Recently 1.4 million Bq/liter of all-beta radiation (including strontium-90) was detected in groundwater near Unit 2 of the destroyed Fukushima Daiichi nuclear plant, a new record. Tepco, for some, reason, has not released the actual Sr-90 levels, though.
But Fukushima Diary has an entry stating that Tepco has released Sr-90 levels from groundwater near Unit 1, the sample collected Sept. 11. They found 7,500 Bq/liter of strontium-90, where 9,500 is all-beta. Strontium-90 only emits beta radiation.
It can be inferred that the main component of the increasing record beta levels is the extremely dangerous isotope strontium-90. Last March, Tepco found strontium-89 in groundwater also.
These strontium isotopes collect in bone marrow, and cause bone cancer, leukemia, and immune system damage. You can be sure that this groundwater will be entering the Pacific sooner or later.