Many industrial sites can be potential contaminated sites as a result of industrial development. Contaminated land can be found at many places such as motor workshops, petrol stations, fuel depots, railway yards, landfills, industrial sites and ex-mining land. Contaminated Land means a site at which a substance occur in, on or under the land at concentration. Above the concentration at which the substance is normally present in or on the land in the same locality and pose or are likely to pose an immediate or long term hazard to human health or the environment

The investigation, assessment and remediation of contaminated land should follow current best practice and should be carried out by a competent person with a recognized relevant qualification and sufficient experience in contaminated land i.e. an environmental consultant.

Preliminary risk assessment

Preliminary risk assessment is required to obtain a good understanding of a site's history, its setting and its potential to be affected by contamination. A Preliminary risk assessment comprises
1 a desk study,
2 a site walkover survey
3 a conceptual site model

Site investigation and risk assessment

For land properties which are not identified with any potential subsurface contamination during the initial assessment, it is recommended to conduct minimum baseline environmental site assessment to establish the background level of subsurface soil and groundwater quality for future reference, this is especially applicable for land properties that will be used for activities of polluting industries
If Preliminary risk assessment indicates that there is a potential for contamination, a Site investigation and risk assessment will be required. This step comprises site investigation and risk assessment, to determine whether there are any unacceptable risks to people, property or the environment.
In order to determine the vertical spread of contamination, soil and water samples shall be taken at various vertical depths at different locations on the site.

Boreholes

Boreholes to be used for groundwater monitoring should generally be drilled to a minimum depth of two metres below the water table and/or to suspected contamination depth and installed with well materials to allow for groundwater sampling.

Trial pits

Trail Pits or trenches can be used in conjunction with boreholes or on their own. The use of trial pits offers a quick method of investigating and inspecting a site. Trial pits can be excavated, by hand or mechanical excavator; however, trial pits should not be entered by anyone once the depth has equaled or exceeded 1.2 m unless appropriate safety precautions (i.e. shoring, stepping and/or sloping of sides) are taken.

Window sampling

Window sampling is carried out by drilling small diameter boreholes into the ground. The window sampler tubes are driven into the ground by hand held equipment or small rig. The maximum depth is usually around 5 metres.

Hand Augering

This method can be used to take soil samples from shallow depths. There are a number of types of auger, but it is typically a corkscrew spiral that is screwed into the ground. Samples can be taken at targeted soil depths and conveyed to the surface.

Field Test and Laboratory Test:

A variety of field or Lab tests/measurements may be used as a contribution to the screening of samples on contaminated sites to provide real-time data. The field results need to be augmented by chemical analysis and their use as the sole source of analytical data in the assessment of potentially contaminated sites is inappropriate as they may give falsely high or low results.

Selection of Remediation Method

Based on the findings of the site investigation, the need to remediate the site will be determined. The following factors should be considered when evaluating different remediation methods:

1 nature and level of contamination;
2 extent of contamination;
3 site characteristics (such as site hydrogeology, soil and groundwater chemical characteristics);
4 site constraints (such as available space, surrounding areas); and
5 time available for remediation.

Thermal desorption

Thermal desorption is a technology for soil remediation. During the process a desorber volatilizes the contaminants (e.g. oil, mercury or hydrocarbon) to separate them from especially soil or sludge. After that the contaminants can either be collected or destroyed in an offgas treatment system.

Excavation or dredging

Excavation processes can be as simple as hauling the contaminated soil to a regulated landfill, but can also involve aerating the excavated material in the case of volatile organic compounds (VOCs). Recently, ExSitu Chemical oxidation has also been utilized in the remediation of contaminated soil. This process involves the excavation of the contaminated area into large bermed areas where they are treated using chemical oxidation methods.

SEAR - surfactant enhanced aquifer remediation

Also known as Solubilization and recovery, the Surfactant Enhanced Aquifer Remediation process involves the injection of hydrocarbon mitigation agents or specialty surfactants into the subsurface to enhance desorption and recovery of bound up otherwise recalcitrant non aqueous phase liquid.

 Pump and treat

Pump and treat involves pumping out contaminated groundwater with the use of a submersible or vacuum pump, and allowing the extracted groundwater to be purified by slowly proceeding through a series of vessels that contain materials designed to adsorb the contaminants from the groundwater. For petroleum-contaminated sites this material is usually activated carbon in granular form. Chemical reagents such as flocculants followed by sand filters may also be used to decrease the contamination of groundwater. Air stripping is a method that can be effective for volatile pollutants such as BTEX compounds found in gasoline.

Depending on geology and soil type, pump and treat may be a good method to quickly reduce high concentrations of pollutants. It is more difficult to reach sufficiently low concentrations to satisfy remediation standards, due to the equilibrium of absorption (chemistry)/desorption processes in the soil. However, pump and treat is typically not the best form of remediation. It is expensive to treat the groundwater, and typically is a very slow process to cleanup a release with pump and treat.

Solidification and stabilization

Stabilization/solidification (S/S) is a remediation/treatment technology that relies on the reaction between a binder and soil to stop/prevent or reduce the mobility of contaminants. Conventional S/S is an established remediation technology for contaminated soils and treatment technology for hazardous wastes in many countries in the world.

Stabilization - involves the addition of reagents to a contaminated material (e.g. soil or sludge) to produce more chemically stable constituents; and
Solidification - involves the addition of reagents to a contaminated material to impart physical/dimensional stability to contain contaminants in a solid product and reduce access by external agents (e.g. air, rainfall).

In situ oxidation

New in situ oxidation technologies have become popular, for remediation of a wide range of soil and groundwater contaminants. Remediation by chemical oxidation involves the injection of strong oxidants such as hydrogen peroxide, ozone gas, potassium permanganate or persulfates. Oxygen gas or ambient air can also be injected to promote growth of aerobic bacteria which accelerate natural attenuation of organic contaminants.

Biological Treatments

Biodegradation generally refers to the breakdown of organic compounds by living organisms eventually resulting in the formation of carbon dioxide and water or methane. Inorganic compounds are not biodegraded, but they can be biotransformed, that is, transformed into compounds having more or less mobility or toxicity than their original form. In many cases, the biodegradation processes involve a particular microorganism that attacks a specific molecular site. Complete and rapid biodegradation of many contaminants may require, not only specific environmental conditions, but also changing conditions to satisfy the needs of the microbes.

Cementitious Waste Forms.

Sulfur polymer cement (SPC) has been used to stabilize high loadings of volatilized toxic metals. SPC is a sulfur composite material with a melting point of 110-120° C, that resists attack by most acids and salts. Studies show that the compound has a very long life and its strength greatly increases within the first few years after forming.

Incineration Technologies

Several types of incinerators are reviewed, including: the rotary kiln, infrared furnaces, liquid injection, plasma arc, fluidized bed, and the multiple hearth. Hazardous wastes can be volatilized and combusted in incinerators at temperatures that range from 870 to 1,200° C. Incineration at these temperatures can break the chemical bonds of organic compounds and other substances. Incineration reduces the risks posed by hazardous wastes because they efficiently destroy chemical contaminants, thereby reducing the toxicity and volume of substances at hazardous waste sites. The toxicity of radioactive contaminants, however, would not be eliminated by incineration, although bulk volumes may be reduced.

Soil Washing.

Soil washing as a volume reduction process is relatively new. Early efforts concentrated on extraction using aqueous solutions and ignored the physical separation/volume reduction possibilities. The first stage of the process removes coarse soil (known as physical washing) and then relies on a multiple- stage chemical extraction process for washing contaminants from the fine (< 2 mm) soil. Soil surfactant washing refers to the treatment of excavated soil or other matrix with a surfactant solution. Soil surfactant flushing, on the other hand, refers to a similar process, but with soils remaining in situ.