Assurance monitoring for long term insight of hydrological processes.
The use of electrically-based geophysical techniques, such as resistivity or induced polarization, to monitor the subsurface have been pioneered and performed by HGI for well over a decade. While electrical resistivity methodologies are typically employed to image the subsurface at a single point in time, HGI has developed new ways to apply resistivity for time lapse monitoring of hydrodynamic processes. Termed ‘Assurance Monitoring’ the methodology involves using geophysics to monitor changes in soil saturation over time in order to solve problems related to potential system failure (example: slope failures due to fluid loading). The repeated resistivity measurements show subsurface soil saturation changes, thus giving significant information relating to changing conditions and impacts that those changes may have. In short, we help to reduce risk of containment facilities.
HGI has pioneered the application of Assurance Monitoring using electrically-based geophysical methods in order to better understand hydrodynamic processes and reduce risk of containment facilities.
For example, the long-term geotechnical stability of a heap relies on a balance of restoring and disturbing forces, and are heavily dependent on pore pressure loadings within heaps. Pore pressures are affected by the permeability and drainage characteristics of fluid as it moves through the subsurface. Assurance monitoring with resistivity allows you to track changes in these flow regimes over a broad time scale at any frequency. These measurements have ability to provide large-scale monitoring to obtain electrical properties that are directly related to the movement of electrolytic solutions. Depending on the reasons for assurance monitoring, this process can be conducted periodically or continually, over vast areas in a short amount of time. Additionally, because the physical application of this technology is non-invasive it can provide high value information at very low cost when compared to drilling, CPT, and well sampling. Each snapshot comprises a profile contoured section that can be compared to previously captured snapshots which track changes in resistivity likely caused by increasing and decreasing saturation of the material being monitored.
Other potential applications include monitoring solution infiltration through earth media, leachate formation within a landfill, grout injected into a void, dam stability, heap slope stability, and monitoring potential contaminant emissions from large underground waste tanks.