Electrical resistivity tomography of vadose water movement

Abstract

Cross borehole electrical resistivity tomography (ERT) was used to image the resistivity distribution before and during two infiltration experiments. In both cases water was introduced into the vadose zone, and the change in resistivity associated with the plume of wetted soil was imaged as a function of time. The primary purpose of this work was to study the capabilities and limitations of ERT to image underground structure and ground water movement in the vadose zone. A secondary goal was to learn specifics of unsaturated flow in a complex geologic setting. Tomographs of electrical resistivity taken before infiltration image coarser, well‐drained soils (sands and gravels) as more resistive zones, whereas finer grained soils (silts and clays), which hold more water by capillarity, are imaged as more conductive. Images of changes in resistivity during infiltration show growth of the water infiltration plume with time that is consistent with known geology. In the ERT images we see the effects of capillary barriers and infer differences between capillary‐driven flow through fine sediments and gravity‐driven flow through very permeable sediments. Images are consistent with numerical flow simulations using hydrological parameter values consistent with soil types inferred from well logs. ERT can be a useful tool to monitor movement of circuitous moisture fronts in a heterogeneous field setting that would go undetected by borehole measurements.

Vadose Zone Transport Field Study: Status Report

“…ERT has been demonstrated to be a useful characterization tool, providing details of the stratigraphy between wells (e.g., Newmark et al 1994), subsurface processes such as fluid infiltration (Daily et al 1992), and steam injection and ohmic heating (Ramirez et al 1993 by mapping the spatial and temporal changes in soil resistivity resulting from changes in liquid saturation and temperature. Since 2.8 tank wastes at Hanford were generally rich in high-ionic-strength electrolytes, resistivity could be an ideal surrogate for locating difficult-to-detect contaminants.…”

Multiscale electrical impedance tomography

“…Modern multielectrode data collection systems provide measurements with dense coverage [Asch and Morrison, 1989], and electrical impedance tomography is now currently used in hydrology [Bevc and Morrison, 1991;Daily et al, 1992;Park, 1998;Hagrey and Michaelsen, 1999;Nowroozi et al, 1999], environmental remediation [Van et al, 1991;Spies and Ellis, 1995;Daily and Ramirez, 2000], and spill monitoring [Ramirez et al, 1993]. Electrical impedance tomography is generally formulated as an inverse problem which aims at reconstructing the (possibly complex) electrical conductivity (or resistivity) distribution underground from electrical potential measurements made at the boundaries of the region to be imaged (see, for instance, Ward [1990] for a review).…”

Vadose zone transport field study: Detailed test plan for simulated leak tests

“…Electrical resistivity tomography (ERT) has been demonstrated to be a useful characterization tool, providing details of the Iithostratigraphy between wells (e.g., Newmark et al 1994), subsurface processes such as fluid infiltration (Daily et al 1992), and steam injection and ohmic heating (Ramirez et al 1993) by mapping the spatial and temporal changes in soil resistivity resulting from changes in liquid saturation and temperature. Because tank wastes at Hanford are generally rich in high ionic strength electrolytes, resistivity should be an ideal surrogate for locating difficult to detect contaminants.…”