Landfill mapping is the process of creating a detailed map of a landfill site to identify the location, extent, and nature of the waste deposited at the site. Geophysical techniques are often used for landfill mapping because they can provide a non-invasive and cost-effective way to detect and characterize buried waste.

Here are some of the most common geophysical techniques used for landfill mapping:

1. Ground Penetrating Radar (GPR): GPR is a non-invasive geophysical method that uses radar waves to investigate the subsurface of the landfill site. By sending electromagnetic waves into the ground and measuring the reflections that bounce back from different layers, GPR can identify the location of buried waste, estimate the thickness of waste layers, and detect voids and other subsurface features.

2. ERT (Electrical Resistivity Tomography) is a geophysical technique used for landfill delineation because it can provide detailed information about the subsurface electrical properties of the landfill and surrounding soils.

When waste is buried in a landfill, it can have a different electrical resistivity than the surrounding soil and rock. This difference in electrical resistivity can be detected using ERT. By measuring the electrical resistivity at different points around the landfill site using a network of electrodes, ERT can create a two-dimensional or three-dimensional image of the subsurface electrical resistivity distribution.

The electrical resistivity image generated by ERT can help to delineate the extent and boundaries of the landfill, as well as identify areas of low or high resistivity associated with the waste. ERT can also help to identify any void spaces or fractures within the landfill, which can be useful for planning remediation or expansion activities.

In addition, ERT can be used to monitor the migration of contaminants from the landfill into surrounding soils and groundwater. By periodically conducting ERT surveys, changes in the electrical resistivity distribution can be monitored and used to detect any changes in the migration of contaminants.

Overall, ERT is a useful tool for landfill delineation because it can provide a non-invasive, cost-effective, and efficient way to detect and map the extent and boundaries of the landfill, as well as identify areas of low or high resistivity associated with the waste.

3. Magnetic surveys: Magnetic surveys use a magnetometer to measure the magnetic field of the subsurface. Buried waste can cause a disturbance in the magnetic field, so magnetic surveys can be used to identify the location of buried waste.

4. Seismic surveys: Seismic surveys use sound waves to investigate the subsurface of the landfill site. By measuring the time it takes for the sound waves to bounce back from different layers, seismic surveys can create a detailed image of the subsurface geology and identify the location of buried waste.

Advantages of EMF techniques: 

1. Non-invasive: EMF techniques are non-invasive, which means they do not require drilling or coring. This reduces the impact on the landfill site and surrounding environment, while also making it possible to cover large areas quickly.

2. Quick data acquisition: EMF techniques are fast, and data can be acquired quickly. This makes it possible to survey large areas of landfill quickly and efficiently, which can be especially useful for time-sensitive projects.

3. Accurate data acquisition: EMF techniques can provide accurate data, which can be used to create detailed maps of landfill boundaries and areas of low or high resistivity. This information can be used to design remediation plans and manage landfill operations more effectively.

4. Real-time data processing: EMF techniques can provide real-time data processing, meaning that data can be processed and interpreted on-site. This can be useful for identifying potential areas of concern during fieldwork and making adjustments to the survey methodology as necessary.

5. Low cost: EMF techniques are relatively low-cost compared to other geophysical techniques. This makes it possible to conduct multiple surveys over time, providing valuable insights into how the landfill changes over time and allowing for more effective management and remediation.

Advantages of pulse techniques:

1. Greater depth penetration: Pulse techniques, such as ground-penetrating radar (GPR), can penetrate deeper into the subsurface compared to EMF techniques. This can be useful for mapping deeper areas of the landfill or identifying buried structures or objects.

2. High-resolution imaging: Pulse techniques can provide high-resolution images of the subsurface. This can be useful for identifying changes in soil density, structure, and composition.

3. Multi-frequency capabilities: Pulse techniques can operate at multiple frequencies, which can be useful for identifying different types of materials or objects buried in the landfill.

4. Low environmental impact: Pulse techniques are non-invasive and have a low environmental impact. This makes them a preferred option for environmentally sensitive areas.

In summary, both EMF and pulse techniques have advantages in landfill delineation. EMF techniques are quick, accurate, low-cost, and allow for real-time data processing, while pulse techniques can provide greater depth penetration, high-resolution imaging, multi-frequency capabilities, and have a low environmental impact. Depending on the specific needs of the project, one or both techniques may be used.

Geophysical techniques are used for landfill mapping because they can provide a non-invasive and cost-effective way to detect and characterize buried waste. This information is important for environmental management and monitoring, as it can help to identify potential environmental hazards and inform decisions about waste disposal and remediation.