A used and/or abandoned site, following censure of activities often contain several contaminants that pose immediate hazards or are capable of posing future hazards to human and ecological health. The contaminants (e.g. chemical substances) pose hazards because they exist at levels above the background levels or they exceed certain levels, pre-determined to be protective of human and ecological health.

Background level of a substance at a given location is the natural level that the substance exists at that location, without any foreign contribution of the substance to that location. You will never be able to remediate a substances below the background level it exists at a particular location. The background lconcentration of location A could be different from the background level at location B.

The pre-determined levels or "thresholds" or "cut-offs" or "clean-up criteria" are set by authorities having jurisdiction over a given community.Where a subtance exists at concentrations higher than the background levels, threshold concentrations above which the substance become dangerous to human, animal or plant's health needs to be set. Locations where the substance's concentration exceeds the threshold are considered contaminated and should be cleaned up to below the threshol value.

Contaminated (or Environmental) Site Assessment or investigation studies are required to establish the extent and magnitude of contamination on a site. The established magnitudes are compared to the pre-determined safe levels (clean-up) criteria to decide on whether or not a site is contaminated and delineate (or mark out) areas of contamination on a site. In cases of these exceedances of the background concentrations or the pre-determined levels, site clean up is required to reduce the contaminants to levels considered safe for human health and the ecology. This is particularly so where the used land will be reused for future projects or where there will be continuous access to the site by humans and animals.

Contaminants of Concerns

The contaminants of concerns on used sites depend on the previous activities (industrial, commercial or domestic) that took place at the site. The contaminants released to a site that was used as a gas station will be different from those released into a site where mining activities or ore processing took place. The broad category of contaminants that could be found on most contaminated sites include:

• Dilapidating Infrastructure - buildings, equipments, and other structures
• Hazardous chemicals/wastes
• Surface Debris / non-hazardous wastes
• Contaminated Soils - metals impacted soils; petroleum hydrocarbon (PHC) impacted soils or polychlorinated biphenyl (PCB) impacted soils
• Tailings and waste rocks
• Mine openings - adits, vent raises, shafts, exploration ditches/trenches

Dilapidating Infrastructure - buildings, equipments, and other structures:

Abandoned buildings and other infrastructures in states of disrepair, pose danger to human and animals. The buildings sometimes contain Hazardous chemicals/wastes that are either toxic, radioactive and dangerous (e.g. explosive or with the high potential of causing fire), injurious to human and animal health (e.g. cancerous etc).

Old structures, mostly pre-1970 built buildings and infrastructures contain asbestos, lead amended paints and/or polychlorinated biphenyl (PCB) amended paints. Asbestos, lead and PCB components of the paint pose continuous hazard to human and the ecology.

Abandoned dilapidating buildings are sources of non-hazardous wastes and debris posing physical hazards on old sites.

Contaminated Soils:

Used and abandoned sites contain soils contaminated by petroleum hydrocarbons. These would have resulted from spills and leaks of gasoline, kerosene, fuels, diesels, lubricating oils and similar products during the years of industrial activities at the site. Some soils at old sites also get contaminated by PCB, and metals such as Zinc, lead, cadmium.

Other features of used sites:

Other features of used sites requiring site clean up relates to specific sites such as mining and exploration sites. Such sites contain mine openings (adits, vent raises and exploration trenches), Tailings/tailings pond, waste rocks that may or may not be acid generating. These features pose physical hazards and chemical hazards to humans and ecology.

Site cleanup technologies reduce the contaminant levels or the levels of risks on used sites to levels pre-specified, by regional standards or site specific studies, as protective of humans and ecology.

Follow the links to the left for introductory information on Environmental Site Clean up including sections features on contaminated sites, common chemical contaminants, and the remediation technologies for reducing the common contaminants.