We have a small stream bisecting out property, an area of about 3 metres either side of the bridge has stone walls to shore up the banks and also the bed of the stream in this area has been concreted over. The concret is covered in weed which I would like to clear, do I put it on the conmpost heap or would it be OK to use as a mulch on the veggie plot? The stream starts off as a couple of springs in the woods above us and there are no farmed areas around so the water is pretty pure.