EM-31 Survey, EM-61 Survey, and EM-34 Survey
(Click to enlarge)
Extent of plume
Site Characterization Surveys
With the recent brownfields legislation, accurate and rapid site characterization is an important factor in the site assessment process. An important aspect of site characterization is investigation of the subsurface soil, rock, and groundwater.
Several non-destructive field surveys can provide subsurface information that can assist with site characterization without digging, probing, or drilling. These non-destructive subsurface investigation surveys can rapidly delineate variations in the subsurface conditions that may influence migration of contaminants on the site.
The first type of non-destructive field survey usually conducted in site characterization at brownfields sites is an electromagnetic conductivity (EM) or terrain conductivity survey. This survey can be conducted very quickly and a map showing high or low conductivity areas (possible contamination) and areas of buried metal are quickly determined. The pictures and map below show how an EM survey is conducted and the results that are obtained.
EM-31 Survey, EM-61 Survey, and EM-34 Survey
(Click to enlarge)Extent of plume
For more information about the non-destructive survey method of electromagnetic conductivity Click Here
The second non-destructive field survey typically conducted for site characterization at brownfields and other sites and facilities is a ground penetrating radar (GPR) survey. A GPR survey can be conducted over the entire area of site characterization or only in those areas where a previous EM survey showed anomalous conditions. The GPR survey shows cross sectional information in pictorial form. The pictures and image below show how a GPR survey is conducted and the results that can be obtained.
Hand-towed GPR survey and truck-towed surveys
(Click on GPR images to enlarge)
For more information about the non-destructive survey method of ground penetrating radar Click Here
Another method for site characterization study may be required or desirable. A ground resistivity survey can be conducted to produce geoelectric sections at station locations, a generalized resistivity contour map, or a very detailed image of the subsurface to substantial depths even in clayey soils. The picture and image below show the resistivity equipment and the results that can be obtained.
Application of the surface resistivity method requires that an electrical current be injected into the ground by surface electrodes. The resulting potential field (voltage) is measured at the surface by a voltmeter between electrodes.
The apparent resistivity of the subsurface materials can be calculated by knowing the electrode spacing, geometry of the electrode positions, applied current, and measured voltage. The apparent resistivity values are entered into a computer program that calculates the geoelectric sections or columns for each sounding location, as shown in the images below. Surface resistivity measurements are reported in units of ohm-meters or ohm-feet.
The depth of the resistivity measurement is related to the spacings of the electrodes and may vary depending on the subsurface conditions. The surface resistivity unit has a self-contained transmitter, capable of obtaining data to about 50 to 100 meters (160 to 300 feet), using self-contained, rechargeable batteries.
For more information about the geophysical survey method of surface resistivity Click Here
GeoModel, Inc. conducts surveys in every state.
Contact us to check the availability of a crew in your state.
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e-mail:
geomodel@geomodel.com
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