Majia here: There have been many recent reports of major leaks by most, if not all, of Tepco's water tanks used for containing radioactive water.
The reason containment leaks are significant is that the Daiichi site is saturated with water.
Contaminated ground water at the site could contaminate the fresh water aquifer (indeed, it probably already has).
Furthermore, contaminated ground water will pour into the basements of the reactor buildings. Tepco cannot handle the volume of this water and has not been successful in pumping it all out.
The possibility of highly contaminated water entering the buildings and becoming further contaminated seems given at this point.
That means yet greater contamination of the ground water, ocean, and atmosphere (through radioactive steam emissions).
By SHUNSUKE KIMURA(8 April 2013) ‘Defect could affect all radioactive water storage tanks at Fukushima plant’ Asahi Shimbun, http://ajw.asahi.com/article/0311disaster/fukushima/AJ201304080089
[Excerpt] Groundwater has been flowing into the reactor buildings, creating 400 tons of radioactive water daily.
TEPCO planned to pump up groundwater and release it into the sea before it enters the reactor buildings. That plan would be meaningless if the groundwater is already contaminated. [end]