ASTM International

Standard Guide for Use of the Time Domain Electromagnetic Method for Subsurface Investigation
 N D6820

Annotation

Purpose and Application—This guide summarizes the equipment, field procedures, and interpretation methods for the assessment of subsurface materials and their pore fluids using the Time Domain Electromagnetic (TDEM) method. This method is also known as the Transient Electromagnetic Method (TEM), and in this guide is referred to as the TDEM/TEM method. Time Domain and Transient refer to the measurement of a time-varying induced electromagnetic field.

The TDEM/TEM method is applicable to investigation of a wide range of subsurface conditions. TDEM/TEM methods measure variations in the electrical resistivity (or the reciprocal, the electrical conductivity) of the subsurface soil or rock caused by both lateral and vertical variations in various physical properties of the soil or rock. By measuring both lateral and vertical changes in resistivity, variations in subsurface conditions can be determined.

Electromagnetic measurements of resistivity as described in this guide are applied in geologic studies, geotechnical studies, hydrologic investigations, and for mapping subsurface conditions at waste disposal sites (1).2 Resistivity measurements can be used to map geologic changes such as lithology, geological structure, fractures, stratigraphy, and depth to bedrock. In addition, measurement of resistivity can be applied to hydrologic investigations such as the depth to water table, depth to aquitard, presence of coastal or inland ground water salinity, and for the direct exploration for ground water.

General references for the use of the method are McNeill (2), Kearey and Brooks (3), and Telford et al (4).

Limitations:

This guide provides an overview of the TDEM/TEM method. It does not provide or address the details of the theory, field procedures, or interpretation of the data. Numerous references are included for that purpose and are considered an essential part of this guide. It is recommended that the user of the TDEM/TEM method be familiar with the references cited and with the ASTM standards D 420, D 653, D 5088, D 5608, D 5730, D 5753, D 6235, D 6429 and D 6431.