We developed a novel cokriging approach to convert electrical conductivity derived from<br>three-dimensional (3-D) electrical resistivity tomography (ERT) data and neutron-derived<br>moisture content into a 3-D moisture content distribution. This provided a complete picture about<br>the water movement in an infiltration experiment at the Socorro-Tech vadose zone (STVZ)<br>facility in Socorro, New Mexico.<br>3-D hydrological monitoring is extremely expensive due to the number of boreholes<br>required to accurately image the area. ERT, however, is a fast and inexpensive technique<br>designed to estimate the 3-D moisture content distribution and monitor an advancing wetting<br>front. A vadose zone field site was built to test both hydrological and geophysical techniques for<br>vadose zone monitoring. Thirteen neutron boreholes were installed at the site for direct<br>measurements of moisture content and eight vertical electrode arrays were installed for ERT<br>measurements.<br>Cokriging results indicated that 3-D electrical conductivity data together with neutronderived<br>moisture contents provided an excellent estimate of the 3-D moisture content<br>distribution. The effect of the number of neutron wells used for the cokriging was investigated to<br>determine the optimum results for the least input. We found that a neutron well in the center of<br>ERT mesh where no VEA exists played an indispensable role in cokriging estimates. The center<br>neutron well along with the ERT data provided a fairly good result for limited amount of data<br>used. The results suggests that cokriging of ERT and neutron data is a fast and effective<br>technique for obtaining the 3-D in-situ moisture content distribution and for 3-D monitoring of<br>an advancing wetting front.


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