Clean up code for entire website

We are looking for someone to clean up all of my HTML and CSS code site-wide to ensure cross-browser compatibility. I am ideally looking for someone who is experienced in Responsive Web Design as to make sure the site is friendly for all mobile devices. The site has obviously already been built and I have a staging server that you'd be able to work on. We want to make sure the code is W3C compliant and is as efficient as possible. Must be very experienced in CSS as there is a lot of redundant code. The website is [login to view URL] - the site is built on the 960 grid system using a 12 column layout. We do not want the design to change at all - simply keep it exactly the same, just minify the code and make it as efficient as possible. Must be available on Skype throughout the work week - looking for someone based in the US or working the similar hours.