USGS Home
Contact USGS
Search USGS

 Home  Resources  Research  Publications  About  Contact Us  Groundwater Information

Borehole radar tomography using saline tracer injections to image fluid flow in fractured rock*

By John W. Lane, Jr. **, David L. Wright, and F. Peter Haeni

Abstract

Cross-hole radar tomography surveys using saline tracer injections have been developed and tested at the U.S. Geological Survey Mirror Lake fractured-rock field-research site in Grafton County, New Hampshire to delineate transmissive fracture zones and image fluid flow at a scale of a meter to about 100 meters (m). High concentration (20-50 gram per liter) sodium chloride tracers injected into transmissive fractures increase the electromagnetic (EM) attenuation observed in cross-hole radar scans as compared to the observed background attenuation. The observed differences in EM attenuation are inverted to produce attenuation-difference tomograms.

Attenuation-difference tomograms acquired under 'steady-state' injection and pumping conditions were used to delineate the locations and orientations of transmissive fracture zones between boreholes. Time-lapse radar-tomography methods can monitor slug-injection saline tracer tests and image fluid flow paths in fractured-rock. Time-lapse cross-hole radar data sets were acquired at Mirror Lake by using controlled injections of fixed volumes of a high-concentration saline tracer, while scanning small sections of the tomographic image. Equivalent time data from each scanned section are sorted, analyzed to determine attenuation differences, and inverted. Time-lapse attenuation-difference tomograms delineate transmissive zones, identify variability within transmissive zones, and provide kinematic information that images ground-water flow and transport at a scale of a meter to 100 m.

The location of transmissive zones within the tomographic image plane and tracer travel times to the image plane are provided by steady-state and time-lapse attenuation-difference tomograms. Results of steady-state and time-lapse tomography surveys were used to help construct and calibrate ground-water flow and transport models in the FSE well field.

Time-lapse tomography would be more useful if time-dependent attenuation changes could be used to estimate tracer specific conductance and concentration at the image plane. A simple effective medium method of analyzing time-dependent attenuation changes to estimate tracer specific conductance was tested on radar data acquired over a meter-scale fractured granite block. Preliminary results illustrate the importance of estimating secondary porosity accurately, and suggest that robust analysis may require (1) accounting for effects of EM scattering on attenuation, and (2) modifying field methods to include several steady-state injection tests using different tracer concentrations.

Introduction

In fractured-rock aquifers, direct observation of fractures and measurement of hydraulic properties is limited by the location, number, and orientation of boreholes. Geophysical methods can supplement direct observations by measuring physical-property changes induced by fractures at borehole to field scales. Cross-hole radar tomography is one of the geophysical methods that has been used at the U.S. Geological Survey (USGS) Mirror Lake fractured-rock field-research site in the Hubbard Brook Experimental Forest, Grafton County, New Hampshire (fig. 1), to image fracture zones and lithologic changes at field scales useful for flow and transport modeling.

The interpretation of radar anomalies to identify transmissive fractures has been improved at Mirror Lake by combining borehole-radar surveys in cross-hole tomography and single-hole reflection modes with the injection of high-salinity sodium chloride (NaCl) (20-50 grams per liter (g/l) NaCl) tracers (Lane and others, 1996; Wright and others, 1996; Day-Lewis and others, 1997; Lane, Haeni, and Versteeg, 1998; Lane, Haeni, and Day-Lewis, 1998; Liu and others, 1998; Wright and Lane, 1998).

Figure 1. Location of study area and the FSE well field at the U.S. Geological Survey Fractured-Rock Field Research site, Mirror Lake, Grafton County, New Hampshire.

Saline tracers are electrically conductive. The attenuation of an electromagnetic (EM) wave that propagates across a fracture increases if the electrical conductivity of the water within that fracture is increased. By conducting cross-hole radar surveys before, during, and after saline tracer tests, it is possible to identify differences in EM attenuation induced by transport of the tracer through transmissive fractures. Differences in attenuation can be analyzed tomographically to image transmissive zones between boreholes (Ramirez and Lytle, 1986; Niva and others, 1988; Olsson and others, 1992).

This paper summarizes methods developed at Mirror Lake that combine cross-hole radar tomography with saline tracer injections to delineate transmissive fractures and image fluid flow.

Field Experiments

A series of field experiments was begun in 1995 to test and develop cross-hole radar attenuation-difference tomography methods in fractured rock. The experiments were conducted at the USGS Mirror Lake fractured-rock field-research site in the Hubbard Brook Experimental Forest, Grafton County, New Hampshire. A description of the hydrogeology of the Mirror Lake site is given in Shapiro and Hsieh (1991, 1996) and Shapiro and others (1995). Additional experimental details and results are given in Lane and others (1996), Lane, Haeni, and Day-Lewis (1998), Lane, Haeni, and Versteeg (1998), and Wright and Lane (1998).

Cross-hole radar tomography surveys were conducted with instruments designed and built by the USGS and with commercially available systems, using borehole antennas with center frequencies ranging from 30 to 100 megahertz (MHz). The experiments have been conducted at the FSE 1-4 cluster within the FSE well field, an arrangement of four boreholes that approximate a 9-meter (m) square (fig. 2).

Figure 2. Plan view of FSE 1 to 4 borehole cluster, FSE well field, Mirror Lake, Grafton County, New Hampshire.

The experiments focused on tomographic imaging of a transmissive zone connecting the boreholes at a depth of about 40 m. Straddle-packers were used to isolate the transmissive zone in the injection and pumped boreholes (FSE-1 and FSE-4; fig. 3). NaCl solutions in concentrations ranging from 20-50 g/L were used as tracers. Different tracer injection procedures and pumping rates were used, depending on the objectives of the experiment. In 1995 and 1996, the transmissive zone in the observation boreholes (FSE-2 and FSE-3; fig. 2) was left open to permit radar logging. In 1997, specially constructed, reusable PVC packers were used. These packers allow radar and other borehole logs to be collected through the PVC core pipe that suspends the packers (fig. 4). The PVC packers were used to isolate the transmissive zone in the injection and observation boreholes (FSE 1-3) to minimize movement of tracer into the radar-logging boreholes.

Figure 3. Arrangement of PVC and conventional straddle packers used to isolate a transmissive zone in FSE-1 and FSE-4.

Robust tomographic inversion of attenuation-difference data requires that any change in the distribution and concentration of the tracer that occurs during radar-data acquisition be small. One way this 'steady-state' requirement has been satisfied at Mirror Lake is through near-continuous injection and pumping of the tracer during radar-data acquisition.

'Steady-state' attenuation-difference tomograms delineate transmissive zones within the tomographic image plane. For example, figure 5 shows an attenuation difference tomogram between FSE-2 and FSE-3. The attenuation difference anomalies in figure 5 are consistent with a sub-horizontal fracture zone and a steeply dipping fracture zone. This interpretation is qualitatively consistent with the pattern of fractures observed intersecting FSE-2 and FSE-3 on acoustic televiewer logs (F.L. Paillet, U.S. Geological Survey, written commun., 1994), borehole video logs (Johnson and Dustan, 1998), and results of single-hole directional radar surveys in the FSE 1-4 cluster (Lane and others, 1996). Steady-state attenuation tomograms provide insights about the location and geometry of transmissive zones in fractured rocks, but do not provide time-dependent information useful for understanding flow and transport.

Cross-hole radar methods can record transient hydraulic processes. For example, in Wright and Lane (1998), repeated cross-hole radar scanning during the start of an injection test identified the 'break-through' of the tracer as it passed across the image plane (fig. 6). The use of conventional cross-hole radar tomography methods to image time-dependent processes is difficult at Mirror Lake and other fractured-rock sites because significant changes in tracer location and concentration can occur in minutes, whereas a complete cross-hole radar tomography survey can require hours.

Figure 4. Photograph of log-through PVC packer assembly developed at Mirror Lake.

In order to monitor field-scale slug-injection saline-tracer tests, a time-lapse attenuation-difference tomography method was developed using sequential tracer injection and incremental cross-hole radar scanning (Day-Lewis and others, 1997; Lane, Haeni, and Day-Lewis, 1998). The method requires carefully repeating a dipole saline-tracer injection test using a small fixed volume of saline tracer.  During tracer injection and recovery, a portion of the tomographic image plane is repeatedly scanned (fig. 7).  The start of each scan is timed relative to the start of the injection cycle to permit equivalent time sorting of the data.  The amount of time required to complete one scan is minimized to meet the 'steady-state' assumption, while maximizing temporal resolution.  The cross-hole data from each section collected during equivalent time intervals are merged to form a time-lapse series of tomography data sets suitable for attenuation-difference analysis and for tomographic inversion.

Figure 5. 30 MHz attenuation-difference tomogram between FSE-2 and FSE-3 in the FSE well field at Mirror Lake, New Hampshire. Interpreted reflectors from single-hole directional borehole radar surveys in the FSE 1-4 cluster are superimposed on the tomogram. Dark lines represent known transmissive zones.

Figure 6. Common-depth cross-hole radar amplitudes plotted against measurement depth between FSE-2 and FSE-3 in the FSE well field at Mirror Lake N.H. for six logging runs conducted over a 2-hour time period starting at the onset of tracer injection. Amplitude decreases between 42 and 46 meters record the arrival and breakthrough of tracer across the image plane (after Wright and Lane, 1998).

Figure 8 shows the effects of tracer on EM wave attenuation. Wave attenuation behavior with time resembles 'break-through' curves. These waves record the passage of the tracer across the image plane. The attenuation of waves traversing non-transmissive regions remains unchanged with time.

Tomographic inversion of equivalent time data produces a series of attenuation-difference 'snapshots' that delineate the location and orientation of attenuation-difference anomalies and identify kinematic changes in attenuation associated with the transport of the saline tracer. For example, figure 9 contains a subset of 31 tomograms produced from time-lapse cross-hole radar monitoring of a slug-injection saline tracer test conducted at the FSE well field in 1997. The tomograms show the general location, geometry, and kinematic characteristics of attenuation anomalies in the FSE-2 to FSE-3 plane.

Figure 7. Radar-data acquisition method used for time-lapse radar monitoring of a slug-injection saline tracer test conducted at the FSE well field, Mirror Lake, New Hampshire, in 1997. Transmitter (Tx) - receiver (Rx) geometry used for consecutive saline-tracer injections; (a) fixed and moving antenna locations for day 1, (b) complete transmitter-receiver pattern for each day.

The time-lapse tomography results are consistent with hydraulic tests (Hsieh and Shapiro, 1996), 'steady-state' attenuation-difference tomograms (Lane and others, 1996; Wright and Lane, 1998), and results of single-hole directional radar surveys in the FSE 1-4 cluster (Lane and others, 1996) (fig. 10). In addition, the time-lapse tomography results indicate that within the transmissive zone connecting FSE 1-4, a high- permeability pathway exists, connecting FSE-1 to FSE-4 through fractures that pass through or near FSE-2.

Figure 8. Examples of time-varying effects of saline tracer on wave attenuation history.

Time-lapse radar attenuation-difference tomography results can be used in flow and transport modeling. For example, the location and orientation of attenuation-difference anomalies and travel times interpreted from tracer 'break-through' across the image plane along with results of previous USGS work in the FSE well field (Hsieh and Shapiro, 1996) were used by Day-Lewis (Day-Lewis and others,1997; Lane, Haeni, and Day-Lewis, 1998) and Shapiro (Shapiro and others, 1998) to help construct and calibrate simplified ground-water flow and transport models of the FSE 1-4 cluster using MODFLOW (McDonald and Harbaugh, 1988) and MT3D (Zheng, 1990).

Analysis of Attenuation Differences to Estimate Image-Plane Tracer Concentration

Time-lapse cross-hole radar tomography methods would be more useful for flow and transport modeling in fractured rock if observed time-dependent radar attenuation differences could be interpreted to estimate tracer concentrations. The relationship between time-dependent attenuation differences and outlet concentration is shown in figure 11. Outlet chloride concentration and integrated tomogram attenuation changes (sum of pixel attenuation) from the 1997 experiment are shown plotted against time. The shapes of the integrated attenuation-difference and chloride concentration curves are remarkably similar, including double-peaks at 100 and 200 minutes.

Figure 9. 100 MHz Time-lapse attenuation-difference tomograms between FSE-2 and FSE-3 at the FSE well field, Mirror Lake N.H., produced using a sequential injection and incremental scanning method.

Figure 10. 100 MHz attenuation-difference tomogram between FSE-2 and FSE-3 extracted from a time-lapse radar survey. Selected single-borehole directional-radar reflectors from the FSE 1 to 4 cluster are projected onto the FSE-2 to FSE-3 tomography plane.

Figure 11. Chloride concentration in milligrams per liter and integrated radar attenuation-difference normalized to maximum and minimum values plotted against time.

In Lane, Joesten, and others (1998), a simple effective medium approach was used to interpret attenuation differences observed during a saline tracer injection experiment in carbonate rocks to estimate changes in total dissolved solids. Effective medium analysis uses 'mixing' laws and known or measured physical properties of individual constituents to interpret a measured physical property (such as EM attenuation).

It is unclear if the same effective medium approach can be applied to radar attenuation-difference data from saline tracer tests in fractured rock. Effective medium analysis is based on the assumption that the medium is homogeneous on the measurement scale. This assumption may be invalid in fractured rocks because fractures can have random or arbitrary distribution, spatial density, orientation, and scale-length. Another complication is reflection and scattering of EM waves by fractures. EM attenuation in fractured rock is a measure of scattering losses as well as conductive losses. The effective medium approach used by Lane, Joesten, and others (1998) does not explicitly account for the effects of EM scatter. Another problem with the effective medium approach in fractured rocks is the linkage between EM attenuation, porosity, and fluid specific conductance. Equivalent EM-attenuation changes can be expected from different combinations of porosity and specific conductance.

Despite these problems, the effective medium approach may have merit where secondary porosity can be estimated. For example, the effective medium approach was applied to radar transmission data obtained over a meter-scale block of fractured granite. The sub-horizontal fracture penetrating the block has an aperture of about 2 millimeters, which corresponds to an average secondary porosity of about 1.5 x 10^-3. The edges of the fracture are sealed to prevent leakage; plastic valves installed in the edges of the block permit the injection and withdrawal of fluids. The radar transmission data shown in figure 12 were acquired through the center of the block by using broadband electric-dipole impulse-antennas with a center frequency of about 870 MHz. Saturating the fracture and increasing the NaCl concentration of the water in the fracture decreases the transmitted pulse amplitude (fig. 13). EM-attenuation change is given by:

(1)

where:

Da is the EM attenuation change,
A_b is the background transmitted pulse amplitude, and
A_s is the transmitted pulse amplitude for specific conductance, s.

Figure 12. 870 MHz cross-block radar-pulse waveforms recorded after passing through the center of a meter-scale fractured granite block. Data shown are for an unsaturated fracture (largest amplitude), fracture saturated with tap-water (specific conductance about 150 microsiemens per centimeter ) and fracture saturated with a 64 g/L NaCl solution (smallest amplitude).

The dotted line in figure 13 shows observed EM attenuation changes calculated from the physical model data plotted against fluid specific conductance. As specific conductance increases, EM attenuation increases. The effective media method used here is based on the assumption that attenuation changes are related to the fluid specific conductance (s fluid) and secondary porosity (f fracture):

(2)

Predicted attenuation changes for several values of secondary porosity plotted against tracer specific conductance using the EM analysis method given in Lane, Joesten, and others (1998) are also shown in figure 13. Note the effect of secondary porosity on the magnitude and rate of change of attenuation with respect to specific conductance. The attenuation-difference data from the physical model correspond with predicted values assuming a secondary porosity of 1.8x10^-3. The secondary porosity at the center of the granite block inferred by effective media analysis is significantly different from the estimated average value of 1.5x10^-3. The results could indicate: (1) secondary porosity (i.e. fracture aperture) is larger over the measured interval than the mean value for the block and/or (2) scattering losses and/or other loss factors are significantly increasing attenuation.

Figure 13. Predicted attenuation-difference plotted against specific conductance for selected values of secondary porosity and measured attenuation-differences from the center of a meter-scale fractured granite block for a range of tracer specific conductance (black squares). Measured attenuation differences plot along the 0.0018 secondary porosity line. Estimated block secondary porosity is 0.0015.

These results suggest the analysis of attenuation-difference data from saline tracer tests using an effective media approach could have merit if accurate estimates of secondary porosity can be made, but might require modification to account for scattering losses or other loss mechanisms. One possible approach is suggested by the effect of secondary porosity on attenuation-difference shown in figure 13. Secondary porosity is inversely proportional to the rate of change of attenuation with specific conductance. Conducting several 'steady-state' experiments using different tracer concentrations could provide data to estimate secondary porosity within the tomographic image plane. These estimates could then be used to interpret time-lapse attenuation differences from slug-injection saline tracer tests in terms of specific conductance or tracer concentration.

Conclusion

Methods of coupling cross-hole radar tomography surveys using saline tracer injections have been developed and tested at the USGS Mirror Lake fractured-rock field-research site in Grafton County, New Hampshire to delineate transmissive fracture zones and image fluid flow at field-scales. High concentration (20-50 g/L) NaCl tracers injected into transmissive fractures increase EM attenuation observed in cross-hole radar scans compared to background measurements. Changes in EM attenuation are inverted to produce attenuation-difference tomograms.

Attenuation-difference tomograms acquired under 'steady-state' injection and pumping conditions were used to delineate the location and orientation of transmissive fracture zones between boreholes. Time-lapse radar tomography methods can monitor slug-injection saline tracer tests and image fluid flow in fractured rock. Time-lapse cross-hole radar sets acquired at Mirror Lake have coupled the controlled injection of fixed volumes of high-concentration saline tracer with the scanning of small sections of the tomographic image. Equivalent time data from each scanned section are sorted, analyzed to determine attenuation-differences, and inverted. Time-lapse attenuation-difference tomograms delineate transmissive zones, identify variability within transmissive zones, and provide kinematic information that images field-scale ground water flow and transport.

The locations of transmissive zones within the tomographic image plane are shown by steady-state attenuation difference tomograms. Travel times across the image plane are provided by time-lapse attenuation-difference tomograms. Results of steady-state and time-lapse tomography surveys were used to help construct and calibrate ground water flow and transport models in the FSE well field.

Time-lapse tomography would be more useful if time-dependent attenuation changes could be used to estimate tracer specific conductance and concentration at the image plane. A simple effective media method of analyzing time-dependent attenuation changes to estimate tracer specific conductance was tested on radar data acquired over a meter-scale fractured granite block. Preliminary results illustrate the importance of accurately estimating secondary porosity, and suggest robust analysis may require (1) accounting for effects of EM scattering on attenuation, and (2) modifying field methods to include several steady-state injection tests using different tracer concentrations.

Acknowledgments

The Hubbard Brook Experimental Forest is operated and maintained by the Northeastern Forest Experiment Station, USDA Forest Service, Radnor, Pennsylvania.

References

Day-Lewis, F.D., Lane, J.W. Jr., Haeni, F.P., and Gorelick, S.M., 1997, One approach to identifying flow paths in fractured rock--combining borehole radar, saline tracer tests, and numerical modeling [abs.]: EOS, Transactions, American Geophysical Union, v. 78, no. 46, p. F322.

Hsieh, P.A., and Shapiro, A.M., 1996, Hydraulic characteristics of fractured bedrock underlying the FSE well field at the Mirror Lake site, Grafton County, New Hampshire, in Morganwalp, D.W., and Aronson, D.A., eds., U.S. Geological Survey Toxic Substances Hydrology Program-Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993: U.S. Geological Survey Water-Resources Investigation Report 94-4015, p.127-130.

Johnson, C.D., and Dunstan, A.M., 1998, Lithology and fracture characterization from drilling investigations in the Mirror Lake area--from 1979 through 1995 in Grafton County, New Hampshire: U.S. Geological Survey Water-Resources Investigations Report 98-4183, 210 p.

Lane, J.W., Jr., Haeni, F.P., and Day-Lewis, F.D., 1998, Use of time-lapse attenuation difference radar tomography methods to monitor saline tracer transport in fractured crystalline bedrock, in Seventh International Conference of Ground Penetrating Radar (GPR'98), Lawrence, Kansas, May 27-30, 1998., Proceedings: Lawrence, Kans., University of Kansas, Radar Systems and Remote Sensing Laboratory, p. 533-538.

Lane, J.W., Jr., Haeni, F.P., Placzek, Gary, and Wright, D.L., 1996, Use of borehole radar methods to detect a saline tracer in fractured crystalline bedrock at Mirror Lake, Grafton County, New Hampshire, in Sixth International conference of Ground Penetrating Radar (GPR'96), Sendai, Japan, September 30-October 3, 1996, Proceedings: Sendai, Japan, Tohoku University, Department of Geoscience and Technology, p. 185-190.

Lane, J.W., Jr., Haeni, F.P., and Versteeg, Roelof, 1998, Use of a multi-offset borehole-radar reflection method in fractured crystalline bedrock at Mirror Lake, Grafton County, New Hampshire, in Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP), Chicago, Illinois, March 22-26, 1998, Proceedings: Wheat Ridge, Colo., Environmental and Engineering Geophysical Society, p. 359-368.

Lane, J.W., Jr., Joesten, P.K., Haeni, F.P., Vendl, Mark, and Yeskis, Doug, 1998, Use of borehole radar methods to monitor the movement of a saline tracer in carbonate rock at Belvidere, Illinois, in Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP), Chicago, Illinois, March 22-26, 1998, Proceedings: Wheat Ridge, Colo., Environmental and Engineering Geophysical Society, p. 323-332.

Liu, Lanbo, Lane, J.W., Jr., and Quan, Youli, 1998, Radar attenuation tomography using the frequency downshift method: Journal of Applied Geophysics, v. 40, p. 105-116.

McDonald, M.G., and Harbaugh, A.W., 1988, Modular three-dimensional finite-difference ground-water flow model: U.S. Geological Survey Techniques of Water-Resources Investigations, book 6, chap. A1, 586 p.

Niva, B., Olsson, O., and Blumping, P., 1988, Radar cross-hole tomography at the Grimsel Rock Laboratory with application to migration of saline tracer through fracture zones: Nationale Genossenschaft fur die lagerung radioaktiver Abfalle, NTB 88-31.

Olsson, O., Andersson, P., Carlsten, S., Falk, L., Niva, B., and Sandberg, E., 1992, Fracture characterization in crystalline rocks by borehole radar, in Pilon, J., ed., Ground Penetrating Radar: Geological Survey of Canada Paper 90-4, p. 139-150.

Ramirez, A.L., and Lytle, R.J., 1986, Investigation of fracture flow paths using alterant geophysical tomography: Journal of Rock Mechanics and Mining Sciences and Geomechanics, v. 23, no. 2, p.165-169.

Shapiro, A.M., and Hsieh, P.A., 1991, Research in fractured-rock hydrogeology--characterizing fluid movement and chemical transport in fractured rock at the Mirror Lake drainage basin, New Hampshire, in Mallard, G.E., and Aronson, D.A., eds., U.S. Geological Survey Toxic Substances Hydrology Program-Proceeedings of the Technical Meeting, Monterey, California, March 11-15, 1991: U.S. Geological Survey Water-Resources Report 91-4034, p. 155-161.

Shapiro, A.M., and Hsieh, P.A., 1996, Overview of research on use of hydrologic, geophysical, and chemical methods to characterize flow and chemical transport in fractured rock at the Mirror Lake site, New Hampshire, in Morganwalp, D.W., and Aronson, D.A., eds., U.S. Geological Survey Toxic Substances Hydrology Program-Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993: U.S. Geological Survey Water Resources Investigations Report 94-4015, p. 71-80.

Shapiro, A.M., Hsieh, P.A., and Winter, T.C., 1995, The Mirror Lake fractured rock research site-a multidisciplinary research effort in characterizing ground-water flow and chemical transport in fractured rock: U.S. Geological Survey Fact Sheet FS-138-95, 2 p.

Shapiro, A.M., Lane, J.W., Jr., and Day-Lewis, F.D., 1998, Characterizing heterogeneity in fractured rock through a combination of tracer testing and radar tomography: EOS, Transactions of the American Geophysical Union, v. 79, no. 17, p. S134.

Wright, D.L., Grover, T.P., Ellefsen, K.J., Lane, J.W., Jr., and Kase, P.G., 1996, Radar tomograms at Mirror Lake, New Hampshire--3-D visualization and a brine tracer experiment in Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP), Keystone, Colorado, April 28-May 2, 1996, Proceedings: Wheat Ridge, Colorado, Environmental and Engineering Geophysical Society, p. 565-575.

Wright, D.L., and Lane, J.W., Jr., 1998, Mapping hydraulically permeable fractures using directional borehole radar and hole-to-hole tomography with a saline tracer, in Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP), Chicago, Illinois, March 22-26, 1998, Proceedings: Wheat Ridge, Colo., Environmental and Engineering Geophysical Society, p. 565-575.

Zheng, C., 1990, MT3D--A modular three-dimensional transport model for simulation of advection, dispersion and chemical reactions of contaminants in ground-water systems: S.S. Papadopulos & Associates, Inc.

Author Information

John W. Lane, Jr., U.S. Geological Survey, Storrs Mansfield, Connecticut (jwlane@usgs.gov)

David L. Wright, U.S. Geological Survey, Denver, Colorado (dwright@usgs.gov)

F. Peter Haeni, U.S. Geological Survey, Storrs Mansfield, Connecticut

*

Final copy as submitted to USGS Toxic Substances Hydrology Program for publication as: Lane, John W., Jr., Wright, David L., and Haeni, F. Peter, 1999, Borehole Radar Tomography using Saline Tracer Injections to Image Fluid Flow in Fractured Rock, in Morganwalp, D.W. and Buxton, H.T., eds., U.S. Geological Toxic Substances Hydrology Program -- Proceedings of the Technical Meeting, Charleston, South Carolina, March 8-12, 1999, USGS Water-Resources Investigations Report 99-4018C, v. 3, p. 747-756.