Guidance

Supporting minimising environmental impacts from unexploded ordnance clearance

Published 21 January 2025

1. Introduction

The UK government and devolved governments have national and international obligations relating to the management of our seas and the protection of habitats and species. We are committed to taking the necessary measures to achieve and maintain good environmental status of our waters through the UK Marine Strategy. 

We recognise the impacts clearance of unexploded ordnance (UXO) can have on our marine environment. After both World Wars, large numbers of explosives were left undetonated in the marine environment. An increase in marine development is leading to the discovery of a great number of UXOs, which need to be cleared to protect human life and infrastructure. 

Clearance has previously been undertaken by placing explosive donor charges next to the UXO. When this donor is detonated, it causes the UXO to detonate through a process referred to as high order detonation. This blast can produce high levels of energy which can result in considerable impacts on the marine environment. These impacts can include seabed damage, and injury and disturbance to marine species from the associated noise. 

There are low noise alternatives to high order detonation that are safe, commercially available and cause less environmental harm. Those currently available still require the use of a donor charge to carry out clearance (although this charge is much smaller than those typically used for high order clearance), but they render the UXO safe without resulting in a high order detonation. As less energy is emitted into the marine environment, the potential for environmental impacts is lower than for high order clearance.

A marine licence is required for UXO clearance activities. When applying for marine licences, the Joint Position Statement sets out that low noise methods should be the default method of clearance. If there are extraordinary circumstances which mean low noise clearance cannot be undertaken, applicants should engage with the appropriate licensing authority and statutory nature conservation bodies (SNCBs) at the earliest opportunity.

Extraordinary circumstances are those in which high order clearance is the only viable option and it is clear that low noise methods cannot be attempted. Such circumstances might include those where the factors of the UXO or of its location (such as depth, level of degradation or shell thickness) far exceed the expected or demonstrated capabilities of any known low noise clearance tools such that any attempt to use low noise tools would not be feasible.

The Joint Position Statement represents the collective view of the following:

• Department for Environment, Food and Rural Affairs (Defra)
• Department for Energy Security and Net Zero
• Marine Management Organisation
• Scottish Government
• Welsh Government
• Natural Resources Wales
• NatureScot
• Department of Agriculture, Environment and Rural Affairs (DAERA)
• Joint Nature Conservation Committee
• Natural England

This guidance has been produced by Defra, in collaboration with signatories to the Joint Position Statement, to provide more information to support UXO clearances. It should therefore be read in conjunction with the statement. Please note that this guidance is applicable in English, Welsh and Northern Irish waters only. For Scottish waters, please see Marine licensing: overview and Marine environment: licensing and consenting requirements.

This guidance sets out how the signatories expect applicants to approach marine licensing for activities relating to UXO clearance and provides guidance to potential applicants as to how best to undertake applications for such licences, in the context of this general approach. This guidance is not exhaustive; however, for the avoidance of doubt, it should be noted that applicants are expected to have ensured that there are no barriers, legal or otherwise, to their UXO operations. Following this guidance does not absolve a licence holder from obtaining such authorisations and consents that may be required under any other legislation.

It remains the case that any and all applications for marine licences will be determined on a case-by-case basis, on the basis of the application that has been made and the individual circumstances. The approach the signatories generally expect to take with regards to marine licensing for UXO clearance, as set out in this document, is in no way to be taken as the signatories pre-determining whether or not a marine licence will be granted or pre-determining what conditions will be applied to such marine licences.

2. Your marine licence application

Under UK legislation, it is an offence to carry out (or cause or permit to carry out) certain marine activities without a marine licence or in contravention of any marine licence conditions. Section 66 of the Marine and Coastal Access Act 2009 (MCAA) and Section 21 of the Marine (Scotland) Act 2010 (MSA) contain a list of the activities that may only be undertaken in the marine environment under a marine licence. This includes: 

• depositing or using any explosive substance or article within the UK/Scottish marine area either in the sea or on or under the seabed; and
• incinerating any substance or object on any vehicle, vessel, marine structure or floating container in the UK/Scottish marine area

In addition, a marine licence is also required when:

• using a vehicle, vessel, aircraft, marine structure or floating container to remove any substance or object from the seabed within the UK/Scottish marine licensing area
• carrying out any form of dredging within the UK marine licensing area (whether or not involving the removal of any material from the sea or seabed)

As a result, marine licences are required for UXO clearance and may be required for investigative surveys to confirm the presence of UXOs.

The marine licensing processes are set out in Parts 4 of the MCAA and MSA. The additional guidance in this document is provided for those applying for marine licences to clear UXO in English, Welsh and Northern Irish waters. Further guidance is provided by each licensing authority about their marine licence application processes: 

• Marine Management Organisation – marine licensing in all English waters, and Northern Irish offshore waters
• Marine Directorate – marine licensing in Scottish waters
• Natural Resources Wales – marine licensing in Welsh waters
• DAERA Marine and Fisheries Division – marine licensing in Northern Irish inshore waters
• Offshore Petroleum Regulator for Environment & Decommissioning (OPRED) – marine licensing in UK waters for the oil and gas; carbon capture, utilisation and storage; and gas storage industries

All marine licence applications will be considered by the appropriate licensing authority on a case-by-case basis. 

Marine licence applications should enable licensing authorities to understand how proposed activities will affect the marine environment, including protected sites and species. The applicant should therefore include an assessment of environmental impacts and any other information required by the licensing authority, including information to support the additional assessments required if operations are within, or have the potential to affect, a Marine Protected Area (MPA). Failure to provide sufficient information can result in delays in the consenting process and may result in the application being rejected. Marine licences may include conditions requiring mitigation and monitoring.

2.1. What needs to be cleared?

Marine licence applications should provide a total number of UXOs to be cleared. This should be as accurate as possible. Ideally, the location and type of each UXO should also be provided. This will enable licensing authorities to best assess the application and the need for any marine licence conditions. 

If providing this level of detail is not possible (for example, investigative works of potential UXOs have not yet been undertaken or have not been successful), a summary of the types of UXO that may be encountered should be included in the application, with the likelihood of finding each type listed. This information can be obtained from the desk-based risk assessment; including a copy of this report as an annex can be beneficial but is not essential. 

Investigation of potential UXOs may also require a marine licence. A 2-licence approach is strongly encouraged in such circumstances, where one marine licence is obtained for investigative surveying and a second for clearance, to enable a more accurate description of required clearance activities in the second marine licence.

An explanation of how the number of clearances requested in the marine licence application was determined should also be included, with an overview of any surveys undertaken to inform this (for example, geophysical and magnetometer surveys to identify potential UXOs).

2.2. Proposed clearance tools

Low noise methods of clearance should be the default method used to clear any type of UXO in the marine environment.

The following information should be included in an application:

• the brand of clearance tool to be used
• the operator which will conduct the clearance
• a detailed methodology for deploying the chosen clearance tool
• how much explosive material the clearance tool will contain (TNT equivalent weight)

If multiple types of UXO are required or expected to be cleared, the application should highlight:

• if the type or size of clearance tool may vary with UXO type
• if multiple attempts to clear all the explosive material may be required due to the volume of explosive material contained
• if multiple attempts may be required for other reasons (such as for exploratory reasons or due to extensive marine growth on the UXO casing)

Details of planned post-clearance surveys to ensure no residual material has been left should also be included in the application, including:

• the size of area to be surveyed
• the minimum size to be collected
• how residual material will be collected and disposed of (if appropriate)

It is recommended that residual material is collected as soon as possible post-clearance to minimise risk of chemical contamination to the surrounding water column – this should be reflected in the application. 

Robust evidence demonstrating the level of noise reduction expected for the chosen clearance tool should also be provided in the application. This information will be important when assessing environmental impacts, the outputs of which will determine the level of mitigation and monitoring required. Robust evidence in this instance means data and information that clearly demonstrates the effectiveness of the proposed clearance tool in reducing levels of noise emitted into the marine environment compared to an equivalent high-order clearance (for example, results from controlled experiments).

Further information on how this evidence should be collected can be found in Section 5.

2.3. Informing environmental assessment

Marine licence applications relating to UXO clearance are expected to include an assessment of environmental impacts, which usually includes noise propagation modelling. To complete this, the level of noise expected to be produced by the detonation, referred to as the source level, is needed. The outputs of this assessment are important when identifying the level of environmental risk from the proposed detonation and determining what mitigation and monitoring is required. 

Low noise tools that initiate a deflagration process aim to clear UXOs without the explosive material within detonating. For the purpose of environmental assessment, if it can be reliably assumed that the noise produced will be from the deflagration tool only (this may be referred to as the donor charge), this should be reflected in any noise modelling undertaken to support the application.

If a marine licence application includes high order clearance, either in extraordinary circumstances or as a contingency, as a minimum, noise modelling should be undertaken for the device with the largest volume of explosive material. However, it is recommended that multiple scenarios are assessed to reflect the range of devices and corresponding explosive weights that are expected to be present. This noise modelling must consider the TNT equivalent weight of the UXO plus the expected donor charge.

2.4. Contingency high order clearance

It is not acceptable to expect a high order contingency for every confirmed UXO required to be cleared during a clearance campaign. High order clearance methods should always be the last resort.

If high order clearance is to be included as a contingency in the event a low noise method fails, the number of contingencies acceptable should be discussed with the appropriate licensing authority and SNCBs, ideally prior to submitting the marine licence application. This will enable an appropriate number to be proposed that considers the location and timing of the campaign, and the UXOs that require clearing.

Applicants should demonstrate in the application what measures will be applied to ensure high order clearances will be avoided as far as possible. This contingency should only be applied to a UXO where the following conditions are met:

1. The most appropriate low noise method has failed after a minimum of 3 attempts.
2. All best practice has been demonstrably applied.
3. There is prior agreement with the appropriate licensing authority.

Applicants should also consider whether a potential UXO could be a training device with no explosive charge, which would not require high order clearance.

If a contingency high order detonation occurs, evidence should be provided in any post-clearance report, demonstrating and explaining:

• that the low noise method was attempted
• how many times it was attempted with details of what investigations were undertaken between each attempt to ascertain why it failed
• what changes were made to get the low noise method to work in the following attempt

3. Mitigation and monitoring

3.1. Mitigation of impacts

Regardless of the clearance tool or method used, all applicants should avoid, reduce and mitigate environmental impacts as far as possible.

The marine licence application should be supported by a mitigation plan which will reduce potential environmental impacts as far as possible. Mitigation proposed by the applicant will be considered by the licensing authority with advice from SNCBs, to ensure the proposed measures are sufficient. This review will include the clearance method proposed, the evidence supplied to demonstrate the effectiveness of the chosen clearance tools and the potential environmental impacts of the clearance. Mitigation plans should be agreed with the licensing authority. Compliance with any agreed mitigation plan may be conditioned in any marine licence issued.

3.1.1. Injury to marine mammals

Cetaceans (all species of dolphin, porpoise and whale) and seals are protected under UK law. There are various offences which relate to capturing, injuring, killing or disturbing wild cetaceans and seals. Relevant legislation includes:

• The Conservation of Habitats and Species Regulations 2017
• The Conservation of Offshore Marine Habitats and Species Regulations 2017
• The Conservation (Natural Habitats, &c.) Regulations 1994
• The Conservation (Natural Habitats, etc.) Regulations (Northern Ireland) 1995
• The Conservation of Seals Act 1970
• The Marine (Scotland) Act 2010
• The Wildlife (Northern Ireland) Order 1985

It is therefore anticipated that a mitigation plan to reduce impacts to marine mammals will be required. Applicants should consider their responsibilities under other legislation, including but not limited to those regimes set out above.

When drafting a mitigation plan, JNCC mitigation guidelines for clearing UXO should be followed. These guidelines set out the minimum mitigation requirements for marine mammals and can be adapted to the specifics of the project concerned.

If the number of UXO that may need clearing is unknown, assessing multiple scenarios in the environmental assessment can support a tiered approach to mitigation based on the type of UXO being cleared at a particular time.

If high order clearance is included in the work scope, either in extraordinary circumstances or as a contingency, the maximum mitigation available should be included in the mitigation plan for these clearances. 

The JNCC guidelines focus on mitigation for marine mammals - in particular, cetaceans. In some areas there may be a requirement to mitigate noise impacts on other species such as fish, diving birds or turtles. In such cases, the appropriate licensing authority and SNCBs should be consulted prior to submitting the application.

3.1.2. Seabed disturbance and impacts to benthic species

If UXO clearance is required close to sensitive benthic or seabed features, mitigation options to reduce impacts to these should be included in the mitigation plan.

Methods to mitigate impacts to these features should always be considered whenever high order clearance is included in a marine licence application, either in extraordinary circumstances or as a contingency. It is currently presumed that low noise methods of clearance will result in less seabed damage than high order clearance due to the lower energy levels produced by these methods. JNCC is currently considering guidance regarding impacts from UXO clearance to benthic features. In the meantime, the following should be explained in an application:

1. How far is the device from the feature concerned, what size of crater could occur because of the detonation and what is the risk and extent of potential damage to the features concerned?
2. Is moving the UXO to another location away from the sensitive feature prior to clearance a viable option (lift and shift)? This assessment should be made by the Explosive Ordnance Disposal (EOD) experts undertaking the investigative survey, who will determine if the device is stable enough to move safely. Where to move the device to, should be discussed with the appropriate licensing authority and SNCBs. If the device is to be cleared at the new location, a low noise method of clearance should be attempted first, as outlined in Section 2.4.

Please note that any marine licence issued may require the licence holder to undertake a post-clearance assessment of impacts. This may include long-term monitoring to ensure recovery of the seabed. Requirements for this will be determined by the licensing authority but including what such monitoring could involve in the mitigation plan will facilitate discussions.

3.1.3. Chemical contamination

Concerns have been raised about chemical leaching from explosive compounds in munitions left in the marine environment (for example, Maser (2023), Lepper (2024)). Both high order and low noise methods of clearance aim to remove all explosive material within a UXO and so not leave any material that can release contaminants.

However, 2 areas of concern have been raised regarding chemical contamination from deflagration:

• chemical leakage from explosive material not fully burned and left on the seabed
• release of chemicals during the burn process

Further research on potential contamination from deflagration will provide greater clarity on what may be released during the deflagration burn process, but recovery of debris left on the sea floor following clearance will mitigate the risk of contamination from any residual material. Removal of residual material from the seafloor should be considered best practice, regardless of the clearance method used. 

Details should be provided in the mitigation plan regarding the following:

• options for the collection and disposal of debris
• the size of area that will be searched for debris (radius around the device)
• the minimum size of debris that will be collected and how it will be disposed of

The plan should also provide details of how the recovery will be undertaken - for example, using a Remotely Operated Vehicle (ROV) - and whether it requires a container to collect debris into and if so, where will this be located.

3.2. Noise monitoring

Marine licence holders are encouraged to undertake noise monitoring, regardless of whether it is a consent requirement, to:

• expand the knowledge base on potential impacts
• support the use of tools which reduce impacts

Marine licence holders may be required, as a marine licence condition, to undertake noise monitoring during clearance activities to:

• verify conclusions drawn in the environmental assessment
• support claims a particular method or tool will result in lower noise levels compared to high order detonation

The need for noise monitoring will be considered on a case-by-case basis at the application stage. 

Noise monitoring should comply with the protocol provided by the National Physical Laboratory for in-situ underwater measurements. Additional or more detailed requirements may be stipulated by the licensing authority during the application process and included as a consent condition.

Once the clearance campaign is complete and results have been submitted to the licensing authority for review, they may be made publicly available. Defra is currently investigating how best to make monitoring data more accessible. When this is complete, further guidance will be provided.

3.3. Expectations for mitigation and monitoring

Whilst all UXO clearance applications will continue to be considered on a case-by-case basis by the appropriate licensing authority, further guidance is provided in this section on how different clearance tools might be considered in applications and what associated mitigation and monitoring requirements could be expected. 

It outlines how licensing authorities and SNCBs might choose to treat applications and sets out a hierarchy of preference where Category A is preferred and should be aimed for by all applicants. It recognises that different clearance tools are in different stages of development with varied levels of supporting evidence, and that high order detonation may still be needed where there are extraordinary circumstances which mean low noise clearance cannot be undertaken.

The hierarchy assumes clearance via either low-noise or high-order detonation techniques is required and that other options such as lift and shift or micro-siting of infrastructure to avoid UXOs, have been ruled out.

It considers the risks associated with noise from UXO clearance (such as injury and disturbance) and the evidence available to support the use of different tools. It is based on the primary method of clearance proposed. Any contingency usage of high order clearance is considered separately and should be discussed with the appropriate licensing authority and SNCBs.

Hierarchy of preference

Category A (preferred)

Proposed clearance:

Clearance using a low noise tool proposed; robust evidence is available from both controlled testing and at-sea clearances to support claims this method will result in reduced environmental impacts compared to high order clearance. 

Expected mitigation and monitoring:

This category is anticipated to have the lowest environmental impact and therefore the lowest mitigation requirements. There should be sufficient information to support the specified tool as being within this category, providing confidence in the level of noise reduction predicted. In such a case, additional noise monitoring may not be needed. As a minimum, applicants should expect a pre-clearance search using marine mammal observers to be required.

Category B

Proposed clearance:

Clearance using a low noise tool proposed; robust evidence is available from controlled testing to support claims this method will result in reduced environmental impacts, but no or limited at-sea data available. 

Expected mitigation and monitoring:

Tools in this category will have evidence from controlled testing providing confidence that noise levels will be reduced compared to high order clearances, which is robust enough to facilitate use of the specified tool at sea. As a minimum, applicants should expect a pre-clearance search using a marine mammal observer to be required, possibly supplemented with an Acoustic Deterrent Device (ADD).

Provided the controlled evidence is robust and the noise assessment predicts injury will not occur within ranges that can be mitigated using an ADD, noise abatement may not be required. Noise monitoring may be required to demonstrate that results obtained in the controlled testing transpose to in the field. Once sufficient evidence at sea is available, tools in this category may be able to progress to category A.

Category C

Proposed clearance:

Clearance using high-order detonation proposed under extraordinary circumstances; clear justification as to why this is the only option. 

Expected mitigation and monitoring:

There may be extraordinary circumstances in which high order clearance is the only viable option and it is clear that low noise methods cannot be attempted. Such circumstances might include those where the factors of the UXO or of its location (for example, depth, level of degradation or shell thickness) far exceed the expected or demonstrated capabilities of any known low noise clearance tools such that any attempt to use such low-noise tools would not be feasible.

The licence application should include a clear explanation as to why low noise methods cannot be attempted. Applicants should expect the maximum mitigation, including noise abatement, to be required. A European Protected Species licence to injure may also be required.

Category D (avoid)

Proposed clearance:

Clearance using high-order detonation proposed; insufficient justification as to why this is the only option proposed.

Expectation:

This application may be rejected pending further information.

Licensing authorities may take a different approach depending on the specifics of the application being reviewed. For example, due to the location (including if in or near an MPA), the type and size of device requiring clearance or the results of the environmental assessment. Early engagement with the appropriate licensing authority and SNCBs is recommended to provide greater certainty on what will be required by individual projects and allow a smooth review process.

The following are a series of questions to support the applicant in determining which category their application best fits into.

Question 1.

What method of clearance is proposed?

• if high order detonation proposed, go to question 2
• If low noise method proposed, got to question 3

Question 2.

Are there extraordinary circumstances in which high order detonation is the only viable option?

• yes: expect highest level of mitigation to be required (Category C)
• no: expect application to be rejected (Category D)

Question 3.

Is evidence from controlled testing provided? Does this demonstrate that the chosen clearance tool is effective?

• yes: go to question 4
• no: do not proceed. Only tools with evidence showing their effectiveness during controlled testing should be used at sea

Question 4.

Is evidence from at-sea testing provided? Does this demonstrate that the chosen clearance tool is effective?

• yes: expect a low level of mitigation to be required (Category A)
• no: expect additional mitigation to be required (Category B)

Go to question 5

Question 5.

Does the application include contingency usage of high order detonation?

• yes: discuss with the appropriate regulator and SNCBs. Expect only a restricted number of contingencies to be agreed
• no: proceed with application

4. Reporting

4.1. Post-clearance reporting

Marine licence conditions may include a requirement to submit a report to the licensing authority detailing the outcomes of the clearance activity (returns). The details of such a report will be case-specific, but it is recommended that it should include:

• an overarching summary of the clearance works undertaken, methods used, and any problems encountered, supplemented with annexes
• an overview of all mitigation employed, whether actions were required and discussion/description regarding its effectiveness. This section can replace the need for a separate MMO mitigation report; however, it should usually include all the information typically included in that report. Guidance on what to include in this section can be found in the JNCC mitigation guidelines
• conclusions from noise monitoring (if applicable)

It is recommended that the following should be supplied as annexes: 

• a detailed noise monitoring report
• a completed JNCC marine mammal mitigation spreadsheet
• target investigation reports (TIRs)

Note: when providing the standardised spreadsheets used for marine mammal mitigation, these should be submitted in their original Excel format and not as a PDF. In addition to providing evidence that mitigation was undertaken as required, this data may be collated by JNCC who may use it to inform future updates to their mitigation guidelines.

4.2. Marine Noise Registry

Marine licences may have a condition that data be submitted to the Marine Noise Registry (MNR) detailing all clearance activities undertaken. Note that the MNR requires predicted and post-clearance data to be submitted.

5. Robust supporting evidence for low noise methods of UXO clearance

All marine licence applications should include a detailed account of the proposed tool for clearance, ideally for each UXO identified, and use this to identify realistic scenarios for the environmental assessment accompanying the application.

To date, deflagration is the main low noise alternative to high order clearance. This section of guidance is written with that method in mind and will be updated should alternative low noise methods become more widely available in the future.

Some of the deflagration tools currently available have been developed for use in a military context but not previously used commercially, while others have been used on commercial projects – see Ocean Winds 2024 for a commercial-scale example.

The level of evidence supporting claims of reduced noise levels may vary between tools, and there is currently insufficient evidence to assume all deflagration tools will produce the same level of noise. As a result, marine licence applications should include robust evidence demonstrating the level of noise expected for the clearance tool proposed. Failure to provide this evidence can result in delays in the consenting process and if licensed, a requirement for more robust mitigation or monitoring.

An aim of this part of the guidance is to encourage comparisons between tools and facilitate consistency in mitigation and monitoring requirements.

This guidance recommends a 2-tier approach to obtaining evidence of reduced noise levels:

5.1. Experimental testing in a controlled environment

Experimental testing in a controlled environment is the preferred first stage. This is because it provides greater certainty that observed noise reductions in the water column are due to the tool being used. For example, by reducing doubt that lower noise levels are due to other factors such as sound being absorbed by underlying sediment.

A controlled environment refers to an environment with specific controllable parameters. In this case, the volume of viable explosive material is known and controlled. Using a safe, controlled environment (such as a flooded inland quarry) will also ensure initial noise measurement data are collected without risk to the marine environment. These controlled tests should not be undertaken at sea.

This is the minimum level of evidence that should be provided when applying to use a low noise tool with reduced mitigation requirements compared to high order clearance, as outlined in the hierarchy of preference.

Defra is supporting a final phase of controlled trials of suitable technologies in 2024. Beyond this, we expect evidence from controlled testing to be acquired independently.  We encourage the results from such testing to be made publicly available so it can be referenced in marine licence applications. An example of how this kind of data can be collected is the controlled experiment undertaken by Robinson (2020), who demonstrated that a low order deflagration tool achieved a 20 dB re 1µPa reduction in noise compared with an equivalent high order detonation.

5.2. Noise data from at-sea clearances

At-sea noise monitoring may be required, and should be regarded as best practice, during UXO clearance campaigns. Marine licence applications which propose the use of new clearance methods or tools at sea should meet the following criteria:

• there is robust evidence of noise reduction in a controlled environment
• sufficient evidence is provided within the application to ensure appropriate mitigation can be undertaken
• noise monitoring is undertaken during the clearance activities
• the methodology is sufficiently detailed for others to be able to use

Noise monitoring should be compliant with protocols provided in the National Physical Laboratory Protocol for in-situ underwater measurement of explosive ordnance disposal for UXO (2020). An example of a clearance campaign using a low noise method where noise monitoring was undertaken can be accessed on the Ocean Winds website. Additional or more detailed requirements may be stipulated by the licensing authority during the application process and included as a consent condition.

The level of data required may vary for different tools and will consider the quality and quantity of data available. The level of data that is considered sufficient will be determined by the licensing authority with advice from their SNCBs.