Electrical Resistance Tomography Of Unsaturated Flow And Transport In Yucca Mountain

Electrical Resistance Tomography (ERT), a new geophysical imaging technique, was used to study<br>the movement of a tracer through the test block at the Unsaturated Zone Transport Test (UZTT) at<br>Busted Butte, Nevada. Data were collected four times starting in July and ending in early<br>September, 1998. ERT baseline images show a resistivity structure which is consistent with the<br>known lithology in the rear part of the test block. There appears to be a low resistivity region in<br>the front half of the block, particularly near the bottom. Difference images from August 19 and<br>September 9 show clear and consistent resistivity decreases in the region near injection holes 18,<br>20, and 21 which can be associated with the injection of conductive water. The images show very<br>little effect in the region around the other injection holes, 23, and 24 through 27 where far less<br>water was injected. Difference images from August 19 and September 9 show resistivity decreases<br>which could be interpreted as water moving down into the block. This is the same region which<br>has an anomalously low resistivity in the baseline image. These results should be considered<br>preliminary, and are subject to further interpretation.