Case Histories of Shallow Time Domain Electromagnetics in Environmental Site Assessment

Abstract

Time domain electromagnetic (TDEM) soundings were utilized in site assessment studies for the purpose of accomplishing two objectives: (1) measuring the migration of brines from oil and gas field evaporation pits, and (2) mapping the continuity of clay strata. Both case histories are representative of common objectives in site assessment. The data for both examples were analyzed by one‐dimensional ridge regression inversions. Both case histories illustrate that TDEM is an effective method for determining the lateral and vertical resistivity distribution (geoelectric section) of the subsurface in the depth range from about 5 m to 100 m, and it is known from other investigations that depths of investigations up to 2500 m can be achieved with TDEM. Frequently, the lateral extent of contaminant plumes emanating from localized sources are of limited areal extent. The case history involving the use of TDEM to map a brine plume shows that a TDEM measurement has a relatively small zone of influence, so that meaningful information about the lateral and vertical extent of the plume can be obtained. Both case histories demonstrate the ability of TDEM to determine geoelectric sections below layers of low resistivity.

Joint full-waveform analysis of off-ground zero-offset ground penetrating radar and electromagnetic induction synthetic data for estimating soil electrical properties

“…This method operates at frequencies ranging from 1–100 kHz. EMI applications are quite diversified, it is notably used for salinity mapping and monitoring in agricultural fields (Cameron et al 1981; Hendrickx et al 1992; Lesch et al 1998; Amezketa 2006), soil water content estimation (Kachanoski et al 1988; Reedy & Scanlon 2003; Sherlock & McDonnell 2003), soil texture mapping (Hedley et al 2004; Triantafilis & Lesch 2005), soil acidity assessment (Dunn & Beecher 2007), detection of buried metallic bodies like unexploded ordnance (UXO) (Pasion et al 2007; Huang & Won 2003), detection of contaminants in soils and shallow aquifers (Ladwig 1983; Hoekstra et al 1992), clay content estimation (McBratney et al 2005; Triantafilis & Lesch 2005) and characterization of the vadose zone (Everett et al 2006).…”

An Electromagnetic Induction Survey of a Riparian Area in Southwest Montana

“…Though seldom diagnostic in themselves, lateral and vertical variations in apparent conductivity have been used to infer changes in soils and soil properties. Spatial patterns of apparent conductivity have been used to guide sampling, assess the variability of soils and soil properties, construct soil maps, and facilitate site assessments (Hoekstra et al, 1992; Jaynes et al, 1993; Doolittle et al, 1996). Sheets and others (1994) used EMI to assess the suitability of saline riparian areas in central New Mexico for restoration.…”

Reconnaissance Soil Mapping of a Small Watershed Using Electromagnetic Induction and Global Positioning System Techniques

“…Apparent conductivity values are seldom diagnostic in themselves. However, lateral and vertical variations in these measurements can be used to infer changes in soils and soil properties (Corwin and Rhoades, 1982, 1990; Hoekstra et al, 1992; Jaynes et al, 1993; Kachanoski et al, 1988; Zalasiewicz et al, 1985).…”