Determining Location and Extent of Landfill

Aim

A combined geophysical and geotechnical strategy was adopted. Electrical Resistivity Tomography (ERT) was used to image the subsurface and delineate landfill material from surrounding soils, while Multi-channel Analysis of Surface Waves (MASW) provided complementary information on stiffness variations with depth.

Survey lines were carefully planned to maximise coverage within the site’s spatial constraints, and to integrate directly with invasive geotechnical boreholes. This approach ensured the investigations stayed on schedule and within budget, while extracting maximum value from each test.

Approach

An Electrical Resistivity Tomography (ERT) survey and a Multi-channel Analysis of Surface Waves (MASW) survey were undertaken. Due to the spatial constraints at the site, the survey lines were chosen to maximise the area covered and to integrate with the invasive geotechnical tests, all while working within the required time frame and budget.

Results

• ERT layout and integration: The below figure shows the ERT survey grid alongside borehole locations, with a contour map indicating variable landfill depth. The landfill extended to more than 5 m below ground level in places.

• Subsurface layering: Dimensional ERT profiles clearly distinguished the landfill as a low-resistivity zone within the top 5 m, underlain by a sandy gravel layer with higher resistivity.

• Ground model: The combined dataset provided a reliable subsurface model, clarifying the landfill boundaries and thickness, and highlighting zones with higher potential for leachate migration.

  
  

Outputs & Value

The integrated geophysical–geotechnical investigation delivered a clear picture of landfill extent and volume, reducing uncertainty and project risk.

• Risk reduction: Developers and councils gained early clarity on subsurface conditions, avoiding surprises during construction.

  
  

• Cost savings: By targeting invasive testing where it was most needed, the number of boreholes was reduced, lowering investigation costs.

  
  

• Environmental management: The ability to identify potential leachate pathways supported proactive planning and compliance with regulatory requirements.

  
  

The combined approach provided the client with a reliable ground model that de-risked the project, saved costs, and supported better long-term land management.