Military Hydrology. Report 10. Assessment and Field Examples of Continuous Wave Electromagnetic Surveying for Ground Water

A CW EM system was field tested at White Sands, NM, and Fort Carson, CO at locations where previous geophysical surveys were conducted using seismic and electrical resistivity methods. For the White Sands EM surveys, a critical evaluation of data interpretation procedures is presented. The EM interpretations are compared to models deduced from the previous geophysical work at the locations. At Fort Carson, an EM sounding was conducted at 20-m intervals along a 700-m profile line. An EM sounding was also conducted on Dakota Sandstone outcrop. The EM device evaluated in this study is lightweight and easy to operate in the field; surveys proceed rapidly. These comments apply in general to Cw EM systems. the device considered in this report could not 'stand alone' nor replace electric resistivity in a complementary methods approach for ground-water detection and assessment; however, it can be useful as a rapid survey technique to supplement resistivity surveys in a complementary methods approach. CW Em methods are not limited to the small number of conductivity determinations (coil spacing-frequency combinations) of this device. Currently available CW EM systems with greater capability and applicability, however, are larger and more cumbersome to use, and data interpretation is not as straightforward. See also Report 13, AD-A170 641.