Near Surface Geophysics

Alpha Geoscience.
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Introduction

Geophysics has been used extensively for near surface ‘targets’ with a high degree of success.

Targets	Techniques	Comments
Site Assessments	Ground Conductivity	Some environmental sites are extensive in nature and require assessment to highlight areas that could require more concentrated assessment. Geophysics provides tools to give a regional assessment to allow a more focused approach to environmental sampling.
Chemical Pollutants	Ground Conductivity Resistivity Survey	Generally an EM system would be used, however as each project is different in contamination, geology, surface topography and infrastructure, these all need to be assessed before a survey technique can be recommended.
Underground Storage Tanks	GPR Ground Conductivity EM61 TEM Survey Total Field Magnetics	The recommended technique will depend on the site conditions. On service station sites, GPR is eminently more suitable. However, on large open area sites, other techniques are more appropriate.
Underground Services Location	GPR Ground Conductivity EM61 TEM Survey Total Field Magnetics	One of the difficult problems on some environmental sites is the location of buried services, tanks and the like, which are not recorded on site maps.
Concrete Investigations	GPR	High frequency GPR is eminently suitable for the location of services, reinforcing bars, concrete failures, etc.
Rippability Investigations	Seismic Refraction	Before excavation is undertaken, rippability surveys can be undertaken to determine whether the site can be ripped with a bulldozer, or if there is need to use explosives.
Civil Engineering	Seismic Refraction Resistivity GPR	Geophysical tools can be used for geotechnical investigations including earth structures, ground hardness for excavation, position of services, etc. Alpha Geoscience has technical expertise in undertaking seismic refraction, resistivity and GPR surveys for civil engineering projects including road alignments.
Mine Engineering	Seismic Refraction Seismic Reflection Resistivity TDEM GPR	In mine engineering, geophysics can be used to assist in the location of zones of weakness, faulting, fracturing, rock stratigraphy and potential mine hazards.
Forensic Investigation	GPR Metal Detector EM61 TEM Survey Total Field Magnetics	Geophysics is eminently suitable for the location of a number of forensic targets that are sub surface. As geophysics is non-intrusive, it has no impact on the ground, thus leaving the site undisturbed. The depth of investigation will depend on a number of factors including size of the target, type of target and soil conditions, depth from near surface to tens of metres into the sub surface.
Buried Objects	Metal Detector (for shallow items) EM61 TEM Survey	Metal detectors are excellent for the location of buried metal objects in the top 0.5 to 1.0 metres of the ground, however they are not able to provide deeper investigations. Geophysics, with a number of tools, depending on the likely properties of the object, is very suitable for investigations to greater depth.
Grave Sites	GPR TDEM	As a human body has very similar properties to the soil, they are hard to locate directly, but the grave site edges will generally be the target for these surveys. The surrounding soil will be undisturbed and forms in layers, whereas the grave will be disturbed soil with sharp edges on either side. Conductivity mapping using TDEM may also allow for the identification of grave sites.
UXO	Total Field Magnetics EM61 Deep Metal Detector Ground Conductivity	UXO generally have a ferrous component to their body so can be located with magnetics. However in highly magnetic geologies, with small targets, it would be more advisable to use an EM system.