Contaminated Land

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Any construction project built on greenfield land is not sustainable. No matter how laudable the rest of the project may be, the use of undeveloped land for construction is indefensible. As our cities grow ever outward, leaving derelict urban gap sites behind them and devouring more and more "green belt" land every day, there is no way that a project which aims to be sustainable can be built on anything other than re-used land.

The issues involved here are as complex as other aspects of Sustainable Construction. The destruction of agricultural land becomes ever more serious as we begin to realise that intensive farming methods have serious drawbacks: development of more environmentally responsible agricultural practices will almost certainly require a larger area of good quality farmland. Also, the development of dormitory towns and out-of-town shopping centres is rarely matched by appropriate sustainable development of communication links, causing knock-on effects such as pollution, congestion, traffic-related illnesses and deaths.

The terms "contaminated land" and "brownfield site" convey a perception of risk to developers that is no longer warranted. The assessment and remediation of these sites is now a major international business. Guarantees and indemnities are available on remediated sites and the economics of development of these sites is attractive. This is demonstrated by the fact that over half of all residential development nation-wide is on re-used sites. Residential development is the most sensitive end use to which these sites can be put, yet it is now more common than not to build houses on "contaminated" land.

Site Investigation

A contaminated land investigation typically consists of discrete stages. The first is a desk study, using historical information to establish past uses of the site and its surroundings to give a general feel for the likelihood of contaminative risks.

In addition, information from statutory bodies and local authorities about the site and surrounding areas is reviewed, including data regarding the location of landfill sites, water quality classifications and site investigation reports. A review of the geology and hydrology of the site is usually undertaken as part of a geotechnical investigation, and this information is used as a means of identifying the potential residence and migration of contamination to and from the site.

The potential is considered for contamination and risks to future users of the site and to areas outwith the site. Site conditions are assessed to determine:

present-day usage,
adjacent activities that could have potential environmental impacts on the site,
potential site hazards, site safety and access requirements for any plant and equipment required for future site works.

Many water authorities and companies now require that all new services must be laid in uncontaminated ground. Developers are required to demonstrate that service runs are uncontaminated by providing chemical data on ground conditions, as well as the presence of groundwater and soil gases. As of July 1999, local authorities are required to build up a database of contaminated land within their area. To assist them in this considerable task, many are asking that their planning departments require an environmental site investigation for any proposed change of use, regardless of site history.

The second stage is an investigation of the nature and extent of contamination actually found on the site. This will typically involve intrusive investigations using trial pits, boreholes and gas bar probes. Soil and groundwater samples are taken and analysed for a range of chemical parameters. The chemical parameters will depend to some extent on the past uses of the site, as certain uses imply certain types of contamination. Some examples are given below:

Former use of site Typical contaminants
Agriculture Pesticides, herbicides, fungicides etc., hazardous gases and putrescible wastes, pathogens (e.g. anthrax), oils, organophosphates, synthetic pyrethroids etc.
Asbestos Works Asbestos dust, sheets and sludge
Asphalt Works Bitumen, kerosene, solvents, hydrochloric acid, fuels and oils
Chemical Works Depends on specific chemicals used and manufactured
Petrochemicals VOCs
Chlor-alkali Works Mercury, chlorine
Acid Manufacturing Iron pyrites, spent oxides
Pesticides Manufacturing Aliphatic, aromatic and chlorinated hydrocarbons, solvents
Fertiliser Manufacturing Hazardous gas, sulphates, ammonia, anthrax (from bones), solvents and heavy metals, particularly copper, cadmium, manganese, molybdenum and zinc.
Pharmaceutical Solvents
Coal Mining Leachate containing iron, aluminium, chlorides and sulphates
Coke Works Coal tars, phenols, sulphates, cyanides, ammoniacal liquor
Food processing Alkaline solutions, putrescible wastes
Gas works Coal tars, phenols, sulphates, cyanides, ammoniacal liquor
Glass Manufacturing Lead, fluorides, oil, acids, arsenic, antimony and chromium
Iron and Steel Works Coal tars, phenols, sulphates, cyanides, ammoniacal liquor, sulphides, solvents, hydrochloric and sulphuric acids, chromium, zinc and cadmium
Landfill Sites Various residual contaminants, hazardous gas generation and leachate of variable composition
Lead Works Heavy metals, particularly lead, zinc, antimony and cadmium
Mechanical Engineering Metal dross and lubricants, acids, heavy metals and degreasing agents
Metal Finishing Solvents, hydrochloric and sulphuric acids, chromium, zinc and cadmium
Metal Mining and Smelting Pyrites, heavy metals, VOCs, fuel oils and lubricants, slags and other residues
Mineral Workings VOCs, fuel oils and lubricants
Paint and Ink Manufacturing Pigments containing heavy metals, oils, resins, mercury-based pesticides and solvents
Petrol Stations VOCs, petrol and diesel, engine oils, degreasing solvents and anti-freeze
Power stations Pulverised Fuel Ash (PFA), coal residues, oil, asbestos and PCBs
Printing Works Heavy metals, particularly chromium, magnesium, zinc, silver and inorganic acids, VOCs
Pulp and Paper Manufacturing Mercury, alkalis, solvents, pigments containing heavy metals, especially chromium, cadmium and zinc, hazardous gases, organics and solvents
Railway Land Hazardous gas, waste ash, clinker, wooden sleepers, metals, oils, asbestos (from brake linings), diesel, lubricants and preservatives
Residential etc. Metals, organics and hazardous gas generation, principally from making up levels using imported fill material
Scrap Yards Metals, VOCs, organics, PCBs, asbestos, oils and fuels
Sewage Works Coke, clinker, slag, sand and gravel, hazardous gas, organics, pathogens and heavy metals
Shipbreaking VOCs, metals, PCBs, radioactive materials, asbestos, oils and additives
Shipbuilding Metals, oils and paints, phenols in foundry sand
Tanneries Acids, solvents, chomium, pesticides, sulphuric acid, arsenic
Textiles Phenols, sulphide, solvents, oils and detergents, acids, chromium, cadmium and zinc
Timber Treatment Insecticides, fungicides, creosote, organic solvents, mercury, chromium and arsenic

The laboratory chemical test results are usually compared with the guidelines given by the Inter-departmental Committee on the Redevelopment of Contaminated Land ICRCL (Guidance Note 59/83).

Analysis of Chemical Data

The ICRCL publication introduced the concept of Trigger concentrations (Threshold and Action) to assist in determining the extent to which a site is contaminated. Assigned Trigger concentrations vary depending on the proposed end use of the land. For domestic developments where risks exist of direct ingestion of soil or consumption of contaminated food grown on the site, the acceptable levels are lower than for commercial or industrial development where these risks are less.

The significance of concentrations of contaminants in relation to the ICRCL Guidelines is discussed below.

Below the Threshold Trigger level, contamination can normally be regarded as presenting a low risk for a particular end use even though the level of contaminant may be higher than the background level typical of the area. No remedial action is therefore required.
Between the Threshold Trigger and Action Trigger levels the degree of contamination may not necessarily present a risk for a particular end use but evaluation of any potential risk is required in order to determine whether or not any remedial action should be undertaken.
Above the Action Level the degree of contamination is such that its presence is undesirable or even unacceptable and remedial action should be taken. The site should be regarded as contaminated.

If the remediation options for a particular end use are unacceptable then a re-assessment may be necessary in order to examine alternative use of the site.

ICRCL distinguish between Group A contaminants, which may pose hazards to human health, and Group B contaminants which are phytotoxic (poisonous to plants) but are not normally hazardous to human health.

It should be noted that not all potential contaminants are covered by the ICRCL Guidance Note 59/83. Where other contaminants are present reference must be made to other published criteria such as the Greater London Council (GLC) Guidelines and Dutch Guidelines.

New, updated guidance is expected to be enforced around the middle of 1999, as a result of legislation introduced in the Environment Act 1995.

Soil Gas

The site will usually also be investigated for soil gases. Gas can diffuse up to near-surface layers from underlying coal and shale seams. It can also be generated by micro-organisms in the soil through biodegradation of organic materials. In either event, harmful concentrations of gas can build up in the soil and particularly in voids beneath and within buildings.

In the majority of cases, the main gases produced are methane and carbon dioxide. These gases are produced in differing ratios depending on the amount of oxygen present within the ground.

When flammable gases are mixed with air at certain concentration known as the flammable or explosive range, the mixtures may ignite to produce fires and explosions. The investigation analysed gas from a number of trial pits and boreholes for these gases.

If present in sufficient concentrations, carbon dioxide can cause a risk of asphyxiation, especially when the oxygen levels are less than 18% by volume. Guidelines specified in the Health & Safety Guidance Note EH40, Occupational Exposure Limits, state a short-term carbon dioxide exposure limit of 1.5% by volume over 10 minutes, with an occupational exposure level standard of 0.5% by volume over 8 hours. Building Regulations Addendum C suggests specific design measures where carbon dioxide concentrations exceed 5% by volume.

Source-Pathway Receptor Analysis

The risk to a proposed development from contaminated land is usually assessed using Source-Pathway-Receptor analysis. This technique establishes the presence of a chain of events required to present a risk.

First, a source of risk is required. In this context, this means the discovery of one or more chemical parameters in excess of guidance limits or an excess of soil gas. Once a source is discovered on site, the investigation will analyse the presence of any Pathways by which this source can be transmitted to a sensitive receptor. Such pathways include direct ingestion, aerosol exposure, contact etc.

Once a Source and a Pathway have been established, the final link in the chain is a Receptor. A Receptor is essentially anything or anyone that can be adversely affected by the contamination. This includes a building’s occupants, the fabric of the building itself, landscaping plants, local watercourses etc. The Receptor (and indeed the Source) need not be within the boundaries of the site itself. Particularly in areas where the underlying drift geology is relatively porous, the potential exists for contamination to spread to the site from surrounding areas and to surrounding areas from the site.

This means, for example, that a clean site near a landfill site may be affected by soil gas migrating onto the site, even when the site itself has never been put to any potentially contaminative use in the past. Similarly, a contaminated site may adversely affect the quality of a nearby river by runoff or contamination of groundwater.

Remediation

All these considerations and more must be borne in mind when drawing up a remediation strategy. The nature of this strategy can vary enormously, depending on the size and location of the site, the extent and nature of contamination and the design and use of the proposed development, among other factors. One common theme, however is that it is possible and practical to remediate the vast majority of brownfield sites economically and effectively.

There is no need for brownfield development to carry any additional risk or liability. Brownfield sites often offer excellent locations at good prices and remediation of such land can be counted as a net benefit to the environment, which is rare indeed.

More detailed information is available from Alistair Jamieson.