The T1, T2 and T3 geological layers include tuff [volcanic rock]

The Geology of Fukushima
[link to fukushima.over-blog.fr]

[snip]

Good and bad news

The good news is that the radioactive water leaking from the plant will not be able to spread towards the Japanese inland and the Abukuma plateau due to the downward slope of the geological layers. The bad news is that there exists a fault which appears to be active right under the Fukushima Daiichi plant itself: this allows, and will continue to allow, radioactive pollution of aquifers over a depth of several hundreds of meters, as it runs through the different "waterproof" strata (4). This also means that the radionuclides will naturally be carried towards the sea by this underground water stream flowing through the permeable layers of sandstone. Sandstone is indeed the ideal rock for aquifers, as it is both permeable and fractured, providing easy movement of water. And finally, there is the problem of the type of rock on which the plant was built being rather "soft", meaning that an earthquake can only destabilize the buildings.



As early as March 31, 2011, Tepco announced that the groundwater was contaminated with radioactive iodine, according to an analysis of a sample taken at a depth of 15 meters under the first reactor (link). Today, if one or more coriums have sunk into the ground, this pollution has very likely been increasing. But Tepco no longer shares any information about the pollution of groundwater. Their only concern is to present a beautiful reassuring façade, which will never solve this disastrous pollution of soil and groundwater: underground contamination is irreparable, because there is no access to it.