using two different 'permalink' structures

My core site has been in place for some time and is entirely running on WordPress. My url’s are set to resolve like a traditional site, eg: ‘site.com/page.html’.

We have recently added a ‘Blog’ section and every blog post is, understandably, resolving as ‘site.com/postname’. What I would like to do is have only the blog portion of the site resolve as ‘site.com/blog/postname’ while leaving the core site url structure (about, contact, etc pages) as is; preferably without breaking any backlinks to the existing content but if that part is impossible, so be it.

I assume there is a fairly simple way to accomplish this (perhaps with a mod_rewrite rule in the htaccess?) but I am currently stumped. Any help would be greatly appreciated. This is my first post on the forums and I did attempt a search but was unable to find anything that addressed this issue specifically. My apologies if I missed it.