Initial UXO Survey

Our work on this site started with a Non-Intrusive UXO Survey using our advanced push-cart system. This method involved a two-person team manually pushing our surveying equipment across the designated area. The five-channel system, equipped with sensors, can detect ferromagnetic anomalies beneath the surface through magnetometry. This approach allows us to survey to an assured depth of 4 metres, with slightly greater depths achievable for larger ordnance.

Data Processing and Analysis

Post-survey, the collected data was processed by our geophysics team at Brimstone’s Head Office. The data underwent several refinement steps to enhance quality and reduce noise. Our technical team then used a specialist computer model to compare the survey data against a bank of known UXO signals.

The result of this processing was a range of targets that were identified as requiring further investigation due to their resemblance to unexploded ordnance. Using our bespoke software, our team was also able to make estimations of the depth and mass of the items, along with their location in coordinates accurate to 5 centimetres.

The particular target that resulted in the mortar being found was number 336. Below you can see the signal this target produced and how it appeared on the false colour map.

Target Investigation and UXO Discovery

With the data indicating that there could be items of ordnance beneath the surface, we liaised with our client to ensure that no ground intrusion works started before we investigated further. We then deployed our engineering team back to the site to carry out a UXO Target Investigation.

A Target Investigation is where our engineers use a GPS system to pinpoint the targets on site, using the coordinates provided by our technical team. They then use hand tools to carefully unearth the targets, leaning on the resources of excavators for significantly deeper targets.

As mentioned previously, upon investigating target 336, our team unearthed a 3” ML Mortar.

The 3” ML Mortar was a common anti-personnel weapon used in WWII by the British Army, with an estimated 6.5 million high explosive ML mortars produced in 1942 alone.

Weighing around 4.5kg, these pear-shaped items had a brown body with a five-finned green tail. Several variants of the item were produced, including smoke, white phosphorous, inert practice, and parachute illumination variations.

Ensuring Safe Disposal

After the mortar was unearthed, our engineers consulted with local authorities and the Army to arrange its safe disposal. A military EOD unit was deployed to the site, who disposed of the item on the same day. This collaboration ensured minimal downtime for our client, preventing costly delays and maintaining safety.

While Brimstone has the licenses and capability to dispose of UXO, we often leverage British military resources to minimise costs for our clients. In this case, the Army’s involvement exemplified this approach.

With all targets investigated and the mortar safely disposed of, we de-mobilised from the site and provided our client with a UXO ALARP (As Low As Reasonably Practicable) certificate. This certification assured our client that the risk of UXO had been mitigated, allowing them to proceed with their planned ground intrusion activities safely.