Lots of all-beta (that includes strontium), tritium, but not so much cesium or gamma emitters.
But first, let's do the quick recap of the water treatment system at Fukushima I Nuclear Power Plant that has been operational since mid 2011:
Water (filtered water + treated water) is injected into the reactors to cool the corium.
Water gets highly contaminated with radioactive materials from the corium, accumulates in the basements of the reactor buildings and turbine buildings which are connected.
Highly contaminated water get somewhat diluted by the groundwater seeping in (400 tonnes a day).
The water is then transported from the turbine building basements to either Central Radioactive Waste Treatment Facility or High Temperature Incinerator Building, which have been converted to storage of contaminated water.
From these buildings, the water is transported to Cesium Absorption Apparatus (which is currently Toshiba's SARRY only; Kurion's system has been off-line for a long time now, and AREVA's co-precipitation decontamination system is not used anymore). Most of radioactive cesium is removed by this process, from tens of thousands of becquerels per cubic centimeter to ND or close to ND. This water still contains high tritium and high all-beta. It also contains chloride, from the seawater injection in the early days of the accident in 2011.
The water treated at SARRY then undergoes desalination process, using Reverse Osmosis Apparatus to remove chloride. (Evaporative Concentration System, another desalination process, is not currently used.)
After being treated by Reverse Osmosis Apparatus, the water, though still high in tritium and containing all-beta (which cannot be removed at this point, as ALPS has been halted and there is no effective way to remove tritium), is mixed with filtered river water, and gets injected into the reactor.
The waste water after reverse osmosis process, high in chloride and high in all-beta and tritium, is stored in the tanks (assembled metal tanks or welded tanks), and this is the water that is found leaking from the tank(s) this time.
Here's the latest nuclide analysis of water at different stages of water treatment, published on August 8, 2013. No.8 water (in red rectangle) is the RO waste water:
Cs-134: 1.1E+00, or 1.1 Bq/cm3
Cs-137: 2.7E+00, or 2.7 Bq/cm3
Sb-125: 3.0E+01, or 30 Bq/cm3
Tritium: 7.7E+02, or 770 Bq/cm3
All-beta: 7.5E+04, or 75,000 Bq/cm3