Remediation of Contaminated Sites

Remediation of Contaminated Sites

By Dr. Yashpal Singh

The Ministry of Environment, Forest and Climate Change regards a contaminated site as a ‘delineated area consisting of aggregation of contaminated sources, the areas between contamination sources and areas that may contain contaminants due to migration from contamination sources.

A contaminated site may be determined so, if on investigation, the contaminants discharged are found to be located at the site in concentrations above the response levels and pose an imminent danger to life and property either on their own or in combination with other contaminants or between interactions with other contaminants.

A contaminant is defined as any substance that is potentially hazardous to human health or environment and is present in the environment in concentrations above its natural or back ground concentration.

While it is important to take adequate technical measures to prevent the ingress and penetration of hazardous substances from potentially contaminating activities, into soil, ground water or surface water, remediation of already contaminated sites is a major area of concern and needs appropriate attention. In the next couple of articles, we wish to discuss the technologies available for remediation of contaminated sites. Contaminated sites may include production areas, landfills, dumps, waste storage and treatment sites, mine tailing sites, spill sites, chemical waste handler and storage sites located in almost any land use area (residential, commercial, agricultural, recreational, industrial, rural, urban or wilderness).

Contamination can occur in soil, ground water or air trapped in soil generally regarded as the solid, liquid and gaseous phases of soil.

The Ministry of Environment, Forest and Climate Change in India has attached a conceptual importance to the fact that in case there is no contact between the contamination and the humans or the environment the contamination carries no risk.

(Although is felt that it may not be possible to avoid contact of a contaminant with the environment given the diverse edaphic and biotic inter relationships).

Remediation of contaminated site would have to decide if all contamination at all sites has to be removed or the decontamination could be limited to a certain acceptable level of risks at selected sites. The MoEF and CC suggests that for India, such anoptimum need to be found.

The source, pathway and receptor approach to risk assessment determines the possibility of a contaminant to come into contact with a receptor (Life or property) and the impacts are only considered detrimental if the contaminant comes into contact with the receptor through an identified pathway and that the presence of all three, source, pathway and receptor are important to establish this risk.

Remediation measures may need to be initiated if the site assessment demonstrates that the environment is at risk and the risks are unacceptable by prevailing law or perception of the stakeholders. This will then lead to the degree of decontamination required and the identification of remediation technologies.

The MoEF and CC, Government of India, lists the following fourteen steps in the site assessment and remediation process.

  1. Identification of probably contaminated sites.
  2. Preliminary investigation
  3. Notification of Polluted site.
  4. Priority list addition (ranking of sites based on threat perception)
  5. Remediation investigation involving site assessment and including risk assessment,fixing of targets and approaches.
  6. Remediation design involving the design of the selected remediation option, costing and planning.
  7. DPR approval and funding
  8. Implementation of Remediation
  9. Approval of completion of remediation including evaluation of remediation works.
  10. Post remediation plan including removal of residual contamination to meet and goals.
  11. Post remediation Action including periodical post remediation monitoring.
  12. Cost recovery from persons responsible for contamination.
  13. Priority List deletion
  14. Site reuse.

Depending on the characteristics of the contaminated site and the type of contaminant a number of remediation technologies can be generally used. These may include.

  1. Pump and Treat
  2. Air sparging combined by soil vacuum extraction
  3. Permeable reactive barrier
  4. Thermal Technologies
  5. Monitored natural attenuation for organic compounds
  6. In site flushing
  7. In situ oxidation/reduction
  8. Use of reactive zones.

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