and toe failure.

Translational failure occurs when adjacent areas of soils of differing strength slide pass each other. The sliding mass often travels long distances before coming to rest.

Compound failure is a combination of rotational and translational. This generally occurs when the surface curves at both ends but maintains a flat central point. This distinctive topography is a primary indicator of a compound failure.

A flow slide occurs when soils behave like a fluid which spreads across and down even very shallow slopes.

Wedge Failure (or block failure) occurs when weak layers, joints and fissures are broken apart and material moves down the slope in wedges or blocks.

Phases of a Slope Stability Assessment

The first step in any geotechnical project, including slope stability assessments, is a Phase I Desk Top Study. This will include a review of available geological information and history of the land use. Omnia will also recommend completing a site walkover to visually inspect the slope and commission a topographical survey to obtain accurate measurements of the land. If our engineers can’t access the slope, a drone can be employed to survey the area and assist with the walkover.

Following the completion of the desk study, a geotechnical site investigation will be conducted. The aim of this investigation is to determine the materials that make-up the slope and surrounding ground, and to establish groundwater conditions. The quality of data from the ground investigation can be critical and it is essential that a well scoped and robust set of investigation and testing is completed, as the parameters used in the assessment are derived here. Getting them wrong can cause a bit of an issue down the line.

Access on to the slope is also key here. Assessing an existing slope for integrity or to determine a re-grade/design parameters will need information from the slope itself, which often comes with challenges – walking up some slopes can be difficult, let alone putting specialised plant on to it. This can become even more of a challenge if dealing with remediation of a failed slope.

Omnia have experience in planning and executing these type of complex investigations and are fortunate enough to have a strong and diverse supply chain able to support us in completing even the most difficult access projects.

Using the findings from the site investigation, and taking the time to understand the client’s requirements, our consultants will conduct a slope stability analysis to the requirements of EC7. The subsequent report will include all findings from the investigation and present a suitable set of design documents appropriate for the project in hand. This might include re-profiling as part of access creation or level adjustment, design drawings as part of an earthwork construction, broader assessment to support a cut and fill exercise. It might include a completely revised design to assist in the remediation of a failed slope including recommendations to rectify and prevent further failure.

Our consultants have the knowledge and experience to assist with slope stability assessments across the UK. Please get in touch with our team if you have any questions or you would like us to take a look at your site.

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