One of our more unusual site investigations has recently been completed. We were called out to a site where a helicopter had crashed some days previously, in the middle of a field. The helicopter had caught fire and thankfully nobody was hurt. As a consequence, there had been spillage of aviation fuel and the fire brigade had attended to control the fire. In addition to petroleum hydrocarbon contamination in the soils, we suspected that Per and Polyfluoroalkyl Substances (PFAS) may be present originating from the fire fighting foam. We carried out window sampling to recover samples and determine the contaminant distribution, screening each sample using a photo-ionisation detector (PID) and submitting samples for laboratory analysis.

Risk assessment was a little different to most sites as the concern was over potential impacts on crops as opposed to human health due to the location being fairly remote, and people being unlikely to come into contact with soils. By working out the contaminant distribution, we were able to come up with a remedial strategy that will be implemented in due course.

Many people, especially those who do not have experience with the specific issues surrounding these sites often assume that contamination will not be a problem when applying for planning permission or developing these sites. Consequently, they may involve us quite late in the process stating ‘there are no contamination issues, there has only been orchard/sheep/vehicle storage here’. This may not be the case and there may be multiple issues related to contaminated soils present on the site.

So, if the site in question has not been used for industrial purposes, where do issues with contaminated land arise from? Well, in common with many kind of human activity, there is the potential to have an impact on the environment. Let us have a look at the main soil contamination issues that we have encountered.

Pesticides

This is what everybody associates with farms and environmental impacts. However, these may not necessarily impact the site soils. There seems to be a perception that contamination involves drums of ‘chemicals’ lying around and leaking their contents into the ground and rivers. This makes great pictorial copy for campaigning organisations, but consider this – farmers are running a business. Why would they allow drums of expensive materials to disgorge their contents everywhere when they are frequently struggling financially? Makes no business sense does it?   Likewise, they do not chase livestock around fields trying to apply pesticides as this would waste substantial amounts of these materials.

This does not rule out the presence of pesticides in soils however. If they have been incorrectly stored for whatever reason, they may be present in site soils. Poor controls on their use may also responsible, especially if casual labour has been employed. Where sheep dips are present, contamination of soils in and around these features may be present with the predominant compounds used being organophosphorus compounds and synthetic pyrethroids. ‘But’, I hear you say, ‘there was only organic farming here’. This does not preclude the use of pesticides with copper compounds, sulphur, rotenone and pyrethrums.

Asbestos

This is often used on agricultural buildings for roofing and for cladding in the form of cement bonded asbestos normally containing chrysotile (white) asbestos. However, other forms of asbestos may have been used. When sites are being redeveloped, they may be in a derelict condition with the asbestos being broken either through wear on the building or through vandalism. This can lead to asbestos fibres being present in site soils and this is where the risk comes from – inhalation of asbestos fibres both during development and during subsequent site use.

Heavy metals

On farms? Well yes. As discussed in the pesticides section copper compounds may be used as pesticides and have been for years. There are other sources that may surprise people who are not used to dealing with rural sites however. Clients will sometimes state ‘there wont be any problems here it has always been orchard’. That may be precisely where the problem lies. In the good old days before these nasty synthetic pesticides came about that seem to cause so much concern to the public, more traditional solutions were used. Unfortunately these included lead arsenate (a compound containing lead and arsenic) to combat codling moth, and the charmingly named Paris green – (copper(II) acetate triarsenite or copper(II) acetoarsenite. Needless to say, when these were sprayed on the orchards, some directly impacted soils whilst much of it was present on leaves and fruit. The leaves and fruit would fall -and rot – whilst of course the lead and arsenic being elements, did not rot. Consequently, lead and arsenic can become very concentrated in these areas. Surprisingly, arsenic was also used as a growth promoter in poultry feed and we understand still is in some countries, including the US. This is ingested and excreted in their faeces. The faeces naturally rots away, but of course the arsenic remains behind – again causing elevated concentrations in site soils.

Petroleum hydrocarbon compounds

These can result as a consequence of poorly managed fuel oil storage including both heating oil and red diesel. We frequently see older, metal, single skinned above ground storage tanks with no bunding present. These and the associated pipework can leak and where refilling of the tanks has been poorly managed or that of vehicles soils may be impacted.

Polycyclic aromatic hydrocarbons (PAH)

These are very common contaminants that result from the burning or organic (i.e. carbon containing) materials such as paper, wood and other vegetative materials. In the past waste may have been burned and ashes may have been used as a soil improver. These can all lead to the presence of PAH compounds in soils. Other burning activities such as stubble burning can also lead to the aerial deposition of these compounds in soils.

Depending on the site features, geology etc these contaminants may pose a risk to future site users and to controlled waters. In the case of the latter this will include groundwater (underlying aquifers) and also surface water such as rivers. Whilst a river may be distant from the site, there may be drainage ditches on or adjacent to the site that may allow migration of contaminants from the site. Other issues may include generation of ground gas. This will occur where putrescible materials have been buried – i.e. those that will readily rot away such as vegetative matter. This may be present on the site where land has been infilled or offsite where landfilling operations have taken place.

What is essential is that the site is investigated in the appropriate manner. Please feel to contact us to discuss in more detail the specific site you may be dealing with.

Firstly, whoever is doing the site investigation must be independent of the client. If not, there are all sorts of conflict of interest possible. If somebody has a vested interest in showing that the site is not contaminated (or in some cases is contaminated), then there is the potential that they could substitute soils for those from elsewhere that are more likely to provide the desired outcome.

Secondly, when we are on site we do not simply put soil into a bag and hope for the best. Samples must be placed into appropriate containers for the contaminant being analysed for. Normally we will put samples into a number of containers. Plastic tubs are used where inorganic contaminants such as metals or asbestos are being analysed for. However, in the case of organic contaminants such as petroleum hydrocarbons, volatile organic carbons etc, these may be absorbed into the plastic and lead to the analysis showing lower concentrations in the soil than are actually present. Furthermore, where volatile compounds are present, it is important to eliminate head space in the container to prevent volatilisation of the compounds which again leads to lower concentrations being shown.

Thirdly, when we are are site, we are also recording other data. In many cases this is visual. Correctly logging the borehole or trial pit so that the soil type or rock type is properly described is critical and is important to the overall site investigation and conceptual site model. However, we may also record other visual information such as visual evidence of contamination in the trial pit or on the site surface, water running on or off the site, smells that indicate contamination etc. This in turn enables us to target our sampling to different depths or it may mean we we sample from a different part of the site. If a layman was to take a soil sample – how will they choose the appropriate depth or location without a background in this area? Being on site may also give us the opportunity to carry out on site test such as using a photo-ionisation detector to determine whether volatile compounds are in soils. This may greatly reduce the cost of laboratory analysis hilst allowing a more thorough investigation

Fourthly, is the sampling pattern appropriate? Is it targeted or is random stratified sampling to be used? This will normally be decided prior to going on site so you may think that we could give you a plan of sample locations and let you get on with it. However, how do we know that the samples are from where you say they are? Again, independence is critical. Another point is that when we get on site, there are occasions when a location that we wish to target is inaccessible. Therefore we may have to rethink locations. Conversely, observations on site (e.g. breather pipes unearthed, oil water separators discovered, unexpected tanks or drainage features observed) may lead us to carrying out sampling in locations that we were not aware of previously. If somebody experienced is not and a subsequent problem is discovered, this may lead to further cost and delay.

Finally, we are not a laboratory – we send sample to a 3rd party for analysis due to the very expensive, specialised equipment involved. If a sample is sent to us and we just send it on, we don’t make any money! I am sure my readers will agree, as a business, this would be very bad practice!

There are other related things which I am sure will occur to me at a later date. The above I think, details the primary reasons however.

Contaminated land site investigation is very much a process. We have produced the below flow chart to explain where various parts of the site investigation fit including the desktop study, intrusive investigation with soil sampling through to remediation. We hope this helps to clarify how various parts of contaminated land risk assessment and management interact.

If you need more information on the site investigation process or contaminated land in general, please contact us.

What does a site investigation involve?

A site investigation is a way of determining whether the soils in a certain location might pose a risk to future site users or to the wider environment. The wider environment can include nearby sites, surface water such as rivers, groundwater (i.e. sub-surface aquifers), or ecological receptors such living organisms or protected sites. All of these elements that may be harmed are known as receptors.

In simple terms, it involves looking at all of the factors that may lead to harm to any of the above receptors. This includes looking at a very wide range of documentary data as well as sampling soils and observing site conditions.

Site investigations must be carried out in the correct and follow UK Guidelines such as CLR 11.

Reports that do not follow the current guidelines will not be accepted by the regulators and consequently will not allow a planning condition to be discharged.

The site investigation process

There are 3 main processes when dealing with contaminated land as outlined below. These must be carried out in sequence with each stage building on the previous stage. These stages are as follows:

1. Phase 1 Investigation – also known as a desktop study.

This involves a review of documentary data including site history, geology, hydrogeology, landfill records, industrial activity records etc. A site walkover is normally carried out to allow a visual inspection of the study area and surroundings. This is then used to produce a ‘conceptual site model’ that describes how contaminants, if present in soils, may interact with receptors via pathways such as ingestion of soils, vapour intrusion into buildings, inhalation of dust, leaching into an aquifer, migrating laterally to a river etc. This forms the preliminary risk assessment or PRO. Where a contaminant source, a pathway and a receptor are present, this is described as a pollution linkage.

It should be noted that a simple Homecheck/Sitecheck report that just lists data will not be accepted by the regulator.

If no pollution linkage is identified, then there is no requirement to carry out further stages of investigation.

2. Phase 2 Investigation – also known as an intrusive investigation

This must be based on the scope identified in the phase 1 investigation. This stage involves physically taking soil samples for laboratory analysis. It also will involve the soils/rock encountered being logged in the correct manner and possibly monitoring wells being installed. Samples must be collected in the correct manner, in the correct containers and stored in a way that degradation does not take place. This must all be recorded by the site engineer along with details of sample location. The data is used to produce a report which will include   a risk assessment comparing soil concentrations to national guidelines and possibly to custom generated guideline values where necessary. Modelling of contaminant transport may be necessary. The data and the risk assessment will be used to refine the conceptual model. The intrusive investigation may sometimes involve several stages depending on the site.

If the phase 2 investigation indicates that there is a significant risk arising from contamination of the site, then remediation will be necessary.

3. Remediation

This involves what people think of as cleaning up the site. Many people think it is a case of simply digging soil out and replacing it with clean soil. However, this option may be very expensive and may be an unnecessary option. There are a wide range of techniques available, but the key is to break the link between the contaminant source and the receptor. On some occasions changes in site layout may achieve this. However, what is critical is tackling this as early as possible so the best and most cost effective method can be selected.

If you require advice on any of these stages, please do not hesitate to contact us for free initial advice.