Remediation of Metals – Contaminated Soils and Groundwater Research Paper

Situation 1- Remediation of PCBs in Sandy Soils Through Incineration

Polychlorinated biphenyls (PCBs) are deposited within the soils because of man made activities that are carried out on the soil surface depositing several harmful compounds. Their presence in the soil can have negative consequences for the environment, which can portend harmful environmental health for all plants and animals dependent on that ecosystem.

To counter the effects of these components within the soil, incineration technology has been chosen as one of the best remediation technologies for this pollution. This is because incineration can capture the contaminated soil deposits and PCB components and carry out the detoxification process away form the site the pollution has occurred¹.

Clean up by incineration takes place through desorption in situ of contaminated soils sediments by application of high thermal procedures, which enable the PCBs to be captured for destruction away from the site.

Through the use of In –Situ Thermal Desorption technology, the procedure is able to heat is applied directly within the contaminated soil and the organic contaminant is then destroyed because of the strong amounts of heat are able to destroy these harmful components².

The technology does not have adverse effects on the air quality surrounding the areas in which it is deployed and it is able to detect contamination in extensively deep soil deposits, which would be harder to detoxify by other technologies.

The technology has been found to be able to remove contaminants where contaminant molecules are destroyed in a highly vaporized facility and the only emissions from the process are in the form of oxygen and carbon dioxide.

The time that the remediation technology can take in cleaning up the soil sediments of the contaminants varies depending on the specifications and the rules that have been put in place meant to guide and supervise the incineration procedures to be adopted.

The set standards for incineration in soil environments with more that 50 pmm of PCBs has been set at 2 seconds residence time at a temperature of 1200 Celsius and 3% excess oxygen that is to be emitted once the vaporization has taken place³. The use this technology is encouraged more for vast areas of land because of the economies of scale it offers because of the high cost implication likely to be felt during its implementation.

The destruction of PCB contaminants by incineration has been found to be inefficient when compared to other non-combustible remediation technologies. Some incinerators are known to release harmful substances that may have been newly formed or undestroyed thereby polluting the environment that is surrounding.

The technology has been estimated to be able to clean up to 99.9% of the PCB contamination that exists within soil deposits where contaminations as high as 5000mg/kg have been found to exist. Some of these contaminations are between 6-18 inches in depth with a concentration of PCB’s being beyond 50ppm.

The technology is not very suitable for smaller sites and may have potential damages for underground infrastructure such as electrical cables and gas lines in the sites where it is used.

If the area to be treated is below the water table, there may be need to draw out the water first before the procedure can be undertaken. The thermal procedures undertaken can enable the undestroyed and newly formed contaminants to be released into the air and water resulting in poor environmental health⁴.

Situation 2- Remediation of Voc – TCA in Ground Water 20 Ft below Ground Level

Volatile organic Compounds are usually introduced to the unethical industrial practices which contaminate the quality of ground water that exists within a given environment. Trichloroethane compounds get absorbed into soil and ground water where they become contaminants, which can pose great risks to plant, animal and human life.

The remediation technology that is suitable for dealing with TCA contaminants within ground water is bioremediation, which makes it possible for the TCA contaminants to be biodegraded within the ground water through several processes.

The chlorinated solvents within the groundwater can be biodegraded through dechlorination, co metabolism and oxidation whereby all these processes deal with reducing the molecular components of the chlorine contaminants within the ground water⁵.

Biodegradation usually accelerates the dissolution rates of the chlorine solvent within ground water by transferring the dissolved substance to a collection point from which it can be drawn out.

Reducing dechlorination within the ground water structure is meant to replace the chlorine atoms that are prevalent within the ground water to a less toxic sate because they are replaced gradually with hydrogen molecules. Therefore, reductive dechlorination is the most favored form of biodegradation because it can dissolve the contaminants both within highly chlorinated and lowly chlorinated solvents⁶.

Since biodegrading involves high dechlorination of very toxic ground water conditions, it takes a shorter period when compared to the use of surfactant and co-solvent flushing. These conditions, therefore, make it suitable as a remediation technology to be deployed within underground water environments.

They are not very sensitive in densely contaminated environments where TCA is mostly prevalent making it suitable for cleaning up ground water areas, which have been severely exposed to TCA. The TCA within the ground water can then be dissolved and the toxicity within the ground water can be minimized.

The operational costs of the procedure are known to be low and in this situation, this can offer higher levels of efficiency because the procedure requires simple ground water extraction at low depths⁷.

Since the process can be easily combined with other technologies, there is a potentially higher rate of clean up, which can be achieved compared to other alternative types of technology.

The technology can be combined with the use of surfactants and co solvent flushing within the ground water table to accelerate the rate of cleaning up the ground water environment thus making its usage have a wider appeal. The procedure is effective in cleaning up large sections of contaminated areas within the ground water environment because of the fast rate at which cleaning up can be conducted⁸.

The major challenge that arises with the use of this technology is the negative impacts it can have on the quality of ground water within the earth’s crust.

The process may lead to the formation of metallic compounds such as iron, manganese and arsenic, which are very toxic and can create dangers for the water systems within these areas. The process requires very delicate handling because some electrons can be flammable and can create disasters if wrongly handled⁹.

Situation 3- Remediation of Pesticide- Arsenic in Groundwater through Precipitation

Arsenic components in ground water usually result from the effects of pesticides that are used to rid plants of pests, which after a while are absorbed and find their way to the water table.

Precipitation and co-precipitation is one of the technologies that have been used as a remediation for reducing the level of arsenic contamination in ground water because of its abilities to oxidize the arsenic components within ground water to a less soluble state.

This oxidation through ozonation and addition of other chemical components like potassium permanganate make it difficult for the arsenic to dissolve in ground water. This makes the arsenic to form become a solid precipitate making it easy for it to be filtered from the ground water leaving few traces of the contaminant within the water¹⁰.

The time taken for this technology to be effective in achieving its desired results varies from one site to the other depending on the level of contamination that exists. The pH at which the arsenic precipitate cannot be dissolved easily is the most effective one in determining the effectiveness of the technology that is used for precipitation of the arsenic contaminants in ground water.

Previous usage of this technology has shown that in one minute 65 gallons of ground water containing about 0.3mg/l could be detoxified.¹¹ The technology is estimated to be able to offer more benefits depending on the type of chemicals the user chooses to use to aid in cleaning up the ground water contamination.

It can be able to treat other contaminants, which are different from arsenic thereby giving it more appeal since it can be able to remove other pollutants unrelated to arsenic. It needs large expanse of land for it to be cost effective because of the high level of skilled labor that is required.

The technology is suitable in cleaning up highly contaminated arsenic ground water environments albeit on a large scale. The technology can be able to detoxify close to 0.3 mg/l of arsenic to water making it more preferable in dealing with the issue of ground water contamination when compared to other technologies.

The procedure is vital in detecting arsenic as well as other hard metallic components that are likely to be dissolved within ground water over a given period. In some instances, precipitation has been able to achieve arsenic amounts of about 0.05 mg/l but this largely depends on the pH adjustment adopted and the type of chemicals used¹².

This technology is appropriate for large-scale sites where the labor costs and other expenses can be used in large quantities for a positive outcome to be realized. The type of chemical oxidant to be used will invariably have a direct bearing on the costs of the procedure that is carried out.

The usage of precipitation procedures may not be enough to clean up all contaminants within the ground water especially if there are some additional components that cannot be extracted from the water table by the procedure. Process can also lead to hazardous waste being obtained in form of the arsenic solid precipitates and if poorly disposed of can have adverse consequences for the environment¹³.

Situation 4- In Situ Soil Flushing Remediation of Chromium & Mercury in Fertile Soil 4 Feet Deep

Chromium and mercury are some of the metallic components that contaminate arable soils thereby becoming part of the chemical make up of the crops that grow on this soil. These contaminants permeate into the soil horizon as a result of poor disposal methods of used batteries, cosmetics and cleaning agents.

In-situ soil flushing is the best technology that can used to minimize on the level of contamination of the two metallic components within the soil. It can be used to leach the components of chromium and mercury within the soil surface to ensure that they can be extracted without having to excavate the contaminated soil.

This makes it possible for the contaminants to be eliminated from the soil without having to carry out large-scale digging out of the soil, which may have more negative consequences for the contaminated site¹⁴.

This technology utilizes water, which is flushed into the contaminated area to move the contaminants so that they can be extracted easily without making the soil itself to move. In comparison to other technologies, is not effective if not used without surfactants because some of these contaminants may not be able to dissolve in water thereby increasing the costs borne by the user.

This flushing is done by flooding the surface using sprinklers or through vertically dug wells whereby water collects itself in the contaminated zones. In-situ technological procedures enhances pump and push procedures whereby the pushed water is able to dissolve the contaminants rapidly enabling a reduction of these pollutants within the soil quickly¹⁵.

In-situ soil flushing requires large quantities of water to push out the contaminants out of the soils in order to achieve the desired quality of cleaning up the contaminated soils. The usage of surfactants containing anionic chemicals to clean up contaminated soils yield better results than the usage of ionized water without any surfactants in performing the same function.

The degree of cleanup achieved especially if more surfactants are used is high because more contaminants can be washed away from the soil without having to excavate it. Several experiments carried out have shown that amounts close to 5,000 mg/l in ground water decreased to less than 50mg/l within the first two years of the introduction of water flushing procedures.

The amount of chromium concentration in ground water decreased from 1,923mg/l to 207 mg/l after approximately more than 3.8, million gallons of water had been used. These statistics show that the procedure is more effective in cleaning up toxins within the soil because when used with surfactants, soil flushing can remove more contaminants from the soil¹⁶.

The challenges that arise out of costs and the lack of technological know how make the usage of these technologies not to be easily accessible to many who may have a need for them.

The usage of chemical surfactants and the flushing systems that are required to be in place to aid their operation are likely to make the costs to be higher. Other costs related to designing an effective aquifer and the ways to dispose of the dissolved contaminants after flushing the contaminants must be carefully assessed.¹⁷

List of Bibliography

Evanko, Cynthia R. and David A. Dzombak. Remediation of Metals – Contaminated Soils and Groundwater. Pittsburgh: Carnegie Mellon University Department of Civil and Environmental Engineering, 1997.

Geosyntec Consultants GUELPH (Ontario), “Assessing the feasibility of DNAPL source zone remediation:: Review of case studies”. Report, Ontario, 2004.

Interstate technology and Regulatory Corporation Work Group, “Emerging Technologies for the Remediation of Metals in Soil”, Emerging Technology Project, New York, 1997.

“Technology Alternatives for the Remediation of Soils Contaminated with As, CD, CR, Hg and Publication”, Washington, DC : U.S. Environmental Protection Agency, Office of Emergency and Remedial Response, 1997.

Rahuman, Luigi and Stanisluv Ferruccio. Destruction Technologies Biphenyls. Unido Publications. Trestan: UNIDO, 2000.

United States Environmental Protection Agency. “Arsenic treatment Technologies for Soil, Waste and Water”, Report, USA, 2002. Web.

Footnotes

1. Luigi Rahuman, and Stanisluv Ferruccio. “Destruction Technologies Biphenyls”. Unido Publications. (Trestan: UNIDO, 2000), p. 11-13.
2. Ibid : page 14.
3. Ibid: page 15.
4. Ibid: page 15.
5. “Geosyntec Consultants, Assessing the feasibility of DNAPL source zone remediation: review of case studies” (report, Ontario, Canada, 2004), pp. 124- 126.
6. Ibid page 128-129.
7. Ibid; page 130.
8. Interstate technology and Regulatory Corporation Work Group, “Emerging Technologies for the Remediation of Metals in Soil”, (Emerging Technology Project, New York, 1997), p. 25-29.
9. Ibid: page 30-32.
10. United States Environmental Protection Agency. “Arsenic treatment Technologies for Soil, Waste and Water”, (report, USA, 2002), p. 90.
11. Ibid: page 92.
12. Ibid: page 13.
13. “Technology Alternatives for the Remediation of Soils Contaminated with As, CD, CR, Hg and Publication”, (Washington, DC : U.S. Environmental Protection Agency, Office of Emergency and Remedial Response, 1997), p. 14.
14. Ibid: page 4.
15. Cynthia R. Evanko and David A. Dzombak. Remediation of Metals – Contaminated Soils and Groundwater. (Pittsburgh: Carnegie Mellon University Department of Civil and Environmental Engineering, 1997), p. 7-10.
16. Ibid: page 28 -30.
17. Ibid: page 37-40.