Deep detection. Absolute confidence.

Surface magnetometry has a reliable detection limit of approximately 4–6 metres. Where proposed foundations, piles, or deep excavations penetrate beyond that depth, particularly in soft ground such as clay or peat where WWII bombs can reach 12 metres or more. In these cases, a non-intrusive survey cannot provide the required assurance. An intrusive CPT survey uses a hydraulically-pushed probe to scan the soil column to the assessed maximum bomb penetration depth, delivering reliable detection well beyond any surface method.

A Cone Penetration Testing rig pushes a magnetometer probe into the ground using hydraulic pressure from a tracked crawler unit. As the probe descends, it continuously logs magnetic field data at depth, detecting the ferrous signature of buried ordnance in real time. The rig can reach depths exceeding 25 metres in suitable soil conditions, and modern triaxial systems can model anomaly geometry in three dimensions to help distinguish UXO from scrap metal.

An intrusive survey is recommended where: proposed works exceed the assured detection depth of surface magnetometry; the site has soft or deep-fill ground; a Detailed Risk Assessment has rated the site at moderate or high risk; or a non-intrusive survey has identified priority anomalies that need resolution before construction can proceed. It is also commonly used for individual pile or borehole positions where point-specific clearance is required.

A compact urban site with 50–100 pile positions can typically be completed in one to three days. The rig footprint is small; crawler-mounted units are designed for constrained urban plots, and the process causes minimal ground disturbance compared to traditional trial pitting. Exact target locations are recorded to centimetre accuracy, and real-time data means anomalies can be flagged and responded to immediately on site.

You receive a detailed technical report including all probe logs, the location and estimated depth and mass of any anomalies detected, and a site plan. Where no anomalies requiring further investigation are identified, an ALARP certificate confirming that UXO risk has been reduced to as low as reasonably practicable is issued for the surveyed positions. This document is suitable for submission to your CDM file, insurer, or planning authority.

If a significant ferrous anomaly is detected, the probe is withdrawn and the position is flagged for target investigation. A trained EOD engineer directs a supervised excavation at that location to identify the object. The vast majority of anomalies prove to be scrap metal, construction debris, or geological variation. The protocol ensures any genuine find is managed safely before construction equipment returns to that position.