Optimized Resistivity Arrays
When conducting electrical resistivity, whether as a two-dimensional profile, three-dimensional block, or four-dimensional time lapse study, the arrangement of electrodes and the method of acquisition are important aspects to consider for ensuring the highest quality of data and resolution of the model. The method of acquisition is called an array and many standard electrical resistivity arrays exist that focus on different target geometries. For example, the dipole-dipole electrical resistivity array is commonly used for defining lateral boundaries while the Wenner array is better for layered media. The pole-pole array is the fastest when conducting time lapse resistivity but has the poorest resolution. The standard set of electrical resistivity arrays for two-dimensional profiling and their geometric factors are shown below.
HGI uses optimized resistivity arrays to enhance subsurface resolution for particularly difficult targets, where details are needed for engineering design.
Standard Electrical Resistivity Arrays
With modern instrumentation, there is no reason to be stuck using standard electrical resistivity arrays that perform differently in different situations. Several years ago, researchers developed optimized resistivity arrays that ensure the highest resolution of the subsurface. HGI uses optimized resistivity arrays to enhance subsurface resolution for particularly difficult targets, where details are needed for engineering design. The optimized resistivity arrays combine some aspects from each of the standard arrays, but add more combinations of measurements that are nonstandard. Technical discussions of optimized resistivity arrays can be found on Google Scholar.
HGI’s use of the optimized resistivity array has allowed us to focus attention on some of the most difficult contamination issues in the United States: the radiological waste plumes disposed at the Hanford Site. Below is an example of using different electrical resistivity arrays over a set of waste trenches that received millions of gallons of waste. Different arrays were tested and the optimized resistivity array showed the highest level of detail that discriminated between different commingling plumes and the relative size of the different plumes, and provided possible verification about which trenches received more waste. The standard arrays tested could not provide this level of detail.
Results of comparing standard resistivity arrays to the Optimized Resistivity Array