Repairing water mark on table.

[cacran]

I have bought an old coffee table which needed some work doing to it. The varnish on the top was flaky so I sanded it back to the veneered finish. I think it is MDF underneath. I discovered a risen circle which looks like a watermark. I have snded it as much as I datre, without going through the veneer but it is still risen and showing. I do not want to varnish the top, just to polish it to a nice even finish. Has anyone out there got a method of sorting this?? :?: