Dealing with contaminated land planning conditions

by Dr. Richard Wesson
(Bristol)

What is contaminated land?



Contaminated land can be broadly defined as land that has substances present in, on or under the ground that have the potential to be hazardous to health or the wider environment. However, the presence of contamination does not necessarily mean that the land will be classed as contaminated. What is critical is whether it has the potential to be hazardous to health or the wider environment of which more later.

How does this affect me?


If you are developing a site on land that has been previously used i.e. brownfield land the planning permission may be granted, but with a condition attached requiring you to investigate and potentially remediate the land.

What do planners require?


The planners will normally place a standard condition on the planning permission that will state no development can take place until an investigation and risk assessment to assess the nature and extent of any contamination on the site has taken place. This will normally also state that a remediation a scheme should be submitted to deal with any contamination. This can sound pretty intimidating if you have never encountered one before. However, it is important to bear in mind that this is a standard condition that they will put on any planning permission where they suspect contamination. The site investigation is the key and should follow a risk based approach – remediation (i.e. clean up) of the site is only required if risk assessments should that there is a significant possibility of significant harm likely. Site investigations should be carried out in phases, with each stage following on from the next. As part of this process, the condition may also require what is described as a ‘conceptual model’ of which more in the next section.

What does a site investigation involve?


As we have discussed, a site investigation should be carried out in stages. The first stage is a desk top study. This look at data that is currently available on the site such as historical maps, geological data, records of pollution incidents to describe the site and any potential sources of pollution. This will allow the initial conceptual model to be constructed. This looks at pollution sources, receptors –such as site residents or groundwater, and any pathways linking the two. If these elements are present then there is a pollutant linkage. Only if a source, pathway and receptor are present can the site be said to be contaminated – if one of these are missing, it does not meet the legal definition of contaminated land. This then forms the preliminary risk assessment. As part of the desk study process, a site walkover survey is normally undertaken to make an inspection of the site to assess visual evidence for contamination, nearby receptors and so on.

Should the desk top study phase conclude that there is likely to be a pollutant linkage present, then an intrusive investigation will need to take place. This will enable samples of soil to be retrieved using drilling rigs or excavators for laboratory analysis. It will also allow a visual inspection and classification of the soils which is critical in determining how the contaminants may act and therefore the risk they may pose. At this stage, groundwater monitoring wells may be installed to allow water samples to be taken and groundwater depth to be measured. The information that is gathered enables a further stage of risk assessment to be undertaken and judging whether there is likely to be an actual risk to the receptors that are present.

So why bother with a desk top study – cant we just get somebody to get some samples?


Two reasons – the first is that the planners will not accept the intrusive investigation without the desk study having been carried out first. This will mean that it will have to be carried out retrospectively leading to delays and the possibility that the intrusive investigation may then have to be re-done which could be expensive! There is a good reason for this – the desk study can provide information on the likely type of contamination, sometimes the location, what techniques are best for sampling, whether monitoring wells are needed, whether there are underground storage tanks. This is all essential information when planning a site investigation and can potentially save substantial amount of money. Secondly, the desk top study may show that no intrusive investigation is required- saving an even greater sum of money. Furthermore it is critical that if any sampling is carried out in the appropriate manner for the site and the contaminant involved – without the desk top study being carried out it may be impossible to decide what is appropriate.

How much does remediation cost?


This is impossible to answer without looking at the site, the contamination that exists and the nature of the development. It used to be the case that you could just dig out the contaminated soil and transport it off site. This is now discouraged and is becoming more expensive with landfill tax increases. Fortunately there are a wide variety of techniques that can be used to tackle contaminated land. The actual technique used will depend very much on the contaminant and the physical/chemical characteristics of the soil. Consequently, there is no single technique that will work for all sites.

Dr. Richard Wesson
of
Wesson Environmental

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