In-Situ Contaminant Mapping and Site Characterization using Ground Penetrating Radar (GPR)Technology SummaryEnviScan technology is based on indirect measurement of changes in soil conductivity using Ground Penetrating radar (GPR). Radar waves are reflected differently based on soil conductivity and moisture content. Changes in soil conductivity can be interpreted as an indication for soil contamination when calibrated to actual contamination levels based on a limited number of borings. After calibration of the readings, the radar data can be correlated to contamination levels to provide a 3-D image of the in-situ contamination. The method is highly sensitive and can be used to detect mineral oil, Hydrocarbon, creosote (PAH). BTEX, SVOC, VOC, NAPL, DNAPL in subsurface soils and/or ground water. Main features of the EnviScan technology are as follows: Case StudiesClick here for CASE STUDIES Prior to fieldwork, a site specific survey plan is prepared based and a grid is marked out on the location, in order to come to an accurate positioning of the radar measurements. Continuous recording lines are run along the grid with radar. The distance between the recording lines depends on the accuracy and precision required. Normally recording lines are run in X-direction, as well as in Y-direction at 7 feet spacing. GPS (Global Positioning System) is used for positioning the measurements in larger survey areas. Under ideal circumstances (homogeneous sandy soil) the maximum survey depth is about 50 feet below ground surface. The measurements are non-destructive; it is possible to measure through hard spots. Metal objects, such as wells, pipes, cables and concrete reinforcement can provide disturbances in the radar data. To filter out these disturbances, a correction to the data is applied. It is not possible to locate soil contamination in places where tanks or clusters of pipes are present below ground surface.
After the fieldwork has been carried out the accumulated data are processed and analyzed. As results, a 3-D image is developed of the expected relative soil contamination levels as function of depth. When radar readings are "calibrated " to actual contaminant levels as determined by (limited) boring data, the 3-D image of relative contaminant levels can be converted to a 3-D image with expected contaminant concentration levels. The maximum detectable values of contamination are dependent on local conditions and contaminant of concern. For Organochlorinated compounds, detection levels can be in the low part-per-million (ppm) levels for soil and ground water, whereas for mineral oil detection levels are typically in the range of 200 to 500 ppm in soil and in the range of 10 to 50 mg/l in ground water. |
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