21 Nov 2018

The contaminated land assessment process explained

So, you’ve purchased land to build your dream home and the first barrier encountered is a raft of planning conditions or conditions from your warranty company. If the local authority or warranty provider have suspicions of nearby contaminated or infilled land, then they will likely put a standard contaminated land condition on your planning, writes Colin Hiscock, Managing Director of YourEnvironment.

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The contaminated land regime in the UK is set out in a number of documents which outline a framework – or process flow if you like. Much like assessing a risk in health and safety, the overarching theme is a risk assessment. It’s the same as a health and safety risk assessment, just that the risk comes from another source – potential contamination in the ground.

The logical progression for this would be to take a soil sample in every single new-build house to ensure that there is no contamination. However, this would be extremely expensive and not a proportional view to take; bearing in mind that 70% of new development is on greenfield sites. Instead, the process of assessing whether contaminated land will affect your property is dictated through the planning system.

Each local planning authority has a contaminated land officer who will be a consulate on the planning application. These officers are often very experienced and have a vast amount of local knowledge. Therefore, their decision to put a contaminated land planning condition on consent is borne from a mixture of local knowledge and also the experience of what type of facilities are potentially contaminative.

The conditions are differently worded depending on what local authority you are with. However, they are always in the same vein and normally take the form of three or four separate conditions.

These conditions usually comprise the following stages in the contaminated land assessment process:

Stage 1: Desktop study
Stage 2: Site investigation
Stage 3: Remediation (this frequently includes the provision of a remediation strategy)
Stage 4: Validation and verification.

During the whole process, the keystone document is the desktop study. This provides the baseline assumption as to whether the site is contaminated or not. It also provides the geology, historical mapping and other important information.

The key part of the desktop study is the Conceptual Site Model (CSM), primarily a risk assessment geared mainly by contaminated land, gas and groundwater risks. This model is carried through the whole process right through to stage four and is updated at every stage.

This model assesses the risks from potential sources (such as tanks) to potential receptors (small children living in the house, for instance) via a pollutant pathway – for example, ingestion. Let’s say there is lead (potentially very toxic) in the ground and you were to grow tomatoes in the ground and then someone ate the contaminated tomatoes. This would result in a person having lead poisoning. However, if the linkage is broken, then there is no risk. The aim of the staged process is to prove this link either doesn’t exist or has been removed.

In our experience, in most cases; the desktop study is sufficient as we find that no further action is required and the conditions are discharged. However, there are times when a site investigation (SI) is required which can potentially lead to remediation and validation.

A site investigation builds on the information obtained in the desktop study. The whole approach is scientific in nature – the desktop study is a theoretical document that says “we might have contamination here because it used to be a petrol filling station”. The site investigation takes this theory and aims to prove or disprove it.

This is the time where the local authority needs to be involved. It’s important to gain early regulator buy-in. They will provide comment on the desktop study and sometimes require further works to be added to the scope of the SI.

The scope of the SI is dependent on the outcome of the desktop study and can range from simple trial pits with chemical sampling of soils only to installation of boreholes to monitor for gas and groundwater contamination. The results from the SI are then collated into a report (including the data from the desktop study and the initial risk assessment) which builds on the CSM further and provides either an assessment of further works required (remediation) or concludes that the pollutant pathway has been broken or doesn’t exist in the first place.

You may also have a requirement to know what your foundation solution is going to be. Likely, your builder, architect, engineer or warranty provider are looking to get a foundation solution put in place. 90% of the time, we use the same piece of equipment to carry out the geotechnical investigation as we do for the site investigation, as discussed above. Therefore, it makes sense for us to do these at the same time.

Of course, we can carry out a geotechnical investigation on a standalone basis, and we do this every day.

Our aim as a consultant is to guide our clients through this process and provide the liaison between the planners, science, warranty companies and, most importantly, our client. YourEnvironment has many years’ experience in guiding our clients through this process.

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