3-D Ert Inversion Used To Monitor An Infiltration Experiment

The purpose of this project was to test the capability of 3-D electrical resistance<br>tomography (ERT) to monitor changes in vadose zone moisture content movement.<br>The infiltration took place on a 50 m x 50 m plot at the Maricopa Agricultural Center,<br>- located in Maricopa, Arizona. After background data was collected, the field was<br>infiltrated with water of low salt concentration. Data collection was frequent (bi-weekly)<br>during the beginning of infiltration and less frequent (weekly) towards the end of<br>infiltration and for several weeks after infiltration ceased. The ERT experiment consisted<br>of 12 boreholes, spaced 10 m apart, along two east-west lines. In each borehole, 15<br>electrodes were spaced 1 m apart vertically. Data was collected in 3-D blocks consisting<br>of planes of data between different pairs of boreholes. Data sets for each block were<br>inverted to get a 3-D image of resistivities. A variety of other hydrogeological and<br>geophysical methods used at this site provided ground truth for evaluation of the ERT<br>interpretation. The inverted ERT data corresponds closely with neutron probe and EM-39<br>data collected from 6 deep boreholes (-15 m deep) located near some of the ERT<br>boreholes. The 3-D ERT inversion technique was capable of monitoring vadose zone<br>moisture content movement and provided a realistic image of infiltration events.