(UPDATE 8/25/2013) The reason for the ad hoc presser is explained in the new post.
The press conference will start at 6PM on August 24, 2013 (Japan Standard Time) at TEPCO's Tokyo Headquarters.
What could that be that makes an ad hoc press conference necessary? (TEPCO's regular press conference is on Monday, Wednesday and Friday at 6PM.)
You can view the press conference live at TEPCO's page:
Meanwhile, Jiji Tsushin (8/23/2013) has a bit of information on what's beneath the concrete platform on which the huge waste water tanks assembled from steel sheets, bolts and nuts, rubber packing and anti-corrosion epoxy paint stand.
According to Jiji,
Tanks sit on the concrete that's 20-centimeter thick.
There is a 1-meter-thick layer of amended soil mixed with cement to make it harder for water to pass through.
Groundwater flows at the depth of 5 to 7 meters from the ground surface.
Jiji's article is about TEPCO's plan to conduct a boring survey around the tanks. I think this is what Nuclear Regulatory Authority strongly suggested TEPCO to do. NRA's Commissioner Fuketa visited the plant on August 23, and he requested TEPCO to inspect ALL tanks including welded tanks.
Given the corrosion and leak from the welded ALPS tanks, welded tanks at the plant may not be so leak-proof.