The soil column above the water table around the tanks and below them, known as the vadose zone, has been contaminated by these leaks. Other dumping has also contaminated the Hanford vadose zone. The highly contaminated vadose zone poses a severe risk to the most important surface water resource in the northwest, the Columbia River, which runs through the Hanford reservation. A failure to remediate the vadose zone and to empty the tanks of their radioactive waste would present a continuing threat to the region and its people and economy that could have unforeseeable negative consequences. DOE is moving some of waste from single shell tanks into double shell tanks to reduce the risk of leaks.
Recent data show that contamination from leaking tanks appears to be worse than previously thought.
The report gives a lower-bound estimate of about half this amount. The report contains no analysis of the sensitivity of the results to variations in its assumptions about key parameters and notes that there is a great deal of uncertainty, but the new estimates of the volumes of waste that leaked are much higher than earlier ones. The radioactivity estimates are also higher. The previous estimate of the amount of cesium-137 in all the contaminated liquid that has leaked from all tanks was approximately 1 million curies. Table 2 shows various estimates of volumes of liquids that have leaked from these four tanks.