Soil remediation or soil washing is the process that removes contaminants or pollutants from the polluted soil. It is a water-based process of flushing the affected soil with chemical additives in other to maintain the natural balance of soil nutrients required for optimal plant growth. Badly affected soil may need to undergo remediation before the application of soil amendments treatment of any kind. It’s performed on brownfield sites, where chemical spills, runoff, or other environmental hazards have made the site unsuitable for other purposes, whether industrial, commercial, or residential. 

In this article, we will discuss how we can make the unsuitable site suitable by using different techniques.

We follow different techniques for soil remediation and these techniques can be divided into four types below.

Thermal/Heat Soil Remediation

Heat or thermal soil remediation is a process that essentially bakes the hydrocarbon in high temperatures. Typically, this method occurs in an oven, fed by a conveyor belt.

The hydrocarbon compounds such as oil or other petroleum products heated in order to force the contaminants to evaporate so that they can be collected. 

The heat of thermal soil remediation can be introduced to the subsurface by electrical resistance heating, radio frequency heating, dynamic underground stripping, thermal conduction, vitrification, injection of hot water, air or steam.

The treated soil is then cooled and pulled out from the remediation oven. After the procedure is done, the soil is then ready for recycling or further testing.

This technique is great for clays or moist soils that have trapped oil and other pollutants

Encapsulation

Encapsulation is the process of soil remediation that involves mixing cement, concrete, and lime into the contaminated soil, thus preventing the pollutants from leaching out. This process is also known as solidification and stabilization with cement. 

Encapsulating contaminated material can be a great technology for isolating contaminants and perhaps a suitable alternative for ensuring human wellbeing and environment when removal and off-site disposal may not be cost-effective and practical. 

Air Sparging

Air sparging involves the injection of pressurized air into the soil, thus disrupting and removing volatile organic compounds (VOCs). In air sparging, huge volumes of air are infused into a polluted soil stratum to constrain the organic vapors outwards where they are typically treated by carbon filtering. The actual time the process takes in treatment relies on various factors, for example, depth of the hydrocarbon pollution, the concentration level of contaminating, pH factors of the soil, and permeability of the soil. 

Air sparging is one of the most common methods of in situ remediations, so this is something to consider when looking at a soil remediation method.

Bioremediation

Bioremediation uses engineered aerobic and anaerobic bacteria that feed on the contaminants. After they’ve finished, they die off. This is considered a much more sustainable method of remediation, but it does require certain temperatures and climate.

The methods are site remediation and soil treatment are numerous with new techniques and technologies being developed all the time.

The process of bioremediation is basically two types: 

1. In-situ bioremediation
2. Ex-situ bioremediation

In-situ bioremediation: In this method, the bioremediation come about in the subsurface like the groundwater or soil. Some benefits of this type are lower costs, total elimination of the contaminants, and fewer risk factors to those around it. This is also less harmful with limited human involvement. That said, the surrounding environment can affect the ability to transform hazardous materials, and it has to be monitored nearly and consistently.

Ex-situ bioremediation: An alternative to in-situ, this method puts the tainted soil in the above-ground treatment area and eliminates contaminants using the indigenous microbial population. The outcome is ideal water and carbon dioxide. Oxygen is a very important part of this method as it is key to the growth of the good bacteria, so the excavation methods are therefore that much more significant. This method has proven time and again to be constructive but is not as adaptable as it may not work on certain metals and soils.

Soil remediation cost

With the standardization of soil analysis and improvement of remediation techniques, brownfield assessment and subsequent remediation are now more affordable than they were. Cost for site characterization can range anywhere from $1,500 for a small site up to the millions of dollars for large and complicated sites.

The treatment options are more expensive, ranging from $50,000 to $250,000 per acre for sites where the contamination only reaches down one foot. Careful cost analysis must be performed to determine if subsequent development on a cleaned site would be economically worth the remediation investment.

Conclusion

Advancements in science and technology have made brownfield cleanup more viable and affordable. In general, a robust analysis must be performed to determine both the appropriate remediation technique and the economic impact of performing the soil remediation.

Posted by:- M Mahmood

Edward Bertrand