Land contamination: risk management

Find out the principles of how to manage risks from land contamination if you're a landowner or developer.

You should carry out risk management so you can estimate how likely and serious any contamination is, make decisions about how to manage it and then carry out the work.

You should use this guidance as an introduction to how to:

  • use risk assessments to consider dangers contamination might cause
  • find the best solutions to manage contamination and make the most of the money and time available
  • prevent or manage contamination by developing and implementing a plan based on the results of risk assessments
  • check that any prevention or management of contamination is being done correctly and legally and will work

Read the Model procedures for the management of land contamination (CLR11) for further information.

Who should use this guidance

You should use this guidance if you’re:

  • developing land, including getting planning permission
  • preventing or managing contamination on your land voluntarily
  • preventing or managing contamination because you have to by law
  • making decisions about potential problems on one or more sites on behalf of someone else

You’ll need help from experts or specialist consultants who are suitably qualified and competent. They’ll normally be chartered members of an appropriate professional body who can show that they have relevant knowledge and experience. An example of a relevant qualification is the Specialist in Land Condition (SiLC).

Manage contamination by assessing risks

Assessing risks means you can estimate what might happen and how bad it would be, and use this knowledge to help make decisions. You must reduce uncertainties where you can and clearly explain the ones that remain.

You may find it difficult to get exact measurements of contamination, know how widespread it is and predict what harm it may cause for reasons including:

  • a lack of scientific information about how substances in the soil behave
  • contaminant levels often vary with depth, and from one spot to the next
  • the possible effects of contamination vary in different circumstances, eg depending on how any land is used or what else is in the soil
  • the difficulty of predicting when and how substances might cause harm to people or animals or pollution of water, or might react with other substances in the soil to cause these effects, because every person and situation is different

Carry out risk assessments

You must always start with a preliminary risk assessment to:

  • define the objectives of the assessment
  • collect basic information about the site and any contamination risks
  • decide if any further assessments are needed

You may then have to use one or both of the following risk assessments to estimate how serious contamination is.

  • a generic quantitative risk assessment - to collect more site information for comparison with general standards, also known as generic assessment criteria (GAC), to decide if the level of risk needs more detailed assessment or a plan for dealing with the contamination
  • a detailed quantitative risk assessment - to collect more site information for comparison with bespoke standards, also known as site specific assessment criteria (SSAC), so you can decide if you need to create a plan to deal with any contamination

Risk assessments get increasingly complex, involve more data and are likely to take more time as you move from preliminary to generic to detailed risk assessments. Each stage builds on the information discovered in the previous stage.

Risk assessment report

At each stage of risk assessment you should produce a report that explains how the assessment was carried out. The report should describe what assumptions were made and find one of the following conclusions:

  • nothing needs to be done about the contamination based on your assessment
  • you have enough information to take action to deal with unacceptable contamination – if this happens you should proceed to a review of the best way to take action (known as an ‘options appraisal’)
  • there isn’t enough information to decide what should happen next - if this happens you should carry out further assessment, at the next level of complexity where necessary, eg if a generic quantitative risk assessment was inconclusive you should do a detailed quantitative risk assessment

How to carry out a preliminary risk assessment

A preliminary risk assessment includes the following steps:

  • decide what your assessment aims are, eg reducing the risk of possible harm in the future or cleaning up contamination that’s already happened
  • get information about the site
  • get information about the contamination
  • use the information you’ve got about the site and the contamination to study the risks and estimate how likely and harmful the risks are
  • decide what, if anything, should be done next, eg more detailed assessments
  • create a rough outline of the situation (known as a ‘conceptual model’), eg a diagram that includes the most important information about the land, the contamination, what it can harm and how

After you’ve completed your preliminary risk assessment, you should write a report that summarises the information you’ve found. You can use the report to describe your preliminary conceptual model for the site.

How to carry out a generic quantitative risk assessment

Carry out a generic quantitative risk assessment to get a more detailed understanding of the site and the contamination so you can decide what to do next. The assessment will:

  • use generic assessment criteria and assumptions to study the links between the sources, pathways and receptors
  • improve your conceptual model of the site
  • help you decide what further action you must take

You should collect information using a combination of:

  • one or more site investigations
  • a review and analysis of detailed information about the site (desk research)

You should write a report that summarises what information you’ve found from doing the generic quantitative risk assessment, including:

  • your conclusions
  • how you’ve refined your conceptual model
  • any uncertainties
  • what you’re going to do next

How to carry out a detailed quantitative risk assessment

If you’ve done a preliminary risk assessment and potentially a generic quantitative risk assessment and you still don’t have enough information to make decisions then you should do a detailed quantitative risk assessment.

The detailed quantitative risk assessment should proceed in a similar way to a generic quantitative risk assessment, but will be more detailed and include more site-specific data and criteria, often discovered by more thorough site investigations.

You should write a report that records how you have completed the detailed quantitative risk assessment, how you’ve refined your conceptual model and your conclusions. Include in your report:

  • information about the standards used to estimate risks and make decisions
  • any assumptions made
  • details of any uncertainties
  • what you’re going to do next

Manage contamination

Deciding how to manage the problem is called an ‘options appraisal’. Managing the problem, sometimes involving preventing or cleaning up contamination, is known as remediation.

How you choose to remediate contamination will usually involve identifying possible options, assessing them in depth and then deciding on your approach. Relevant factors include:

  • if one or any combination of solutions can be used on the site, eg because of where the site is, how big it is and how easy it is access
  • if there’s any way to prove the chosen solution or solutions will work, eg because it’s been proven to prevent or reduce contamination in similar situations elsewhere
  • how long it will take for the solutions to reduce or prevent harmful contamination
  • how much it’ll cost
  • if the solution or solutions will get the approval of everyone with an interest in the land
  • getting all the legal permissions and approvals needed to do the work - what you need will vary depending on the site and the contamination
  • how long the solution will work for and if that suits what the site’s being used for or is going to be used for

Write a report that summarises the solutions you’ve chosen and why - this is your ‘remediation strategy’.

Create a detailed plan and do remediation

After you’ve done the risk assessments and options appraisal, you should create a plan explaining how remediation is going to be carried out (known as an ‘implementation plan’).

Prepare the implementation plan by talking to people with an interest in the land and the regulators. It will be based on and explain how to implement the remediation strategy. You should agree the plan with people with an interest in the land and any regulators.

Carrying out remediation involves designing in detail how it will be done, and then doing it in a safe and effective way. It includes doing trials if needed, getting any permits or approvals and doing the remediation with appropriate supervision and checks.

Check and monitor remediation

After and sometimes during remediation the work should be checked to see if it’s being or has been done correctly. This is called ‘verification’. A verification plan should be produced during the design stage, saying how this will be checked, when and by whom. A verification report should then be produced.

A plan should be produced saying what longer term monitoring or maintenance should be done, if needed. Monitoring and maintenance should be kept under review - any changes should be approved by the regulator.

You must keep records explaining what was done, what happened and what decisions were taken. Reports should be written to record progress and on completion, showing that the monitoring and maintenance goals have been met.

Published 7 April 2016