Structurally maybe, but a contractor that either didn't notice it or noticed it and did nothing isn't acceptable. If you accept this, odds are you'll get third-rate quality for the rest of the job.
If it hasn't been poured, make them fix it before the pour.
- the experts seem to agree it's not a huge issue (depends on the situation though).
The potential issues with having too much cover are obvious. But whether or not they will actually be issues depends on the situation. The extra 10 inches would affect reinforcement in the slab or beam above, but barely. A bigger concern would be with the architect losing floor space... if there's an architect that is... The solution really depends on the project.
A contractor will generally try to chip-out the concrete then finish it smooth. I'm guessing most structural engineers aren't a big fan of this method (fills the member with micro-fractures). There's ways to avoid the associated externalities... it would actually be a good thesis for someone.
One last thing to note is that it might be worth looking at the drawings and making sure the discrepancy didn't arise from the contractor but rather some sort of coordination issue. Probably about half the time we discover that these issues are actually caused by the contract documents being uncoordinated.
