Geophysical methods are indirect methods of investigation of subsurface structures through the acquisition and interpretation of instrumental data , therefore , characterized as non-invasive or non-destructive methods .This methodology allows to evaluate the local geological conditions through contrast of physical properties of the subsurface materials , eg conductivity or resistivity , dielectric permittivity , magnetism , density , etc. Which may originate as the lithological differences and other natural heterogeneities or not.
One of the main advantages of the application of geophysical techniques over traditional methods of subsurface investigation , eg , surveys , is the rapid evaluation of large areas with relatively lower cost . In addition, geophysical surveys provide continuous running profiles , allowing a more precise identification of the lateral lithological variations resulting from or arising out of the presence of groundwater contamination changes.
In the environmental assessment of contaminated areas , conducting geophysical surveys has the basic objective identification of the presence of groundwater contamination and the definition of the geological and hydrogeological features of the investigated sites .The characteristics of the geological environment , and the nature of the contamination, can determine the behavior of contaminants in the subsurface.
In this context , the interpretation of geophysical data can contribute to obtaining information about the lithology , stratigraphy , depth of water table , depth of the foundation , presence of faults or fractures , there are important aquifers , groundwater preferred propagation paths and other geological features of interest .In assessing the presence of contamination in depth , the use of geophysical methods is geared specifically to the location of ditches containing waste , investigation of widespread contamination in soil and groundwater , detection of buried drums and tanks and determination of leaks in tanks or ducts.
The application of two or more distinct geophysical methods increases the accuracy of interpretations , and the nature of the contaminant and the local geology are decisive in the selection of geophysical techniques to be used factors .Significant deviations from the normal pattern of geophysical measurements , which are the abnormalities , may, from the environmental point of view, point to the presence of contaminants in the subsurface . The interpretation of the anomalies is critical as it can indicate the intensity of this contamination , thus providing important activities for diagnostic , monitoring the spread of contaminants and monitoring the recovery of a contaminated area data.
Thus , the information derived from geophysical surveys are useful for locating the monitoring wells , but can also provide estimates of area and volume for the activities of removal and remediation of contaminated soils . Moreover, they can be applied to reduce the risk of drilling tanks and buried drums containing waste , or pipelines and underground galleries.
Source: Geoanalysis blog