01 Dec 2017

Assessing the risk

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 risk assessment. It’s exactly the same as a health and safety risk assessment, only the risk comes from another source – potential contamination in the ground, writes Colin Hiscock, Director of Your Environment.


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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 a disproportionate 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 by the planning system.

Each local planning authority has a contaminated land officer who will be able to advise 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 a consent is borne from a mixture of local knowledge and experience of what type of facilities are potentially contaminative. The conditions are phrased differently depending on what local authority you are with. However, they are always in the same vein and normally include three or four separate conditions. These conditions usually take the form of the following stages in the contaminated land assessment process:

Stage 1: Desktop study
Stage 2: Site investigation
Stage 3: Remediation (this includes provision of a remediation strategy normally)
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) – essentially a risk assessment geared primarily to contaminated land, gas and groundwater risks. This model is carried through the whole process right through to stage 4 and is updated at every stage.

This model assesses the risks from potential sources (such as tanks) to potential receptors (for example; small children living in the house) via a pollutant pathway – e.g. ingestion. Let’s say, for example, that there is lead (potentially very toxic) in the ground and you were to grow tomatoes on your site and then someone proceeded to eat these contaminated tomatoes. This would lead to 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 that this link either doesn’t exist or has been removed.

From 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 the 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 additional works required (remediation) or concludes that the pollutant pathway has been broken or doesn’t exist in the first place.

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.

Further information....

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