Groundwater Geophysics

Geophysical techniques are used to assist both groundwater resource and environmental assessments. Geophysics can provide a cost-effective means of extending or leveraging data obtained using costly intrusive sampling techniques such as drilling or excavation.

CMJA uses geophysical techniques where appropriate in both resource and contamination investigations, and is a member of the Environmental and Engineering Geophysics Society.

DC resistivity sounding is used to obtain information concerning the layered vertical profile beneath a site. Vertical changes in lithology, saturation and groundwater salinity can be assessed. However, due to the ambiguities inherent in the method, some control derived from borehole data or another geophysical method is necessary.

Frequency-domain electromagnetic techniques using equipment such as the Geonics EM34-3 and EM31 can be used to rapidly measure lateral changes in the electrical conductivity of the ground without the need for ground-contact electrodes.

Examples of the use of this technique include:

Mapping of sand lenses beneath areas proposed for effluent irrigation and water storage in western NSW and Victoria - EM34
Mapping of contaminant plume from leaking effluent storage lagoons - EM34
Groundwater exploration in shallow river gravels - EM31
Searching for buried drums, pipes and tanks - EM3

Other geophysical techniques used by the company include borehole logging, used to obtain precise definition of formation boundaries and salinity changes, and time-domain electromagnetic sounding, used in a similar way to DC resistivity sounding, but providing better spatial resolution and better contract in low-resistivity environments.