Risk Assessment Findings

Initial research through a Preliminary UXO Risk Assessment identified the location as potentially impacted by wartime activity. A subsequent Detailed UXO Risk Assessment confirmed this concern, uncovering twelve recorded air raid incidents within 1km of the site and fourteen high explosive bomb strikes within approximately 300 metres. One of these was recorded within the site boundary itself.

Aerial imagery from 1942 further supported these findings, showing visible ground disturbances across the site, including a crater-like feature in the northern section. Although parts of the land were likely accessed during the war, much of the area, particularly the open fields and orchard, would have been visited infrequently. This increased the likelihood that any unexploded bombs could have gone unnoticed and remained undisturbed. There was also a further probability of unobserved bomb strikes on the site due to many of the air raids in the immediate vicinity taking place in the hours of darkness.

Given the confirmed nearby bomb strikes, signs of surface disruption, and limited wartime access, the risk of encountering UXO was assessed as Moderate.

The likelihood of Allied unexploded anti-aircraft ammunition was also considered in the risk assessment due to frequent Luftwaffe activity and the presence of several HAA batteries within range of the site. However, the absence of evidence for on-site military activity meant the risk from legacy military use was considered Low.

Survey Strategy and Risk Mitigation

In accordance with industry guidance, a moderate UXO risk is deemed as intolerable. Therefore to reduce this risk to a level that would allow the development to proceed safely, Brimstone proposed a multi-phase mitigation strategy.

The first step was a UAV Magnetometry Survey, designed to quickly and efficiently scan the site for magnetic anomalies consistent with buried ordnance. The survey initially identified 105 targets. After further modelling and assessment, this list was refined to 85 priority targets requiring further investigation. In May 2024, Brimstone returned to the site to carry out a Target Investigation for these anomalies. Thankfully none of these targets turned out to be items of ordnance.

The next stage of UXO risk mitigation was an Intrusive UXO Survey. Over the course of five separate visits, Brimstone’s engineers conducted 981 probes across the site using an advanced CPT Rig. These surveys were carefully planned to align with Jenner’s construction timeline and ensured that all piling and groundwork operations could proceed with confidence. The team’s ability to return as needed demonstrated flexibility and a clear commitment to supporting progress on site.

Outcome

No unexploded ordnance was encountered during any stage of the investigations. Upon completion of the survey work, Brimstone issued an ALARP (As Low As Reasonably Practicable) certificate, confirming that UXO risk had been reduced to a level that no longer required mitigation.

Supporting New Build Projects

This project demonstrates Brimstone’s ability to deliver full-spectrum UXO risk mitigation on complex residential developments. By combining rigorous historical research, advanced UAV survey technology, and over 900 intrusive probes, we ensured Jenner could move forward with the Seasalter development safely and without delay. Our collaborative, flexible approach was key to maintaining momentum across multiple site visits – delivering assurance where it mattered most.

Planning a residential or infrastructure project on previously undeveloped land? Get in touch with Brimstone UXO to discuss how we can support you from initial risk assessment through to final sign-off.

Contact us today at enquire@brimstoneuxo.com or call 0207 117 2492 to speak with our team.