Induced polarization as a monitoring tool for in-situ microbial induced carbonate precipitation (MICP) processes

Microbial induced carbonate precipitation (MICP) is a promising soil stabilization method performed by stimulating soil microbes that are naturally occurring and ubiquitous in soil systems. The precipitated carbonate acts as a cementation agent to bind loose soil at grain to grain contacts. MICP has been extensively tested and proven in laboratory environments, as well as in limited field trials; however, long term field applications still remain challenging, partly due to quality control and monitoring issues. Induced polarization (IP), an established geophysical method in mineral exploration, is a prime candidate for MICP monitoring and characterization. This study presents the geophysical results of a 15-day field-scale MICP project. The MICP treatment involved the injection of molasses (carbon source for microbial proliferation) and urea in a Ca2+ rich aquifer. IP monitoring successfully delineated, spatially and temporally, the propagation of MICP in the treatment area, while common resistivity measurements failed to capture any MICP related changes. Reduced hydraulic conductivity in the treatment area versus untreated area, further supports that MICP has changed the physical properties of the subsurface. Furthermore, conventional geochemical monitoring as well as X-ray diffraction analysis confirmed carbonate precipitation in samples from discrete wells in the treatment area.