If concrete acts anything like rock, the movement most fission products or decay products will be greatly slowed down by the concrete, so it would be very possible to have water coming thorough but little radiation. Some elements aren't really affected though, iodine, for example, will move at the same speed as the ground water, not slowed at all. It depends a lot of the porosity of the rock however, and I'm not sure how concrete measures up.

As for gamma rays, since they are simply high energy photons, a lot of concrete can be a pretty effective shield. At least, as long as your sources stay outside the concrete.

As with anything, take this with a grain of salt. I'm not consulting a book for this, I'm simply trying to remember what I can from my waste class. We were looking at the movement of waste from failed packages in a geological repository, but the concept seems pretty similar.