Soil Moisture Monitoring and Sampling Probe for Underground Storage Tanks and Surface Impoundments

Chemical contamination of groundwater has become increasingly prevalent in the U.S. Once thought to be safe from pollution, the underground aquifers that supply drinking water to about half of the U.S. population are now known to be vulnerable to contamination from leaking landfills, waste lagoons, underground storage tanks, improper use of agricultural chemicals, and various industrial operations. Manufactured chemical compounds, including industrial degreasers and solvents, as well as gasoline, pesticides and fertilizers (in all, over 700 synthetic organic chemicals) have seeped down through the soil to the aquifers and been detected in ground water. Nearly every state has identified cases of contamination serious enough to require closing of some public or private supply wells.

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Investigating the Effective Resistivity of Reinforced Concrete Waste Storage Tanks at the Hanford Site

Geophysics ◽

10.1190/geo2021-0187.1 ◽

2021 ◽

pp. 1-50

Author(s):

Allan Haas ◽

Dale F. Rucker ◽

Marc T. Levitt

Keyword(s):

Electrical Resistivity ◽

Reinforced Concrete ◽

Geophysical Methods ◽

Underground Storage ◽

Storage Tanks ◽

Hanford Site ◽

Underground Storage Tanks ◽

Effective Resistivity ◽

Geophysical Surveys ◽

Wide Range

Industrialized sites pose challenges for conducting electrical resistivity geophysical surveys, as the sites typically contain metallic infrastructure that can mask electrolytic-based soil and groundwater contamination. The Hanford 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 tank, i.e., the combination of individual components that comprise the tanks shell, is not reasonably possible because they are buried and dangerously radioactive. Therefore, we indirectly assess the general resistivity of the tanks and surrounding infrastructure by developing synthetic ERT models with a parametric forward modeling study using a wide range of resistivity values from 1×10−6 to 1×104 ohm-m, which are equivalent to steel and dry rock, respectively. The synthetic models used the long-electrode ERT method (LE-ERT), whereby steel cased metallic wells surrounding the tanks are used as electrodes. The patterns and values of the synthetic tomographic models were then compared to LE-ERT field data from the AX tank farm at the Hanford site. This indirect method of assessing the effective resistivity revealed 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 shows reinforced concrete to be generally resistive.

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