Electromagnetic experiment to map in situ water in heated welded tuff: Preliminary results

The results of an experiment conducted in Tunnel Complex G at the Nevada Test Site to evaluate geotomography as a possible candidate for in situ monitoring of hydrology in the near field of a heater placed in densely welded tuff are given. The experiment is described. The linear character of many tomographic features and their spatial correlation with fractures mapped in boreholes are evidence that drying was most rapid along some fractures. The interpretation of the tomographs is preliminary until they can be processed without the restrictive assumption of straight ray paths for the signals through the highly heterogeneous rock mass