The need to redevelop brownfield land for construction purpose led to develop several contamination treatment methods. These techniques of brownfield contamination treatment will be discussed in the following sections.
Techniques to Treat Contamination of Brownfield Land for Construction
- Excavation and refilling method
- Stabilization or solidification technique
- Vertical containment barrier
- Grouting method
- Cover layers
- Leaching and washing technique
- Chemical treatment
- Soil vapor extraction or air sparging
- Groundwater treatment
- Thermal processes
1. Excavation and Refilling Method
This technique is broadly used to treat contamination of brownfield land. The method involves the removal of contaminated soil and dumps it into landfill. Then suitable materials will be placed and compacted in thin layer for filled material to have satisfactory strength and withstand imposed loads. An outstanding factor that may restrict the utilization of such technique is its high cost.
Fig.1: Excavation and refilling method
2. Stabilization or Solidification Technique
This technique is used to treat heavy metals and organic contaminants. Binding mixtures are inserted into the ground using pressure injection or soil mixing augurs.
This technique will prevent mobilization of contamination by solidifying into a matrix that resists leaching. Lastly, the effectiveness of this method is dependent on the physical properties.
Fig.2: Solidification and stabilization technique to treat contamination of brownfield land
3. Vertical Containment Barrier
Vertical containment barrier is constructed using sheet pile wall, grouting, slurry trench wall, or soil mixing. The barrier will contain the contaminant and prevent its movement. The limitation of vertical containment barrier is the achievement of high impermeability.
Fig.3: Containment of contamination in brownfield land
4. Grouting Method
It can be used to control wide ranges of contaminant types. Commonly, pumpable materials are injected into the ground to improve strength, stiffness, density, infill cavities, and decline permeability of the ground.
The only disadvantage of grouting technique is that the flow of the grout cannot be controlled.
5. Cover Layers
A layer or several layer of filled and geo-synthetic material will be used to cover contaminants. This will reduce the movement of contaminated elements.
The limitation of this technique is that surface clay might dry out and consequently permeability will increase.
Fig.4: Using covering layers to treat contamination in brownfield land
6. Leaching and Washing Technique
This method is suitable only for above ground level water. Contaminant is removed in solution by leaching and in suspension or by washing. It can be employed to remove broad ranges of contaminants which are carried or mobilized by liquids.
7. Chemical Treatment
In this method, chemical agents are injected into the ground through trenches for shallow depth and wells for greater depth to destroy contaminants such as pesticides, fuels, and solvents. The only limitation of chemical treatment is that it might affect fauna and flora.
8. Soil Vapor Extraction or Air Sparging
Initially, vaporous contaminants are eliminated and then contaminated liquid will be treated. In this technique, contaminants that can be carried by vapor can be disposed. Soil vapor extraction method is applicable for sandy soil and it is used for volatile or partially volatile contaminants.
Fig.5: Soil vapor extraction used to treat contamination in brownfield land
9. Groundwater Treatment
As it may be noticed from the name, this technique is used for treatment of contaminated groundwater which is extracted and treated above the ground.
The application of this method is based on the hydrological and geological conditions.
10. Thermal Processes
In this method, water and organic contaminants are volatilized under 150 degree heating. Added to that, higher degree heating may be used to vitrify contaminant materials. Thermal process will remove or immobilize contaminants. This method may need dewatering that might restrict its utilization.
This method is used for organic contaminants only, cannot be used for inorganic contaminant. Certain types of fungi or bacteria, which are placed into ground, will destroy and transform organic contaminants by natural process of micro organisms.