Guideline Geo´s wide range of geophysical investigation techniques can solve most of the common questions regarding groundwater contamination and salination. They will provide a non-destructive and cost-efficient way of gaining a better understanding of the ground conditions, supplying better data coverage than is normally achieved with traditional, discrete, point-by-point geotechnical investigations and sampling, such as drilling or digging.
For groundwater applications in general it is necessary to use a physical property that can distinguish water from surrounding geologies, regardless of whether the water is found in unconsolidated materials (e.g. gravel, sand or silt), in rock fractures or in water-bearing permeable rock. Preferably it should also be possible to give information about the geological structures and layers. For contaminants and salination studies the method needs to be able to detect the difference between fresh and potentially hazardous water. As some aquifers can be found very deep, the geophysical method should preferably be able to ‘reach’ depths of 200 – 300 meters or maybe even deeper.
Guideline Geo provide efficient resistivity and TEM instrumentation, both very capable of mapping a physical property associated with the presence of contaminants and salination, a change of resistivity.
Typically, water has a low electrical resistivity, and thus most materials in which water is present will experience a change in resistivity from its original value. The more saturated with water a material is, the more its resistivity will change. Add to this the fact that salt has very low electrical resistivity, we can deduce that the higher the ion content of water, the lower the resistivity. This makes it possible to detect the difference between fresh water and saline water. If water is contaminated with a pollutant, in most cases its electrical properties will also change. Exactly how it will change depends on the pollutant but typically it will lower the resistivity due to an increased amount of dissolved ions.
Resistivity and TEM measurements are most often used as part of a single investigation, identifying anomalous regions at a particular moment in time, but they are also very suitable for monitoring or time-lapse measurements. To be able to track the distribution and pace of leachate spreading around a landfill area, is an incredibly powerful tool.
Note! All ABEM resistivity equipment is capable of also recording the chargeability of the ground (how quickly it charges up and subsequently discharges with the application and removal of current) using time domain induced polarisation methods. This additional dataset can be very useful in mapping different types of waste in a landfill, or interpretation of targets such as mineral deposits and clays.
Guideline Geo also provide GPR and seismic solutions, which can be beneficial for ground investigations relating to the mapping of contaminants or salination.
GPR can be used to map the bedrock topography (in other words pathways for groundwater and contaminants), the extent of protective clay layers, the thickness of friction soils etc. In some cases GPR can also be used to map the groundwater table, but this is limited to coarse grained soils.
The seismic method is most commonly used for measure depth to bedrock, bedrock quality, soil stability or mapping of geological structures. But depending on the aquifer type it can in some situations be easy to detect the groundwater table. The porosity and water saturation decides if seismics will resolve a groundwater surface. Seismics will not be able to differentiate fresh water from salt water or polluted water.