Assessing Land Contamination
28th November 2020
Land contamination risk management is now a part of most UK developments, particularly those sites with a brownfield legacy. Northpoint outline the various processes of making a land contamination assessment and explain why this needs to be done in a phased way.
Prior to developing a site, you may need to consider several studies and strategies that inform safe design. Preliminary background work is done to ensure your build meets the requirements set out in various British and good-practice industry standards. The process is generally regulated through both planning and building control regimes.
One such consideration of a development is land contamination risk management. In summary, what is land contamination and how is it assessed?
Before you start
Northpoint are routinely contacted by clients requesting assistance relating to land contamination or a land contamination related planning condition.
When a new development is being considered, regulatory authorities often request a Preliminary Risk Assessment or simply set a series of conditions. For land contamination, a number of sub-conditions may be presented. For example:
- Conduct a Preliminary Risk Assessment (Desk Study)
- Conduct a Site Investigation including Conceptual Site Model and Risk Assessment
- Should the investigation find unacceptable levels of contamination, a remediation strategy is required
- Once remediation is completed, a validation report is required to outline how the site has been cleaned-up and is deemed safe
The above is generalised slightly, but is a measure of how the land contamination risk management process needs to be phased commencing with point 1.
The Preliminary Stage
You start to build a picture of the site’s environment. At this stage, you put several pieces of the puzzle together to establish whether features on, in or under the ground may represent a potential risk to a project. This assessment is known as either a Preliminary Risk Assessment or Phase 1 Desk Study stage and targets point 1 of your land contamination condition. The Phase 1 Desk Study should include:
- a thorough site walkover survey
- review of historical maps and records
- an initial assessment of the soils and geology beneath your site (including mining legacy)
- an assessment of environmental search information
- a preliminary geotechnical and geoenvironmental assessment
- the production of a Conceptual Model and Risk Assessment
From the above, a preliminary Conceptual Site Model and Risk Assessment is prepared. Should risks be identified, the desk study is used to design and target a Phase 2 Intrusive Site Investigation. Without the benefit of a desk study, investigation works will not appropriately characterise your site. This may have both cost and time implications for your build as the project progresses.
Getting Your Feet Dirty
At this stage, a good picture of your site will be developed. If investigation is required, you then look to satisfy point 2 above.
Intrusive investigation requirements vary from site to site. Scale and complexity drive overall intrusive design.
At this stage, you are physically conducting works to target any potential concerns highlighted during the desk study phase.
The investigation will normally include:
- Intrusive works, such as boreholes, trial pits and testing to characterise the soils and rocks beneath your site
- Developing a ground model and conceptual representation of whats beneath the ground
- Assessing whether shallow mining activities could impact your build
- Perform both geotechnical and geoenvironmental assessments
It is the geoenvironmental assessment that will consider the land contamination risks. The ground beneath your site, particularly where this has been disturbed through human activity, may include substances that are potentially harmful. These could include materials in soils such as asbestos, heavy metals and oil pollution that may be harmful to public health and groundwater. During fieldworks, various soil and water samples will be retrieved and sent for laboratory analysis. The results are used to establish an actual level of risk. If unacceptable, a clean-up strategy will be required.
Other common contamination assessed during the investigation may include hazardous ground gases and vapours. The assessment will rely on a number of monitoring visits to your site to capture sufficient data to make an appropriate assessment.
Review and Clean-up
From the land contamination risk management process, if you find unacceptable contamination, a clean-up strategy can be developed. At this stage, you are looking to satisfy point 3 in our list.
Again, the remediation strategy can be simple or complex depending on scale and the overall level of risk.
Firstly, we have established areas of contamination and this has been quantified. From this, an Options Appraisal is developed and a measure/s are taken forward within the main clean-up strategy. The strategy will state what needs to be cleaned-up, and how this will be conducted in a way that meet industry standards.
The remediation strategy may consider a number of factors. From simple cut/fill of materials, to use of barriers, clean cover capping systems and ground gas protection measures. In certain circumstances, polluted materials can be chemically or biologically treated. Remediation can be innovative and sophisticated, however one rule of thumb is followed. That is the hierarchy of waste disposal being the least favourable means of remediation. Reuse where possible is always our first priority when developing a strategy.
Once the site has been cleaned-up in accordance with the adopted strategy, we prepare a validation report or completion statement. This will rely on inspection reports, sampling, laboratory verification tests. For larger schemes, materials management will also be considered. Details relating to waste management and the import/export of materials will be documented fully.
Once your site has been cleaned up, you satisfy all of the conditions. At this stage (unless you are considering long-term monitoring), the land contamination risk management process is complete.