Tokyo Electric Power Company says it detected 2,300 becquerels of tritium per liter of seawater collected from a port near the nuclear plant on Wednesday.

That's twice the amount detected about 2 weeks ago, and the highest since monitoring began in June 2011.

But the figure is still about one-twenty-fifth of the government-set limit for water to be released into the sea.

The tritium found in seawater stayed at around 100 becquerels per liter for one year through April. But it started to rise in May.

On Friday, TEPCO workers tested water collected from a well near the port. They detected 900,000 becquerels of radioactive substances, including strontium, per liter.

That's the highest level ever found in samples from observation wells.

TEPCO officials say they have yet to confirm the cause of the spike in readings, but they cannot rule out the possibility that contaminated groundwater seeped into the sea.

The company plans to build more observation wells and solidify the ground to prevent underground water from reaching the ocean.

http://www.tepco.co.jp/en/press/corp-com/release/2013/1228742_5130.html