This project demonstrated the use of geophysical techniques to provide near real-time, noninvasive, and cost-effective information on the spatial and temporal distribution of amendments. The technology used electrical resistivity measurements from a series of wells to detect changes in electrical conductivity. Electrical resistivity monitoring is particularly useful for enhanced bioremediation because the amendment solutions used for bioremediation increase the electrical conductivity of the subsurface significantly above the background conductivity. Time-lapse electrical resistivity monitoring can delineate where amendments were initially delivered, as well as track their migration and depletion over time. Near real-time information is particularly valuable because it can allow modifications and/or additional injections while equipment is still present on site.
A follow-on effort, Demonstrating a Biogeophysics Strategy for Minimally Invasive Post Remediation Performance Assessment (ER-201579), is aimed at demonstrating the utility of electrical resistivity imaging for monitoring the long-term impacts of bioremediation.
The system demonstrated is referred to as the Hydrogeophysical Performance Monitoring System (HPMS). The HPMS consisted of commercially available hardware and custom designed software for data collection, data transfer, data processing, and web-based result visualization. Two demonstrations of the HPMS were performed at the Brandywine Defense Reutilization and Marketing Office (DRMO) site in Brandywine, Maryland. The first demonstration, which lasted from March 2008 until the summer of 2010, involved injection of a proprietary lactate amendment (Anaerobic BioChem [ABC®]). The second demonstration, in August 2010, involved monitoring two injections of molasses, and showcased the delivery of near real-time results to project team members and program managers in the field.
Both the 2008 and the 2010 field campaigns successfully demonstrated the ability of electrical geophysical monitoring to provide near real-time, actionable information on the spatial and temporal behavior of amendments for considerably less cost than invasive sampling (see time lapse imaging results in the Objective section). The estimated cost of the HPMS system was roughly half the cost of invasive sampling, while providing more complete and timely information on the amendment distribution. During the 2008 demonstration, the time-lapse electrical resistivity images revealed not only the distribution and transport of injected bio-amendment over time, but also the effects of biogeochemical alterations induced by the amendment. Changes in subsurface electrical properties associated with amendment-induced microbial activity were noted long after the amendment had been removed from the system through groundwater transport, thereby demonstrating the opportunity to monitor the long-term impacts of enhanced bioremediation using time-lapse electrical geophysical imaging methods that prompted the current project. The shorter, real-time imaging demonstration in 2010 proved the system can provide stakeholders with actionable information on amendment transport behavior within 30 minutes after injection.
Current technologies for assessing the success of emplacement primarily rely on direct measurements in wells. Such measurements are expensive and time-consuming, and they provide only limited spatial and temporal information. The HPMS provides two main benefits: first, far fewer wells will be required for understanding amendment distributions, particularly when surface electrodes are deployed, leading to significant cost savings (20 to 50% or greater per site), and second, rapid identification of missed target zones will enable optimal amendment application and thus increase efficiency. Overall, the system will provide low-cost, near-real-time, volumetric information that will reduce overall monitoring cost and increase monitoring performance.
K. Singha, F. D. Day-Lewis, T. Johnson, and L. D. Slater. 2015. Advances in Interpretation of Subsurface Processes with Time-Lapse Electrical Imaging. Hydrological Processes, Hydrological Processes, 29(6):1549–1576.
Johnson, T.C., R.J. Versteeg, F.D. Day-Lewis, W. Major, and J.W. Lane Jr. 2014.Time-Lapse Electrical Geophysical Monitoring of Amendment-Based Biostimulation. Groundwater, 53(6): 920-932.
Johnson, T.C., R.J. Versteeg, A. Ward, F.D. Day-Lewis, and A. Revil. 2010. Improved Hydrogeophysical Characterization and Monitoring through Parallel Modeling and Inversion of Time-Domain Resistivity and Induced-Polarization Data. Geophysics, 75( 4): WA27–WA41.
Versteeg, R.J. and T.C. Johnson. 2008. Using Time-Lapse Electrical Geophysics to Monitor Subsurface Processes. The Leading Edge, 27(11):1488-1497.
Revil, A., M. Karaoulis, T.C. Johnson & A. Kemna. 2007. Review: Some Low-Frequency Electrical Methods for Subsurface Characterization and Monitoring in Hydrogeology. Hydrogeology Journal, 15(6):617-658.