THE RELATIONSHIP BETWEEN ELECTRICAL RESISTIVITY AND BIOGENIC FREE PHASE GAS (FPG) BUILD UP IN PEAT SOILS

A study was conducted to evaluate the contribution of electrical resistivity (ER) and induced polarization (IP) measurements for quantifying the spatial and temporal evolution of biogenic free phase gas (FPG) in peat soils at multiple depths and at varying scale from the point scale (support volume for four closely spaced electrodes) and the scale of an electrical tomography survey performed on a network of electrodes. We performed laboratory measurements to delineate (1) vertical profiles of ER on five resistivity arrays (2) tomographic imaging of ER (3) peat deformation at multiple depths using multiple rods and (4) combustible gas concentration. Changes in resistivity (± 10%) were observed and believed to reflect the build up and subsequent release of methane. Resistivity depth profiles clearly reveal that resistivity decreases near the peat surface, increases in the middle, yet decreases gradually at the bottom of the peat block. The decrease in resistivity at the top portion may be related to the peat expansion and porosity increase associated with biogenic gas generation whereas at the base it may be related to the increased ionic concentration of the pore water as a by product of methanogenesis. Further studies are aimed at detecting the changes of ionic concentration and pH of pore fluids at different depths of the peat soil.