Monitoring air flow and water movement in the subsurface with cross-borehole resistivity and induced polarization

Abstract

The research included in this thesis consists of the following two geophysical surveys: a cross-borehole resistivity and induced polarization tomography survey to track the flow of water in the unsaturated zone at Avra Valley, Arizona; and a cross-borehole resistivity tomography survey to monitor air flow resulting from air sparging in the saturated zone in Florence, Oregon. In Avra Valley, the resistivity decreases from background values in the areas saturated by the injected water, while the IP in these saturated areas increases, indicating that salts may have been flushed out by the descending water. In Florence, Oregon, resistivity increases from background values, delineating the cone-shaped region beginning at the injection point and extending up to the water table where air has displaced water in the saturated zone during sparging, and delineating entrapped air below the water table long after sparging has ceased.