FPS drops

First of all, this is the most awesome mod i have ever played, NICE WORK!!!

But i experience som heavy fps drop’s, it happens when i enter a new area, meet enemies or just when there is alot of action going on… it can be as low as 20fps!?

My setup are:
3930K@4.7Ghz
16GB Ram
HD 7970 Crossfire

I only play on one card, but why all this low fps? is it because its a earlier version of the Source engine? any settings/things i can do?

Thanks

Founded in 2004, Leakfree.org became one of the first online communities dedicated to Valve’s Source engine development. It is more famously known for the formation of Black Mesa: Source under the 'Leakfree Modification Team' handle in September 2004.