Contaminated land basics

There are a variety of mechanisms by which contamination may occur:

• leaks and spillages from tanks and pipes;
• contaminated surface runoff and flooding;
• accidents or spillages during storage and transport of raw materials, intermediate products and waste materials;
• disposal of waste materials on or adjacent to the site;
• stack omissions resulting in contamination of the surrounding environment;
• demolition of buildings which have contained contaminating material (e.g. asbestos lagging, impregnated brickwork);
• movement of contaminated surface or groundwater onto the site;
• migration of toxic or explosive gases from adjacent land or underlying strata;
• leaks from drains from process areas.

Further exposure or dispersal of contaminants may occur as a result of soil disturbance and movement, wind dispersal, or leaching through soils and drainage into surface drains and watercourses and groundwater.
Numerous historic, recent past and current land uses have the potential to contaminate sites. Some of the more significant uses are:

• fuel storage and filling stations;
• vehicle maintenance garages and depots;
• mining and extraction industries;
• iron and steelworks;
• metal treatment and finishing;
• chemical and pharmaceutical industries;
• oil refining and storage;
• timber treatment;
• railway land, especially large sidings and depots;
• scrapyards;
• cleaning, paint and dye stuff industries;
• sewage works and farms;
• fly tipping, cable burning and bonfires;
• landfill and waste disposal (hazardous and non-hazardous household wastes);
• dockyards and filled dock basins;
• electrical substations and goods manufacturing, e.g. use of chlorinated hydrocarbons, solvents and metals;
• industrial process emissions to air, soil and water.

Note: historical land uses were far less regulated and controlled than their modern counterparts.