The Environment agency estimates that there are some 300,000 hectares of land in the UK affected to by contamination left by industrial activity alone. Contaminated land is a general term used to describe land containing substances that, when present in sufficient concentrations, are likely to cause harm to man, the environment, or materials used in construction. This contamination can manifest in soil, in air, as a waterborne hazard or as a combination of these.
Contaminated land is a fact of life for the developer or builder, but whether it has become contaminated by a naturally occurring means, or is a man made problem, the resulting needs are the same. With contaminated land there will be a need for assessment of the situation, and this is going to include discovering the source or sources of that contamination and identifying the extent and combination of the hazards involved. Thereafter will follow a need to clean and recheck the site before change of use or building commences, firstly for the protection of site workers, and eventually for the longer term safety of those destined to inhabit premises built on such land.
Where has contamination come from?
There are numerous industrial and man made sources of contamination, and these are not always visible. No area is immune as while cities suffer from contamination caused by development and former production centres, rural sites may suffer as a result of waste disposal, or uncontrolled use of pesticides and fertilizers.
Examples of sources of contamination from man’s activities are:
- Waste disposal sites, such as landfill and scrapyards
Possible contamination by organic gases, potentially flammable, explosive and toxic gases, biological matter and bioaerosols such as mould growth and spores.
Landfill gases, although often smelly, can pose a threat even under the odour threshold, highlighting the fact that contamination may be present even when invisible to inspection by eye alone. This highlights the need to take a more scientific approach to monitoring hazards at proposed development sites.
|Common Landfill Gas Components with Odour Thresholds|
|Component||Odour Description||Odour Threshold (parts per billion)|
|Hydrogen Sulfide||Strong rotten egg smell||0.5 to 1|
|Ammonia||Pungent acidic or suffocating odour||1,000 to 5,000|
|Benzene||Paint thinner-like odour||840|
|Dichloroethylene||Sweet, ether-like, slightly acrid odour||85|
|Ethylbenzene||Aromatic odour like benzene||90 to 600|
|Toluene||Aromatic odour like benzene||10,000 to 15,000|
|Trichloroethylene||Sweet, chloroform-like odour||21,400|
|Tetrachloroethylene||Sweet, ether-or chloroform-like odour||50,000|
|Vinyl Chloride||Faintly sweet odour||10,000 to 20,000|
From waste collected in scrapyards, a variety of metals may be present. Cadmium, lead, arsenic and mercury are all hazardous to health. It is interesting to note that at ‘hazardous’ waste sites much of this material is logged, yet at a municipal or household dump it seems that ‘anything goes’.
Householders may use rubbish collections to dispose of any material – often without thought to the contents and the risk it could pose. This means landfills will be contaminated by left over paints, solvents, chemicals from heavy duty domestic cleaning products (often highly acidic or alkali) and batteries (containing nickel cadmium).
- Power industries – from gasworks to oil refineries, and mining
Possible contamination by left over combustibles, sulphur which presents a fire risk, gases such as phenols or solvents which are toxic, heavy metals, dioxins and PCBs.
- Manufacturing industries, pharmaceuticals, printing, foundries
Possible contamination from left over raw materials, inks and solvents in printing, chemical hazards and metals from foundries, dyes and solvents from manufacturing.
So how did this contamination happen?
The contamination on land has resulted either from accidental leakage or spillage, disposal of raw materials or from uncontrolled demolition of industrial plants. Asbestos might also have been present in any older demolished premises, and form part of the contaminated rubble. Some areas suffer with toxic gas build up due simply to natural conditions. These might include hazards such as methane and radon.
However it happened, it is not always the case that these sources of contamination will be obvious. The unsuspecting new landowner must make it their priority to research and assess what contamination could be present.
Why does contamination become a hazard?
The ill health of the users or occupiers of land is clearly undesirable, and can occur in different forms from contamination, through inhalation of hazardous gases or by direct physical harm such as explosion from landfill gas build up. Explosions and fires have occurred under houses built close by former landfills at Loscoe, in Derbyshire in 1986, and in Kenilworth, Warwickshire in 1898.
All of these routes will expose humans to the dangers arising from contamination in its’ various forms
- Vapour or gas path to the surface directly, or via adjoining land
- Direct ingestion, by inhalation
- Travel to water supplies – harm to the environment and water quality
- Direct uptake into the regular food chain – via animals or crops
- Direct ingestion – via soil attached to home grown vegetables
- By other contact e.g. with building materials
- Harm to structures such as chemical attack on building materials could also mean costly repairs or – if left undetected – ultimately danger to the inhabitants from unsafe structures
- Direct dermal contact and uptake from skin contaminated by unknowingly touching affected materials
Assessing the risks – what equipment and techniques are available?
An assessment of the level of contamination can be performed using a range of monitoring tools. The tool used will depend on the hazards likely or assumed to be present, and the format in which they are present.
Consideration should be given to soil, air and water. In addition, thought needs to be given to the level and nature of the hazards, and whether they might be specifically categorised as a higher risk. This might affect the monitoring technique used or the way in which people are protected while carrying out monitoring and reclamation. Higher risk might mean contaminants which are:-
- Potentially explosive
- Acutely toxic – immediately & potentially fatal
- Long term toxic – effects over time
Monitoring generally means the use of fixed equipment with either datalogging capabilities or modem links to send data back to the surveyor. Sampling requires the presence of personnel and is obviously time dependant. Sampling tends to be the cheaper option. This section covers soil, water, and air but concentrates in depth on airborne contamination.
Contamination in soil and rubble
In the 1980s, the UK was one of the first countries to propose ‘trigger’ concentrations of certain contaminants in soil, which if exceeded, would prompt further investigation. In 1992 in response to a House of Commons Select Committee on the Environment report the then Department of the Environment initiated more research. This was to develop a scientific framework, for assessing the risks to human health from land contamination.
The first outputs of this research programme were launched on the 14th March 2002 at the Barbican Centre, London. The package consists of four main reports (CLR 7, 8, 9 and 10) and supporting toxicology reviews and Soil Guideline Values (SGVs) for individual substances.
- CLR7: Assessment of risks to human health from land contamination. An overview of the development of guideline values and related research
- CLR8: Potential contaminants for the assessment of land
- CLR9: Contaminants in soil. Collation of toxicological data and intake values for humans
- TOX: Toxicological reports
- CLR10: The Contaminated Land Exposure Assessment (CLEA) model. Technical basis and algorithms (includes software)
- SGV: Soil Guideline Values
Information on these, and the documents referred to, is available to download in Adobe PDF format on the environment agency website at www.defra.gov.uk
Soil samples can be collected in a suitable receptacle and analysed in a laboratory.
For heavy metals this would mean using extraction and analytical techniques such as atomic absorption (AA). This can be a lengthy process on a large site. Contamination in soil is potentially layered within rubble to some depth, and the full picture is not evident from the examination of surface material alone.
Portable X-Ray fluorescence (XRF) analysers are increasingly used and will identify a wide range of metallic elements in soil, solid and liquid samples. In contaminated land remediation, the XRF analyser can be used to assess the in-situ soil contamination – ideal for brownfield sites prior to redevelopment. Contamination such as chromium, nickel, copper and zinc from an electroplating works would be easily identified, and as the surface is stripped, the depth to which metals have leached into the soil could be assessed. As material is removed, the XRF analyser is used in-situ, either on the ground surface or directly onto removed material.
Surface wipes may also be used to test for the presence of heavy metals. In the case of demolished premises, paint on woodwork could be checked for lead.
Contamination in water
Water samples collected in a suitable receptacle will be returned to a laboratory for analysis. Water sampling cassettes are also available. For heavy metals, the XRF analyser described under soils will provide quick on site results in liquids also.
However, contamination in soil and water is not the only problem. A variety of undesirable gases will be given off from former landfill and industrial processes – and not all of these emit a tell-tale smell at the levels in which they could be present.
Contamination in air – typical air sampling applications
Gas sampling via collection in bags
These are widely used for taking both short-term ‘grab samples’ for insidious, or noxious gases, or for longer term over 24-48 hours for spasmodic occurrences.
For a grab sample a small vacuum tube enclosing a bag allows a sample to be taken without the need for a pump. For longer term, a bag would be filled with a pump. The pump is set to a low flow over a period of time, which is calculated so as not to overfill and burst the bag. Bags are available in many sizes, but for practical purposes bags from a half litre to 20 litres are typically used.
The ‘whole air sample’ that a bag collects is then analysed to establish the contents.
Bag samples cannot be kept long term so quick transport to the laboratory for analysis is recommended, and commonly gas chromatography is used. Increasingly a portable photoionisation detector (P.I.D.) may be utilised onsite from the contents of a bag. A single P.I.D. instrument will typically be able to identify 250+ gases rapidly and down to parts per billions (ppb) level. On most P.I.D. units, gases are quickly selected from an in-built menu, listed alphabetically. Once the gas is selected, the P.I.D. does not need a long warm up time. It is ready to take measurements and responds quickly to the presence of the gas.
Gas sampling via tube collection
Air is pulled through a tube containing sorbent material. A variety of sorbents are available, most being specific to a chemical group, so the correct tube needs to be pre-selected. Single tubes are available for a wide range of gases, and appropriate methods of sampling and analysing are well established.
However, if the wrong hazard has been indicated or assumed from an initial survey or site history data, the incorrect tube could be used and may present low or no results when analysed. Mixed bed tubes can help by giving more than one chance as they will collect a range of chemical groups.
All sorbent tubes require laboratory analysis, typically by a gas chromatography method. Phenols, solvents, and amines would be among the gases appropriate to collect via tube sampling. Tubes usually have good storage properties and will keep if refrigerated for reasonable periods of time, being an advantage over a bag sample.
Gas sampling via passive badge collection
Badges can be used for intrusive situations, and require little action, training or maintenance. They have a low initial cost, and are analysed in a laboratory in the same way as a sorbent tube.
Newer badges coming onto the market for analysis following thermal desorption (where the badge is heated to release the gas during analysis) give lower levels of detection than previously offered with passive samplers.
Direct reading for gas detection
1) Gas sampling via colour detector tube
For a quick result and for ease of use, colour tubes are a simple choice for a survey. Used with a grab sample pump, or passively, depending on the tube type, colour tubes give an indication against a scale which is pre-printed on the tube. Like sorbent tubes these tend to be specific to a chemical group so assumptions need to be made about what gas is likely to be present in order to select a tube. A wide range of gases including hydrocarbons, ammonia, carbon dioxide and aldehydes may be detected.
2) Instruments such as P.I.D. , Gas Chromatograms and detectors with electro-chemical sensors
These can be useful for a more accurate result, and in the case of many direct reading instruments, to detect a variety of gases with the same equipment. With a P.I.D. you could expect to search for 250+ gases. With a gas detector methane or hydrogen sulphide would be possibilities.
Particle collection on filters from air
These samples rely on a pumped sample through a sampling head containing a suitable filter paper. If land has or is being disturbed, dust with any present materials will become airborne. Filters can be analysed gravimetrically to assess the airborne levels, however it is likely to be more important to know what the particulate comprises. This is possible if the laboratory is made aware of what to look for when analysing, as they will choose the relevant technique.
Asbestos would be sampled for in a similar way using filters, but the analysis technique will differ. Fibre counting is performed for analysis, and a specific type of gridded filter needs to be used to ensure this is possible. As with tubes, many validated methods exist so there are references and guidance available from the Environmental Protection Agency (EPA), Health & Safety Executive (HSE) and others, allowing the correct filter or tube to be chosen. If there is any doubt about the method or technique to use, laboratory or supplier advice should be sought prior to purchasing sampling media or devices.
Other types of contamination
From landfill, waste sites, sewerage works or tanneries, biological material could be present. When looking for spores or bacteria, filter methods exist. These types of contamination may be swabbed if visible, or if airborne will need to impacted or filtered onto a specific media. This could be media such as gelatine or agar capable of sustaining the material viable (alive). This is due to the analysis technique. Biological material may need to be allowed to grow on under laboratory conditions before it is possible to analyse and detect the species of bacteria or fungi present.
These are closely controlled under the radioactive substances act of 1960, and should not be encountered. However on an older site, these could be present from industrial processes involving processing of metals containing radioactive materials. These can be sampled by direct reading or with specialist static samplers. Further advice should be sought on this issue before taking any action.
The topic of contaminated land is somewhat vast. This article has sought to create awareness of risk by highlighting the potential dangers which must be considered and by reviewing a selection of techniques applicable to identifying and quantifying these hazards.
Many information sources are available, and some suggested sources have been given below, which were considered useful in the research for this article.
References & Further Information
‘Contaminated land: risks to Health & Building Integrity’, Ian F Viney and John F Rees
From ‘Buildings and Health’ ISBN 0 947877 78 9
Contaminated Land Assessment Model fact sheet for the Contaminated Land Exposure Assessment (CLEA) 2002 model
Rachel’s Environment and Health Weekly [email protected]
Environmental Protection Agency (EPA) resources online at
Published: 10th Mar 2005 in AWE International