EM31, EM34, EM39, EM61 Methods
Purpose: The EM (Electromagnetic) methods, using Geonics instruments like EM31, EM34, EM39, and EM61, are crucial for detecting and mapping subsurface features. These methods excel in environmental surveys, identifying buried metal, soil contamination, utilities, and other geotechnical targets.
Applications:
Shallow Subsurface Mapping (EM31): EM31, commonly used in vertical dipole mode, provides shallow penetration (up to 6 meters) and is ideal for locating pipes, buried structures, and landfill extents.
Deeper Investigations (EM34): EM34 reaches greater depths (up to 60 meters with specific configurations) and is suited for detecting geological changes and contamination across larger areas.
Environmental Analysis (EM39): Borehole-specific EM39 with conductivity and gamma probes is valuable for environmental studies, distinguishing clean, contaminated, and clay-rich soils based on conductivity and gamma responses.
Technical Process: These methods use various dipole configurations and coil separations to adjust penetration depth. Data is processed into color-contour maps of conductivity and inphase values, revealing subsurface variations. The EM39 borehole tool specifically provides depth-specific data, enhancing contamination assessment.
Key Uses: EM31, EM34, EM39, and EM61 methods collectively offer flexibility in depth and resolution, making them effective for environmental assessments, construction planning, and utility mapping across a wide range of depths.
- The Geonics EM31 geophysical method is industry standard and most commonly used in the ‘vertical dipoles mode’ for penetration up to approximately 6 metres deep.
- The apparent conductivity and inphase results present as colour-contour plan maps. The inphase, when interpreted with the corresponding apparent conductivity response, are useful for detecting buried metal, fill, former structures, pipes/utilities, slag, landfill extents, etc.
- EM31 results combine with EM34 results for deeper penetration and pseudo-depth sections,
EM31 Horizontal dipoles | Penetration Depth 3m | Plot-point Depth 2m
EM31 Vertical dipoles | Penetration Depth 6m | Plot-point Depth 4.5m
EM34 Horizontal dipoles, 10m coil separation | Penetration Depth 7.5m | Plot-point Depth 5m
EM34 Horizontal dipoles, 20m coil separation | Penetration Depth 15m | Plot-point Depth 10m
EM34 Vertical dipoles, 10m coil separation | Penetration Depth 15m | Plot-point Depth 11.25m
EM34 Horizontal dipoles, 40m coil separation | Penetration Depth 30m | Plot-point Depth 20m
EM34 Vertical dipoles, 20m coil separation | Penetration Depth 30m | Plot-point Depth 22.5m
EM34 Vertical dipoles, 40m coil separation | Penetration Depth 60m | Plot-point Depth 45m
- EM39 borehole surveys typically consist of a conductivity probe and a gamma probe
- This combination is useful for environmental investigations
- Clean sandy soils typically have low gamma counts and low conductivity values.
- Contaminated soils typically have high conductivity while the gamma counts remain unchanged.
- Clayey soils typically have high gamma counts and high conductivity.
- See also:
