Iodine-131 was found repeatedly in 20111, 2012, 2013, 2014 and 2015, proving that something is still fissioning in the Fukushima Daiichi nuclear plant.
According to Gunma prefectural government, 24 Bq/Kg of I-131 was detected from dehydrated sludge of a sewage plant.
From their monthly report published on 8/7/2015, the sample was collected from 7/27 to 7/29/2015. The sewage plant is situated beside Tonegawa River.
33 Bq/Kg of Cs-137 was also detected from the same sample.
I-131 was detected from 2 of 6 samples in June and May as well. The highest reading was 49 Bq/Kg.
From the sample of 6/23 ~ 6/26/2015, Cs-134 was measured to prove the dehydrated sludge is also under the effect of Fukushima accident.
https://www.pref.gunma.jp/05/h6600137.html
https://www.pref.gunma.jp/05/h6600138.html
https://www.pref.gunma.jp/05/h6600139.html
Source: Fukushima Diary
I-131 detected from dehydrated sludge of sewage plant in Gunma
Fukushima 311 Watchdogs 