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The Influence Of Pore Fluid Chemistry On The Induced Polarization Response Of Rocks And Soils
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 11th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, Mar 1998, cp-203-00080
Abstract
To improve contaminant detection and monitoring, it is important to understand the role<br>of the bulk pore fluid chemistry on the induced polarization (IP) response of rocks and soils. IP<br>methods can be more effective than traditional resistivity surveys because they are more<br>sensitive to changes in electrochemistry at the mineral grain-pore fluid interface caused by small<br>amounts of dissolved contaminant. Clean and contaminated materials have been shown to have<br>comparatively different IP responses in both laboratory and field experiments. However,<br>electrochemical surface properties are also dependent on the bulk pore fluid chemistry and grain<br>microgeometry. The effect of contaminants on the IP response is superimposed upon these other<br>bulk fluid and microgeometry effects.<br>To document the influence of pore fluid chemistry on the IP response of earth materials,<br>experiments were performed to measure the complex conductivity and time domain IP of Berea<br>sandstone cores as a function of pore fluid pH, ionic strength, and cation type. A minimum in<br>surface conductivity and IP response is observed at pH 3, the approximate point of zero net<br>surface charge for quartz. While surface conductivity increases with ionic strength, the net IP<br>response, or phase angle, decreases with ionic strength. A suite of cores saturated with different<br>salt solutions of equal conductivity demonstrates significant variability in the IP response as a<br>function of cation type. These experiments are applicable to other quartz-dominated systems and<br>help to link field IP measurements to geochemical parameters, thus improving the IP<br>characterization of geochemical environments.