Montezuma Wetland Brines Results

Laura Sherrod - 2013

Due to the contrast between the moderate resistivity of the glacial sediments saturated in fresh water (approximately 10-100 ohm*m) and the very low resistivity of glacial sediments saturated in brines (less than 1 ohm*m), the subsurface brines are clearly visible as low resistivity (blue) anomalies in the resistivity profiles.  The image to the right shows the resistivity results of three 155m sections of the 2km east-west transect, with the western most survey (top) showing relatively high resistivity compared to the eastern most survey (bottom).  Combining these results with those from the north-south resistivity transect, it is apparent that the brines are prominent in the east and north of the area surveyed.  Boreholes located within the lines of the geophysical surveys indicate that the brines are found primarily in fine to medium sands.

Resistivity of the east-west transect from west (top) to east (bottom)

  GPR results of the east-west transect corresponding to the western (top) and eastern (bottom) resistivity surveys.  The image to the left shows two examples of the GPR results compared with the resistivity profiles.  The depth of the resistivity profiles (approximately 25m) is much greater than the depth of the GPR profiles (approximately 3m for the 200MHz antenna).  As the surveys were performed on dirt roads built in the wetland, the upper two meters of the GPR profiles show the fill material of the roads.  Results from the 200MHz GPR antenna were better quality than the 100MHz results due to the shallower depth of penetration for the higher frequency antenna.  However, these 200MHz profiles were not useful for identifying brines as the image was focused within the fill material instead of in the lower resistivity glacial deposits.  Overall, the results of the GPR surveys at the Montezuma Wetlands site show an attenuated image of the subsurface structures due to the high electrical conductivity of the subsurface. 
Sebastien Treciak and Brandon pull the 100MHz GPR antenna. Emily Snyder sits in the back of the field vehicle to monitor the GPR data collection. Emily Snyder, Alex Spielman, and Sebastien Treciak stop for a lunch break. 
Emily Snyder, Alex Spielman, and Sebastien Treciak lay a resistivity survey line.  Snails on the resistivity line - much better field work companions than the mosquitoes. Sebastien Treciak lays a resistivity survey line. 
Montezuma Wetland Brines
Geologic Mapping Ground Penetrating Radar
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