Groundwater contaminated with highly radioactive substances has been detected from a monitoring well just 27 meters from the seashore within the compound of the crippled Fukushima No. 1 nuclear plant, Tokyo Electric Power Co. said Wednesday.

Wednesday's announcement is the latest in a series of difficulties Tepco has faced as it struggles to manage contaminated water at the wrecked plant, posing a great risk to the environment.

Testing revealed strontium-90 readings of 1,000 becquerels per liter, 33 times more than the legal limit, as well as tritium readings of 500,000 becquerels per liter, 8.3 times the limit.