My terrain data is stored in a voxel format and originally I was generating it in cubes and it was simple to remove a block of the terrain (just subtracted half of the normal from the hit of a raycast). My problem is although I have the same data structure, I’m not rendering my chunks with the marching cubes algorithm. Although it looks nice, I am having a lot of difficulty figuring out how to accurately remove the terrain block that the player expects based on the raycast hit method.
The solution is proably hidden somewhere in this thread 
http://forum.unity3d.com/threads/after-playing-minecraft.63149/