In this blog we are taking an in-depth look at UXO surveys, exploring what they are, why you might need one and how you can book a survey at Brimstone UXO.

What is a UXO survey?

A UXO survey is a specialised site-based service designed to explore beneath the surface and detect buried ferrous objects which could be items of unexploded ordnance. This crucial step in the pre-construction phase helps ensure the safety of groundworks by assessing and mitigating the risk of encountering UXO. Brimstone offers both intrusive and non-intrusive UXO surveys, utilising cutting-edge equipment to provide surveying solutions for all construction and development projects.

As sites have varying requirements due to accessibility, previous land use, and soil depth, Brimstone collaborates closely with clients to determine the most suitable method, aligning with project budgets and time constraints. This meticulous approach ensures planned groundworks proceed safely, with the risk of encountering unexploded ordnance reduced to as low as reasonably practicable (ALARP).

What is a uxo survey

Do I need a UXO survey?

A UXO survey usually follows a UXO risk assessment and is undertaken before any ground intrusion works on sites with a moderate or high UXO risk.

If a UXO survey is recommended for your site, it indicates a potential risk of UXO contamination, which could range from unexploded bombs dropped by the Luftwaffe (German Air Force) to contamination from Allied military activity such as weapons manufacturing or training exercises.

While there isn’t any legislation in the UK defining the steps you must take to check for UXO before beginning any construction or development work, there are legal obligations under the Health and Safety at Work Act 1974 and the Construction Design and Management Regulations 2015 to ensure the health and safety of employees. UXO surveys not only ensure the safety of construction workers and the public but also prevent expensive, unexpected costs and delays from disrupting your project further down the line.

Non-intrusive UXO surveys

Efficiently clearing large areas up to 6 metres in depth, non-intrusive UXO surveys are ideal for greenfield sites or areas where ground disturbance must be minimised. Brimstone offers three types of non-intrusive survey: pushcart, towed-array, and drone.

These surveys excel in pinpointing shallow-buried UXO items, including land service ammunition. They leverage magnetometry to detect ferrous materials, mapping magnetic signatures through fluctuations to identify ferrous objects.

Pushcart UXO surveys
A pushcart UXO survey is a five-channel system for detecting ferro-magnetic anomalies in small to medium sized areas. This survey is carried out by a specialist two-person team who manually push the system over the area of land being surveyed.

Towed-array UXO surveys
A towed-array UXO survey is an eight-channel gradiometer system that detects ferro-magnetic anomalies in large areas. Again, this survey method is carried out by a specialist two-person team and involves towing the sensors behind an all-terrain vehicle. The wider sensor array increases time efficiency without detriment to resolution or quality.

Drone UXO surveys
A UXO drone survey enables us to carry out surveys in areas where a pushcart or towed-array system cannot reach. The UAV is used as a platform for sensors and detectors, enabling our engineers to fly them over extensive areas of land searching for signatures of unexploded ordnance. They are equipped with state-of-the-art Lidar, Photogrammetry and Magnetometry systems which enable precise 3D models to be captured, along with detailed terrain mapping and high-resolution imagery.

Our drone systems routinely deliver superior survey coverage, surveying up to five times as many hectares in a single day compared to the push-cart system. Drone systems are also highly suited to difficult to access areas or areas where ground disturbance must be minimised.

Intrusive UXO surveys

Tailored for detecting deep-buried bombs, intrusive surveys are ideal for brownfield land or areas with made ground. Achieving greater depths compared to non-intrusive methods, this survey method provides detection and clearance ahead of individual pile locations, clusters, and borehole works.

Intrusive UXO surveys are achieved through a Cone Penetrometer Testing (CPT) rig, which is a boxlike container that is mounted on a crawler undercarriage, ideal for traversing challenging terrain which can be common on construction sites. At Brimstone we have three CPT Rigs, called Honey Badger, Redfox and Handsome.

An intrusive UXO survey involves a CPT rig pushing a magnetometer probe into the ground using hydraulic pressure to survey a column of soil. It then uses magnetometry to identify fluctuations caused by ferrous metals, which could be UXO.

Our rigs enable us to survey single pile positions or clusters for any deep intrusive works. For large scale excavations, we can provide a site-wide matrix clearance, offering complete surveying solutions to a maximum depth of 25 metres across a large area. Our system is triaxial, meaning it models targets in three dimensions, which allows more than one pile position to be cleared per one survey position, reducing the overall number of surveys required.

When you book an intrusive UXO survey at Brimstone, our team will ask for a drawing of the proposed pile layout so we can calculate the minimum number of surveys that would be required to cover each pile location. On sites where there is dense made ground, we might require pre-drilling for the survey positions. This is because our probe can’t push through ground that has brick or concrete fragments. If this is required, our team will liaise with you directly to get this organised.

Intrusive uxo surveys at brimstone

Marine UXO surveys

UXO surveys can also be undertaken in marine environments. A seamless integration between sonar and magnetometer data ensures that your project can go ahead with minimum delay and downtime.

A Side Scan Sonar can be used to create a high-resolution image of the seabed, regardless of water clarity. Capable of detecting objects to 0.2m in length and covering 100m in a single sweep, this system is a cost-effective and efficient method to accurately identify seabed anomalies.

Similar to intrusive and non-intrusive surveys, magnetometry is also used for marine UXO surveys to detect ferrous objects either buried or lying on the seabed. This is commonly used for ferrous marine UXO but is also capable of detecting cables, pipes, fishing gear and any other ferrous debris that may cause an obstruction to your operations. Multiple magnetometer configurations can be deployed depending on your project requirements. The data from both the magnetometer survey and side scan sonar can be integrated with other geophysical datasets to provide a full seabed interpretation suitable for multiple engineering projects.

All of this is made possible thanks to our fully fitted Remotely Operated Vehicle (ROV) fleet which is equipped to carry out comprehensive marine surveys and precise target investigations. This versatile option can be operated from a vehicle parked on the dockside, on a barge, or on a survey vessel, making it suitable for a multitude of marine environments.

Marine uxo

Data processing and interpretation

Following the UXO survey, the collected data is sent back to our in-house geophysics team at Brimstone’s Head Office for processing and interpretation.

For non-intrusive surveys, multiple steps are taken to reduce noise and improve survey quality before a magnetic field false colour map is generated highlighting any ferrous anomalies. In intrusive surveys, real-time data logs are saved and processed, with extensive cleaning, filtering, and correction processes employed to refine the dataset.

Through these rigorous procedures, analytical signals are selected. We use a specialist computer model to look at these signals and compare them against a bank of known UXO signals. Using our bespoke software, our team can make estimations of the depth and mass of any suspected item, along with its location in coordinates accurate to 5 centimetres.

What happens with the UXO survey results?

Once the UXO survey results have been reviewed, we provide our clients with a detailed report outlining the survey findings and any recommended further action.

If there are targets that require investigation, we will recommend that our engineering team is deployed back to site to carry out a target investigation, and that no intrusive works start on site until this has been carried out.
A target investigation involves our engineers uploading the coordinates to a GPS system to pinpoint the identified targets on site. They then use hand tools to unearth the targets and lean on the resources of excavators for significantly deeper targets. If we find any items of ordnance, you’re in safe hands, as Brimstone is a licensed UXO disposal contractor.

While we have the licenses and capability to dispose of items of ordnance, we will usually lean on the resources provided by the British military to keep costs as low as possible for our clients initially. However, if required, Brimstone can carry out high and low order demolitions in complex environments to tackle all explosive ordnance contamination projects.

If the survey date results in no anomalies being found, and there are no further recommendations for UXO risk mitigation, you can continue with peace of mind that your groundwork can be carried out safely and that you have mitigated the risk of UXO. We will also provide you with a UXO ALARP certificate.

How to book a UXO survey at Brimstone

At Brimstone, we care about your development as if it was our own. Our deep industry knowledge, UXO expertise and ongoing investment in technology make us the logical choice for your safe build.

If you have already procured one of our UXO risk assessments and this results in the recommendation of a UXO survey, our team will begin the discussion regarding this as soon as you have received the survey report.

If you have received a UXO survey recommendation from another UXO company, you can easily book our services by calling our Commercial Team on 020 7117 2492 or by emailing

For us to fully understand your requirements, the team will request a few key pieces of information, such as the site location, a redline boundary, details of the proposed development works and the scope of the survey required, if you know what you need already.

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