Garden Abstraction

Husband Dear found this concrete slab in one of the corners of the garden, buried deeply underneath the leaves. After some investigation of the ground surrounding the slab, he suspects a crack in a sewer line. We won't really know until it rains. If there is a crack, the soil on the top will be sucked into the pipe and will look indented. I am terrified to find out how much will fixing the pipe cost us...

Here is the concrete slab, busted up, ready for removal.