Investigating the effective resistivity of reinforced concrete waste storage tanks at the Hanford Site

Abstract

Industrialized sites pose challenges for conducting electrical resistivity geophysical surveys because the sites typically contain metallic infrastructure that can mask electrolytic-based soil and groundwater contamination. The Hanford Nuclear Site in eastern Washington State, USA, is an industrialized site with underground storage tanks, piping networks, steel fencing, and other potentially interfering infrastructure that could inhibit the effectiveness of electrical resistivity tomography (ERT) to map historical and monitor current waste releases. The underground storage tanks are the largest contributor by volume to subsurface infrastructure and can be classified as reinforced concrete structures with an internal steel liner. Directly measuring the effective value for the electrical resistivity of the tanks, that is, the combination of individual components that comprise the tank’s shell, is not reasonably possible because they are buried and are dangerously radioactive. Therefore, we indirectly assess the general resistivity of the tanks and the surrounding infrastructure by developing synthetic ERT models with a parametric forward-modeling study using a wide range of resistivity values from [Formula: see text] to [Formula: see text], which are equivalent to steel and dry rock, respectively. The synthetic models use the long-electrode ERT (LE-ERT) method, whereby steel-cased metallic wells surrounding the tanks are used as electrodes. The patterns and values of the synthetic tomographic models are then compared with LE-ERT field data from the AX tank farm at the Hanford Site. This indirect method of assessing the effective resistivity reveals that the reinforced concrete tanks are electrically resistive and the accompanying piping infrastructure has little influence on the overall resistivity distribution when using electrically based geophysical methods for characterizing or monitoring waste releases. Our findings are consistent with nondestructive testing literature that also indicates reinforced concrete to be generally resistive.