Sand on Concrete

[Terrie Mac]

This was our first winter with chickens. We have limited space so had to place the chicken run on concrete and layered it with a few inches of sand. It gets wet in there during the winter (Ca.) so then I pile on "muck buster" (wood chips). Today I started removing the chips and turning the sand and gagged from the stinky wet sewage smell coming from down under. It doesn't have any place to soak into. I loved having the sand when it was dry, the flies were few and daily clean up was easy but wondering if I need to rethink what's best for our setup - considering the lack of drainage (except for runoff).

Any suggestions out there?