The Japanese company in charge of cleaning up one of the world's worst nuclear disasters said Friday its latest error may have caused contaminated water to leak into the ground for nearly half a year. The Tokyo Electric Power Company (Tepco) said it erroneously configured gauges used to measure groundwater levels in six wells near Fukushima No.1 nuclear power plant reactors Nos. 1 through 4, all of which were destroyed when a March 2011 earthquake and tsunami ... caused a series of meltdowns at the plant. The false readings, which have been relied on since April 19 and were discovered this week, meant that groundwater levels were actually more than two feet below what Tepco was measuring. This mistake caused groundwater levels to fall below the limit set to prevent radioactive water from flowing out of the plant and into the nearby wells, known as subdrains, at least once, in May. Between May 17 and May 21, groundwater reportedly fell as much as 7 and a half inches below the safety levels at least eight times. Since the disaster, plant owner Tepco has struggled through the recovery process, the price tag of which was raised to $192 billion last year. The leading obstacle that the company faces is extracting the nuclear fuel that remains in the plant's damaged nuclear reactors. Japan's latest plan to clean up the site did not make any mention of what Tepco would do with about 777,000 tons of water contaminated with tritium, a nuclear byproduct.