nhk world's neil asami shows us how tainted the woods are and examines the impact of not cleaning them up. >> reporter: wawauchi is 20 kilometers from the fukushima daiichi nuclear plant. houses in the village are surrounded by forests. in november, researchers from the japan atomic energy agency conducted surveys to find out how far the contamination has spread. now they constantly measure radiation in the roots. they start near the ground. >> translator: it's 1.87 microsieverts per hour here. that's more than one times what's normal. >> reporter: they took readings in ten locations. the radiation in each place was much higher than what they've measured in decontaminated neighborhoods. >> translator: radiation levels tend to be higher in forests, because the trees are contaminated. >> reporter: the researchers think leaves are emitting high levels of radiation. they wanted to identify any other sources, so they test the forest soil. they gathered fallen leaves, and they collected soil at the depths of one, five, and ten centimeters. they brought mobile labs to test the samples emitted