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Contaminated land for construction

Revision as of 09:11, 23 April 2013

Contaminated land is land that presents a hazard in the form of material that has the potential for harm. A landfill site might be an example of contaminated land.

Assessment of the risk of harm is based on the likelihood, frequency and seriousness of specified adverse consequences.

Problems associated with contaminated land:

Threats to human health.
Damage to flora and fauna.
Contamination of ground water.
Damage to foundations and structures.
Settlement
Subsidence.
Migration of contaminants to adjacent land.

Clean up strategies include:

Source removal by transferring the contamination to a registered alternative site.
Bioremediation using bacteria to destroy organic contaminants.
Soil vapour extraction using a technique of vacuum extraction which is particularly effective with volatile chemical such as petrol and chlorinated solvents.
In-situ Soil washing injecting clean water adjacent to contamination and extracting the contaminated water. There are concerns that the effectiveness of this technique has not lived up to expectations.
Pathway interdiction using high density polythene as a membrane both horizontally and vertically as a capping thus encapsulating the contaminants and separating them from new construction. A gas proof membrane was installed below the foundations of the 02 / Millennium Dome at Greenwich built on a disused gasworks site.

The introduction of the Environmental Protection Act has been the driving force behind the treatment of contaminated land. The main types of contaminant identified are:

Toxic or carcinogenic chemicals such as cyanide, arsenic, mercury and benzene.
Toxic or phytotoxic metals such as lead, chromium, nickel, copper, cadmium and zinc.
Organic contaminants such as oils, solvents and phenols.
Corrosive substances such as acids and sulphates.
Flammable, toxic or asphyxiating gases such as methane, hydrogen sulphide and carbon dioxide.
Combustible material.
Asbestos.
Radioactive substances.

Some likely sources of contamination are:

Mining and extraction industries.
Iron and steelworks.
Gasworks.
Power stations.
Metal treatment and finishing.
Chemical industries.
Scrap yards.
Petrol stations and refineries.
Fragmentation plants.
Paint and dyestuff industries.
Railway land, especially large sidings and depots.
Sewage farms and works.
Waste disposal sites and fly tips.
Cable burning and bonfire sites.
Dockyards and dock basins.
Ordinance and munition factories.

Desktop studies of site history should establish whether there is a need for further investigation. Sources for a desktop study might include:

Maps: Ordinance Survey (current and historical), geological survey maps and town plans.
Statutory authority and utilities data, such as; local authorities, river purification boards, the Health and Safety Executive and the National River Agency.
Trade information from directories and trade associations.
Photographic records, particularly aerial shots.
Technical data from public literature.
Knowledge gained from adjacent development.
Anecdotal information from libraries, local residents and local newspapers.
Meteorological, mining and hydro-geological records.

If the desk study raises concerns then trial pits and borehole investigations should be undertaken, concentrating on the areas of greatest suspicion incorporating a flexible strategy that provides a framework to cover the whole site.

The legal framework for contaminated land is incorporated in The Environmental Protection Act – contaminated land registers, under Section 143. Section 61 obligates a landowner to bring pollution to an end. Prosecutions can be brought about by state regulatory authorities for instance through Section 85 of the Water Resources Act.