USGS Groundwater Information: Branch of Geophysics
Figure 1. Peter Joesten (USGS OGW BG) processes preliminary borehole radar data at the former Loring Air Force Base, Maine. White casing on the left is for antenna storage.
In 2002 the USGS Office of Ground Water, Branch of Geophysics (OGW BG) used single-hole radar reflection and crosshole radar tomography surveys in conjunction with conventional borehole-geophysical methods to evaluate the effectiveness of borehole-radar methods for monitoring the movement of steam and heat through fractured bedrock.
OGW BG, in cooperation with U.S. Environmental Protection Agency (USEPA), conducted geophysical surveys in an abandoned limestone quarry at the former Loring Air Force Base. The surveys were conducted during a field-scale, steam-enhanced remediation (SER) pilot project in 2002 to study the viability of SER to remediate non-aqueous phase liquid (NAPL) contamination in fractured bedrock.
The SER pilot study was conducted by the USEPA, the U.S. Air Force (USAF), and the Maine Department of Environmental Protection. The purpose of the steam injection was to flush contaminated groundwater into extraction wells and to vaporize volatiles that could then be removed through a vapor extraction system.
Accurate monitoring of remediation efforts is vital to our understanding and evaluation of its effectiveness. Information on where steam has replaced water in bedrock fractures and on related subsurface temperature changes can be used to assess if the steam injection is reaching the intended target areas. These data can be used to inform decisions on remedial activities and set up in order to evaluate and (or) improve the remedial action.
Figure 2. Colette Grégoire (Katholieke Universiteit Leuven, Belgium) lowers radar antenna in borehole at the former Loring Air Force Base, Maine.
OGW BG conducted single-hole radar reflection and hole-to-hole radar tomography in two monitoring wells at the SER site. Temperature and electromagnetic-induction logs were also collected to provide additional information to augment the radar data analysis. Background geophysical logs were collected prior to the start of the steam injection, and additional logs were collected at two different times during the actual injection.
Numerical modeling was used to predict the changes in radar-wave velocity and attenuation that could be expected from heating the fluid in fractures and the limestone matrix, from steam replacing water in the fractures, and from changes in the conductive properties of the fluid in fractures. The effect of heating on the reflectivity from fractures also was modeled. The modeling results provided a basis for theoretically assessing the effectiveness of radar methods to monitor SER operations, and for interpreting the radar field data.
Analysis of the radar reflection logs from a borehole where the temperature increased substantially during the steam injection shows an increase in attenuation and a decrease in reflectivity in the vicinity of the borehole. Results of applying a reflection amplitude analysis method developed for this study indicate that steam did not totally replace the water in most of the fractures. The observed decreases in reflectivity were consistent with an increase in fracture-water temperature, rather than the presence of steam.
These results indicate that borehole radar may be an effective tool for detecting the change in fracture filling from water to steam at sites where the fracture apertures are greater than 1 millimeter. The results also indicate that borehole radar has potential to detect substantial changes in temperature in the rock matrix near a borehole.
Figure 3. The 100-megahertz omni-directional borehole-radar reflection data collected in borehole JBW-7817A during August, September, and November 2002 at the former Loring Air Force Base quarry, Limestone, Maine. For more information, see USGS Scientific Investigations Report 2006-5191.
This research was funded by the USEPA Region 1 and the USEPA Technology Innovation Office, with support from the USAF and the USGS Toxic Substances Hydrology Program and in cooperation with Katholieke Universiteit Leuven, Belgium.
Grégoire, Colette, and Joesten, P.K., 2006, Use of borehole radar tomography to monitor steam injection in fractured limestone: Near Surface Geophysics, v. 4, p. 355-365.
Grégoire, Colette, Joesten, P.K., and Lane, J.W. Jr., 2007, Use of borehole-radar methods to monitor a steam-enhanced remediation pilot study at a quarry at the former Loring Air Force Base, Maine: U.S. Geological Survey Scientific Investigations Report 2006–5191, 35 p.
Grégoire, Colette, Joesten, P.K., and Lane, J.W., Jr., 2006, Use of borehole radar reflection logging to monitor steam-enhanced remediation in fractured limestone - Results of numerical modeling and a field experiment: Journal of Applied Geophysics, v. 60, no. 1, p. 41-54, http://dx.doi.org/10.1016/j.jappgeo.2005.12.006.
Grégoire, Colette, Lane, J.W., Jr., and Joesten, P.K., 2005, Steam injection pilot study in a contaminated fractured limestone (Maine, USA) - Modeling and analysis of borehole radar reflection data: 3rd International Workshop on Advanced Ground Penetrating Radar, Delft, The Netherlands, May 2-4, 2005, Proceedings.
Grégoire, C., Lane, J.W., Jr., and Joesten, P.K., 2004, Application of borehole radar for monitoring steam-enhanced remediation of a contaminated site in fractured limestone, Maine, USA, in Hack, R., Azzam, R., and Charlier, R., eds., Engineering Geology for Infrastructure Planning in Europe – a European Perspective, Lecture Notes in Earth Sciences: Berlin, Germany, Springer-Verlag, p. 385-392.
Grégoire, C., Lane, J.W., Jr., and Joesten, P.K., 2004, The use of borehole radar tomography to monitor a steam injection pilot study in a contaminated fractured limestone, in EAGE (European Association of Geoscientists and Engineers) Near Surface Geophysics meeting, 6-9 September, 2004, Utrecht, The Netherlands, Proceedings: Houton, The Netherlands, European Association of Geoscientists and Engineers, 4 p.
For more information on this project, please contact John W. Lane, Jr. (Chief, USGS OGW Branch of Geophysics) or Peter Joesten (USGS OGW Branch of Geophysics), or call the Branch of Geophysics at (860)487-7402.