A network of trenches runs between the reactor buildings and the shore. They are flooded with extremely radioactive water that’s been trapped** there since the triple meltdown. Tepco data shows concentrations of cesium up to 4 million times above the government safety limit. Engineers estimate that the trenches hold about 15,000 tons of toxic water but radiation levels are too high for them to get a more precise look at the situation. Some experts point out these trenches are a source of contamination for the Pacific Ocean. Tepco says there’s no evidence of that yet, but it recognizes the need to act quickly.