Jiji Tsushin (4/13/2013) says TEPCO has reported to the Nuclear Regulatory Authority that the in-the-ground water storage pond No.1 is indeed leaking into the surrounding soil.
TEPCO's handout for the press on April 13, 2013 shows that beta nuclides are being detected in the water taken from either the drains or the leak detection pipes or both in not only the ponds Nos 1, 2, 3 but all seven of these in-the-ground storage ponds:
(Click to enlarge)
The top table is for the sampled water from the drain holes, which are placed outside the bottom bentonite layer.
From the presentation material by TEPCO's President (4/10/2013), Page 7:
Confusing information about which pond had the highly contaminated waste water after the Reverse Osmosis (RO) treatment. Ponds Nos 1, 2, 3 have them for certain, and Pond No.6, I think. According to the TEPCO president presentation, Pond No.5 (capacity 2,000 tonnes) and Pond No.7 (capacity 4,000 tonnes) were empty.