Detect threats before you touch the ground.

A non-intrusive survey uses surface magnetometry to detect buried ferrous metal objects without disturbing the ground. Sensors are passed systematically across the site and measure variations in the Earth's magnetic field caused by metallic objects below. The data is then processed and interpreted by a specialist to identify anomalies that may be UXO, distinguishing likely targets from general scrap metal or geological noise.

Standard ground-based magnetometry provides reliable detection to approximately 4 metres below the surface, with some systems capable of assurance to 6 metres depending on soil conditions and instrument configuration. Where proposed works go deeper (for example, piled foundations or deep basement excavations), an intrusive CPT survey will be required to provide assurance at greater depth.

Ideally early in the pre-construction phase, once a Detailed Risk Assessment has confirmed that a physical survey is required. Conducting the survey before any site clearance, topsoil stripping, or utility trenching ensures maximum data quality. Early results also allow anomaly investigation to be programmed efficiently alongside other enabling works, minimising disruption to the programme.

Duration depends on site area, ground conditions, and access constraints. A compact brownfield plot of a few thousand square metres can typically be surveyed in one to two days; larger open sites may require several days. The main factors that slow progress are extensive above-ground metallic clutter, steep or waterlogged terrain, and restricted access windows. A clear, stripped site will always yield faster and more reliable results.

The report provides a plan of all anomalies detected, their approximate depth and dimensions, and a priority ranking based on likelihood of being ordnance. It will recommend which targets require supervised excavation. A non-intrusive survey alone does not constitute a clearance certificate; it identifies what may be present and where. Clearance is only confirmed once priority targets have been excavated, assessed, and an ALARP certificate issued.

It can, but performance is significantly affected by existing structures, underground services, reinforced concrete, and metallic debris, all of which create interference that can mask genuine targets. Where a site has already been partially developed, the surveyor will zone the coverage and document any areas where assured detection could not be achieved. For very constrained sites, intrusive CPT methods may be more appropriate.