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Low-frequency Stratagem EH4 Used in Ground Water Exploration The Geometrics Stratagem EH4 has been used successfully in many countries for characterizing the geology of likely groundwater sites.  The following is an example of using the optional low-frequency capability of the Stratagem EH4 for hydrogeologic studies at depth.  The standard Stratagem EH4 operates in the frequency band of from 10 Hz to 100 kHz.  By using optional low-frequency magnetic sensors, low-frequency buffered electrodes, Cu/CuSO4 porous-pot  electrodes, longer electric dipoles, and low-frequency processing software the Stratagem frequency range can be extended down two additional decades to 0.1 Hz.

The depth section above was obtained by the Stratagem in Fu Ping, Shanxi Province, China.  The use of the low-frequency option allowed a depth of investigation to greater than 1 km.  This area of China is relatively arid and ground water is normally found in deep fractures.  The geology consists of Quarternary and Tertiary sediments over Ordovician limestone.  The Stratagem EH4 detected two fracture structures and a wall was drilled in fracture No. 1.  This resulted in a productive well in which water was found at 580 meters.  The daily water production is 13,300 m3, which is the most productive well in the area. The line was over 3 km long, and consisted of a continuous profile of 32 stations using 100-meter  dipoles.  Data was collected by the Stratagem EH4 and processed using he built-in Stratagem 2D analysis software.  The contour plot was done using Surfer™ from Golden Software. Geometrics thanks the Chinese  "Hydrogeological and Engineering Geological Technical Research Institute, Ministry of Geology and Mineral Resources" for the use of this data.